from the rarities committeeâ€™s files identification of caspian gull

142 © British Birds 103 • March 2010 • 142–183

From the Rarities Committee’s files

Identification of Caspian GullPart 1: typical birdsChris Gibbins, Brian J. Small and John Sweeney

Abstract This paper deals with the identification of the Caspian Gull Laruscachinnans. The aim is to synthesise what is currently known about theidentification of this species and discuss the appearance of proven and suspectedhybrids. The paper is split into two parts. Part 1 deals with the identification oftypical cachinnans and their separation from Herring L. argentatus and Yellow-leggedL. michahellis Gulls. It is targeted at non-specialists who remain unsure of the mostreliable identification criteria, and at local records committees who need astructured basis for assessing claims. The paper covers all age groups, butconcentrates particularly on those treated in less detail in the published literature.It includes a summary table that distils key information and ranks criteriaaccording to their value in field identification. Part 2, to be published in a futureissue, will deal with the identification of less typical individuals and hybrids.

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IntroductionRationale and aimOur perception of the Caspian Gull Laruscachinnans as a British bird has changed dra-matically in the past 20 years. It has gonefrom being a poorly known, southeasternrace of Herring Gull L. argentatus (Grant1986) to being recognised as a valid species(Leibers et al. 2001; Collinson et al. 2008)that regularly occurs in Britain. This trans-formation has been due, in no small part, tothe groundbreaking identification studies ofKlein (1994), Gruber (1995), Garner (1997),Garner & Quinn (1997) and Jonsson (1998).Subsequent contributions (e.g. Bakker et al.2000, Small 2000, Gibbins 2003) built on thispioneering work. Along with that of MallingOlsen & Larsson (2003), these studies havedemystified this gull to the extent that itsidentification may now be considered ratherpassé by some birders. But can we really closethe book on the identification of cachinnans?

An identification review is timely, giventhat BBRC has now passed assessment ofpost-1999 claims to local committees. More-over, there is anecdotal evidence that manyobservers are still struggling with the identifi-cation of Caspian Gull. Understandably, thisis chiefly the case in areas where cachinnansremains truly rare and where observers havehad little chance to gain first-hand experi-ence. The key problems are confusion overthe most reliable identification features and afailure to appreciate fully the normal vari-ability shown by cachinnans and similar taxa.Some identification problems merely reflectthe extremes of variation shown by cachin-nans; others stem from hybrids, originatingfrom the mixed-species colonies in centralEurope (Neubauer et al. 2009); and someproblems may occur with birds that have nocachinnans genes but which represent theextremes of variation in other species. Wehave arrived at a point where we should takestock of what we know of the identificationof typical cachinnans and begin to look moreclosely at the identification of less typicalindividuals and their separation fromhybrids. Are there clear dividing lines, and ifso where are they?

The aim of this paper is to provide a dis-tillation of known criteria, assess their meritsand, for the first time, discuss the identifica-

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Identification of Caspian Gull

tion of less typical and hybrid individuals.We hope that it will be of value to bothbirders and local records committees. Part 1deals with typical individuals. We describe indetail the plumage and structure of typicalbirds, emphasising key average differencesfrom Herring Gull and Yellow-legged Gull L.michahellis; we outline normal variation butleave the extremes aside. Appendix 1 sum-marises key distinctions between typicalcachinnans, michahellis and Herring Gull andranks criteria according to their relativeimportance. It should not be used in isola-tion, but as a convenient summary and as anentry point to the details in the text. Lesstypical and extreme individuals will be dealtwith in part 2, where we shall also discuss theidentification of hybrids; this will be pub-lished in a future issue.

To date, literature on cachinnans hastended to focus on one or two age groups –the first-winter and adult birds that arefound most regularly in Britain. To redressthis balance, we pay particular attention toother age groups. The paper is intended pri-marily for birders in Britain, so does notdiscuss Heuglin’s Gull L. fuscus heuglini. Thistaxon can look remarkably cachinnans-like instructure and some immature plumages.However, serious confusion is unlikely:heuglini has a different call, dark inner first-generation primaries, and once adult-typegrey feathers develop their tone is muchdarker than those of cachinnans.

Circularity and the empirical basisof this paperCircular reasoning (bird A is a Caspian Gull,it shows features X, Y and Z, therefore X, Yand Z are features of Caspian Gull) mayundermine attempts to develop identificationcriteria. Circularity can be avoided if: (a) thespecies is studied in the core of its acceptedbreeding range, where potential confusionspecies are absent and hybridisation is not asignificant issue; or (b) the sample consistsonly of individuals of known provenance(ringed birds). Much of our knowledge ofcachinnans is actually based on unringedbirds observed in western Europe in winter,well away from core breeding areas and onthe edge of the wintering range. Circularity isthus a potential problem, especially because

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of the risk of incorporating an unknownnumber of hybrids into the ‘cachinnans’sample. Moreover, as we may be picking uponly the most striking birds in Europe, thereis a danger of developing criteria based on anunrepresentative sample. Studies of cachin-nans wintering in the Middle East suffersimilar problems, owing to the presence ofextremely similar taxa whose identificationhas yet to be fully resolved (notablybarabensis). Access to the heart of thebreeding range of cachinnans, where bothHerring and Yellow-legged Gulls are absent,is difficult and few western ornithologistshave studied the species there. Consequently,we are largely constrained to studying cachin-nans in wintering areas and must be aware ofthe problem of circular reasoning.

Circularity is most problematic with lesstypical individuals. In part 2 we therefore useringed individuals of known provenance tohelp to develop criteria for the separation ofhybrid from pure individuals. Circularity isless of an issue with the ‘classic’ birds that arethe focus of part 1. Nonetheless, to studycachinnans we have travelled to parts of thebreeding range (e.g. several trips to theDanube Delta, Romania) and areas of thesouthern Baltic where cachinnans occurs inlarge numbers in the immediate post-breeding period and can be the most abun-

dant large gull at some localities (e.g. on theCuronian Spit in Lithuania). The majority ofplates show birds from these areas. Since thepaper is aimed at British birders, it may seemthat examples of cachinnans photographed inBritain are under-represented in the plates;this is a product of the need to limit theproblems of circularity.

‘Herring Gull’ is used here to refer collec-tively to both races; ‘argentatus’ is used whenreferring specifically to the Scandinavian/Baltic race and ‘argenteus’ when referring tothe British/west European race. Yellow-leggedGull is referred to as ‘michahellis’ and relatesonly to Mediterranean birds. The AtlanticIsland populations of Yellow-legged Gull rep-resent a taxon whose status is still debatableand which, in any case, have rather darkimmature plumages and structural traits thatmake them unlikely to be confused withcachinnans. We treat cachinnans as mono-typic, as the extent and nature of geographicplumage variation has yet to be firmly estab-lished. Nonetheless, future work may revealconsistent differences between eastern andwestern birds (see section on adults). Fig. 1illustrates key terms used in the text.

Patterns of occurrence in BritainIt is difficult to assess the number of cachin-nans currently occurring in Britain each year.

This relates chieflyto the fact that thespecies is now soabundant in someareas that observersdo not necessarilyreport all sightings.Nonetheless, it isclear that cachin-nans is recordedmore frequentlynow than in the pastand that there arestrong seasonal andgeographic patternsto its occurrence.Caspian Gulls aremost frequent insouthern England,particularly thesoutheast. The firstbirds arrive in late

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48. A lone Caspian Gull rests with a group of Herring Gulls on a landfill sitein Poland (17 Jan 2004). Can you see it? It is white-headed, dark-eyed and isholding its bill distinctly downwards. Some fine ‘pencil’ streaks are visible onthe lower rear neck. It is below-right of centre.

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summer and early autumn, when themajority of records come from the coastlinebetween Kent and Suffolk. Juvenile cachin-nans now occur regularly in early August,when many young British Herring Gulls arenot even fully independent. These cachinnansare not necessarily from the nearest breedingareas, since juveniles may disperse far fromtheir natal colony soon after reaching inde-pendence. For example, a bird at Espoo,Finland, on 26th July 2004 had been ringedas a pullus on 27th May on the River Dnperin southern Ukraine (49°46’N 31°28’E). Con-sequently, observers should be looking outfor first-calendar-year (1CY) cachinnansfrom late July onwards. Post-breeding adultstend not to be seen in Britain until later inthe autumn; this delayed arrival may belinked to the progression of primary moult.

Following their arrival, many birds moveinland and disperse northwards as theautumn and winter progress. They are sup-plemented by new arrivals, perhaps linked tocold weather on the Continent. For example,hundreds of cachinnans are present atlagoons along the coast of Lithuania in

autumn but these disappear in midwinter,once the water freezes (Vytautas Pareigispers. comm.). The largest numbers of cachin-nans in Britain are recorded in winter, withbirds seen regularly on favoured landfill sitesand in reservoir roosts in southern andcentral England. However, they remain dis-tinctly scarce in north and northwest Britain;there are few records north of the River Teesand the species remains extremely rare inScotland (fewer than five records) andIreland. Very few are recorded in the summermonths. This probably reflects the movementof birds back to the Continent, but perhapsalso the relative difficulty of identifyingmoulting immatures in summer and the factthat gull-watching in Britain tends to be awinter pursuit.

IdentificationSize and structureCaspian Gulls can be strikingly large, tallbirds, but most individuals are similar inlength and weight to Herring Gull and so donot stand out on size alone. However, cachin-nans is structurally distinctive at all ages,



Fig. 1. Key terms, feather groups and plumage features referred to in the text. All images showcachinnans: upper two are from an adult (Latvia, April 2009), lower left is a 1CY (Romania, September2006), lower right is an adult (Romania, September 2008). All images Chris Gibbins.

long white tip to P10

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often described as ‘lanky’ or ‘gangly’. It hasrelatively long, thin-looking legs (the extralength is particularly noticeable in the tibia)and often seems to stand taller than HerringGull. Next to michahellis, its legs tend to looklonger and less robust. However, somemichahellis are long-legged compared withHerring Gulls, so observers should bemindful of this when confronted with anapparently lanky bird. There are marked dif-ferences in size and structure between maleand female cachinnans (see Malling Olsen &Larsson 2003) and these differences may bemore marked than for other large gulls(Gibbins 2003). Some, presumably males, canlook incredibly long-legged, yet others, pre-sumably females, can actually look rathershort-legged. Consequently, birders and com-mittees should not automatically dismiss abird that lacks the textbook long-legged look.

The head can appear oddly small for thebody, generally looks pear-shaped, and nor-mally lacks the bulky feel of the head ofHerring Gull and (especially) michahellis.The head often looks ‘anorexic’, as thoughthere is little flesh covering the skull; thismeans that head shape equates more closelyto skull shape than for other large gulls. Theoften-quoted, but perhaps over-emphasised,‘snouty’ look is due to a combination of thelong sloping forehead and the relatively long,slim bill, which gives the front of the head atapering, ‘pulled-out’ appearance. Thissnouty look can be a striking and definingfeature, but it is important to note that notall cachinnans show it. For a significant pro-portion of (presumed) females, the billlength is unremarkable, and, because of theirhigher, more rounded heads, they may recallCommon Gull L. canus. Conversely, somelarger males can have a robust bill and asolid, more angular head that overlaps inappearance with both Herring and Yellow-legged Gulls. Yellow-legged Gulls typicallyhave a deeper, blunter bill and a larger, moreangular head, yet, as with other gulls, malesand females can be rather different, and theslighter individuals overlap with Herring andeven Lesser Black-backed Gulls L. fuscus. Fur-thermore, michahellis from the Atlantic coastof the Iberian Peninsula tend to be smaller,less robust and less rangy than Mediter-ranean birds.

Most Caspian Gulls appear longer-billedthan Herring Gull and michahellis. They havea more gentle, even curve to the culmen anda less obvious gonydeal angle; unlike HerringGull and michahellis there is little or nobulging at the gonys and the general impres-sion is of a gently tapering bill. Data inMalling Olsen & Larsson (2003) indicate thatthere is actually much overlap in the billlength of cachinnans and Herring Gull(males: Herring 46.4–64.9 mm, mean 54.6,cachinnans 50.7–63.5 mm, mean 56.3;females: Herring 44.9–59.0 mm, mean 49.7,cachinnans 48.0–59.5 mm, mean 51.9). Thus,the longer-billed impression given by cachin-nans results from the interaction of its shape,depth and length, accentuated in some birdsby the pear-shaped head and long neck.

Gibbins (2003) assessed the ratio betweenbill length and gonys depth (measured fromphotographs; length and depth as indicatedin fig. 1) in a sample of Herring and CaspianGulls (n = 68). Most Herring Gulls werescored as having a ratio of 1.75–2.00 whereasmost cachinnans were scored as 2.25–2.50.Thus for cachinnans the bill is most oftenmore than twice as long as its maximumdepth, while for Herring it is most frequentlya little less than twice its maximum depth.Some cachinnans can be extremely long- andslim-billed, with ratios up to 3.25, comparedwith a maximum of 2.5 in Herring. Note thatbill deformity is not uncommon among gulls(especially first-years), so a long, slim bill isnot, in itself, sufficient for identification orrecord acceptance.

The body shape of cachinnans is subtlydistinctive. One of the most noticeable fea-tures is the attenuated rear end; this is a con-sequence of a flat back, limited or absenttertial step and relatively long wings. The tipof the tail falls one-third to halfway along theexposed primaries, while on Herring Gull itusually reaches halfway or slightly further(this comparison holds good only for birdsthat are not moulting their outer primaries).Herring Gulls and michahellis are generallyless attenuated and have a more prominenttertial step although, especially in hotweather, michahellis can appear to have a verylong rear end. The belly profile of cachinnansoften continues behind the legs as a ventralbulge that sags below the wings, making the

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underbody resemble a boat keel in shape.This may be obvious for some birds yet notapparent for others. At rest, compared withHerring Gull and most michahellis, cachin-nans has a higher chest, with a slightly‘bosomed’ effect, as if holding its breath. Thisstance is exaggerated by the long wings andventral bulge, which, along with the head andbill shape, give the most typical birds aninstantly recognisable jizz.

In flight, the long- and broad-wingedappearance of cachinnans may catch the eyeof regular gull-watchers. Compared withHerring Gull and michahellis, the greaterlength of the head, bill and neck extension infront of the wings is also noticeable.

To summarise, the most typical cachin-nans have a striking jizz, much more eye-catching than that of michahellis. They can bea large yet elegant gull, easily located inmixed flocks. However, some lack therangy/gangly/snouty character usually associ-ated with the species and so are much lessdistinctive. Weather conditions and postureinfluence appearance, and in hot conditions,when their feathers are sleeked down, cachin-nans may look very slim, long-legged andlanky. On coldwinter days theylook quite dif-ferent, and experi-ence from birdingholidays in theMiddle East maynot translate wellto Britain.

Behaviour andvoiceCaspian Gulls mixfreely with otherlarge gulls in bothfeeding and restingareas (plate 48).When feeding onrubbish dumps,large individualsare often extremelyaggressive (more sothan Herring andmichahellis) anddominate favouredpatches. Caspian

Gulls habitually raise their wings, especiallyin aggressive encounters, and this can be aneasy way to locate them in groups of feedinggulls.

Their calls (appendix 1) also attract atten-tion and can be heard clearly even above thenoise created by large numbers of squabblingHerring Gulls. The importance of the longcall and long-call posture in separatingcachinnans from other large gulls has beenrather underplayed in the literature and it isclear that not all birders are aware of theirvalue. Calls are always difficult to capture inwords and the long call of cachinnans hasbeen described in various ways. The full longcall is a loud, rapid ‘haaa-haaa-haa-ha-ha-ha-ha-ha-ha-ha’, with a characteristic nasal,laughing quality, very different from HerringGull’s. Once heard it is easily recognised.Adults frequently give shorter versions of thiscall (the last six or seven notes) duringaggressive encounters. Evidence suggests thatthe full long call takes time to develop: inAugust and September, 1CY birds give amuch more subdued version (Hannu Kosk-inen, pers. comm., CG pers. obs.). Juvenilesoften also give screeching calls, especially



49. Adult Caspian Gull, Latvia, 11 Apr 2009.This large male was typicallyaggressive and, as pictured here, incessantly gave the rapid, laughing call whichis diagnostic of Caspian Gull. Unlike Yellow-legged and Herring, Caspian Gullshold their wings open when giving the long call – the so-called ‘albatrossposture’.The characteristic primary pattern is visible here: note the greytongues eating into the black wing-tip on the upperside of P7–10 and the long silvery tongue on the underside of P10. Like Yellow-legged Gull, Caspianusually has a broad, black subterminal band extending unbroken across P5,but there is much individual variation and this bird has only isolated blackmarks on the outer and inner webs.

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when coming in to land to join a feedingmelee. These calls are very high-pitched (theyhave a clear squealing quality) and, onceheard, are distinct from the whine of juvenileHerring Gulls.

The full long call is frequently accompa-nied by the ‘albatross posture’, with wingsopen and held back and the head raised pro-gressively as the notes are delivered (plate49). Herring Gulls and michahellis keep theirwings closed when long-calling, so this is akey distinction. Herring Gulls raise theirheads only to approximately 45° when long-calling, while both cachinnans and micha-hellis often (but not always) raise them to90°.

Juveniles (1CY birds in July–September)Moult and wearThis section deals with a period when bothfully juvenile birds and individuals moultinginto first-winter plumage may be encoun-tered. Plates 50–58 show a selection of birdsphotographed during this period; captionsemphasise key identification features.

Caspian Gulls in fully juvenile plumagemay be seen in July and early August, but bymid August many have commenced theirpost-juvenile moult (the partial moult intofirst-winter plumage). By early September itis rare to find a cachinnans with a full set offirst-generation feathers – most have at leastsome new scapulars and some have a few newcoverts and tertials.

Both cachinnans and michahellis hatchmuch earlier in the year than Herring Gullsand this contributes to their earlier post-juvenile moult. The stage of scapular moultseen in early to mid September among 1CYcachinnans is not reached until late Octoberin many British Herring Gulls. The differencebetween cachinnans and northern argentatusis even greater, with many of the latterretaining some or all of their first-generationscapulars throughout the winter. The extentof wear and fading differs among the species,but is likely to be a function of environmentalconditions in breeding areas as well as hatchtiming. As with michahellis, it is not unusualto see cachinnans in early September withclear signs of wear on their first-generationfeathers; at this time, young Herring Gulls are

still in pristine condition. Moult timing andwear can thus be very useful in the identifica-tion of 1CY cachinnans (and michahellis) in aBritish context; before mid September, any1CY large gull whose scapulars are mainlysecond-generation is well worth a closer look.In addition, it is extremely rare for HerringGulls to include coverts or tertials in thepost-juvenile moult (<1% of individuals; CGunpublished data from North-east Scotland).Consequently, any 1CY bird in westernEurope with second-generation coverts ortertials and clear signs of wear on remainingfirst-generation feathers may well prove to becachinnans or michahellis.

PlumageFully juvenile cachinnans (i.e. those with onlyfirst-generation feathers) are often quite dif-ferent from the 1CY birds seen in westernEurope in winter; although on averagecleaner-looking than Herring Gulls, they arenot as strikingly white as 1CYs in midwinter.Relative to Herring Gull, textbook juvenilecachinnans have fewer streaks and blotcheson the head and body, and their upperpartshave a rather washed-out, ‘watercolour’ look.The first-generation scapulars and wing-coverts are typically light grey-brown (‘wetmud’) in colour, with narrow, simple, palefringes which tend to lack the large palenotches and indentations found on HerringGull and many michahellis. Rusty tones aresometimes present on the lower rear neck,but otherwise the overall colour is a rathergreyish ‘mouse brown’, lacking sharp con-trasts. The generally soft tones and featurelesspattern can sometimes be more reminiscentof juvenile Common Gull than Herring Gull.Juvenile michahellis are distinctly darker,more chocolatey brown and often have adark eye-patch that contrasts with an other-wise white head.

The most striking cachinnans have greatercoverts that completely lack pale notches;instead, each feather has a dark basal sectionand a diffuse pale tip that, at a distance,forms a striking pale wing-bar shaped ratherlike the Nike ‘swoosh’. The exact pattern onthe greater coverts varies subtly among indi-viduals (e.g. plates 50–52), but the mosttypical birds have only weak, diffuse andirregular notches on the inner greater

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50. 1CY (juv moulting to1W) Caspian Gull, Latvia,15 Aug 2008. A typical,elegant individual. Apartfrom three or four newupper scapulars, this bird isin full juvenile plumage.

51. 1CY (juv moulting to 1W) Caspian Gull,Romania, 17 Sep 2008.Another typical individual.Note the simple narrowfringes to almost allfeathers, lacking strongnotches; compare thegreater-covert and tertialpatterns with those of theHerring Gull in plate 53.The jizz is distinctive: it is alarge but elegant bird, witha small, pear-shaped head,long tibia and a relativelyslender bill which lacksstrong contours. Note theventral bulge, also apparenton the birds in plates 50 &52.

52. 1CY (juv moulting to1W) Caspian Gull, Latvia,12 Sep 2009.This bird hasmore second-generationscapulars than the previousindividuals.The diffuse paledistal portion of the inner6–7 greater covertscontrasts with their darkbases and forms a wing-bar.On this individual there isalso a hint of a pale baracross the lower mediancoverts.

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53. 1CY (juv) Herring Gull,14 Aug 2008.Typical juvHerring Gulls such as thisshould pose noidentification problems.Note the stocky, compactshape and heavily notchedoverall appearance, with thenotches especially obviouson the greater coverts.Thetertials and scapulars havepale fringes that have clearindentations.

54. 1CY (juv) Yellow-leggedGull, Spain, 13 Aug 2009.A typical, strongly markedmichahellis.The tertials havesimple, sharply definednarrow fringes that extendonly around the distal partof the feather, and thegreater coverts haveextremely obvious notches.There is a dark maskaround the eye.

55. 1CY (juv) Caspian Gull,Romania, 2 Sep 2006. Astriking bird, with a well-marked tail patternand an extensively whiteunderwing.The ‘window’ inthe inner primaries is palerand more distinct than onmichahellis but less strikingthan on most HerringGulls. Note the pale‘lozenges’ on the outerwebs of P2 and P3: theseare less frequently presenton the inner primaries ofmichahellis and, when theyare, are typically smallerand less prominent than on this cachinnans.

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56. 1CY (juv moulting to 1W) Caspian Gull,Romania, 14 Sept 2008.Thisis an example of a bird withdarker inner primaries(overlapping withmichahellis); note also that ithas fine but extensive palebrown barring on theunderwing-coverts.This is the same individual asshown in plate 51.

57. 1CY (juv) Herring Gull,North-east Scotland, 2 Nov2008.A typical individualshowing an extensive paleinner-primary window andheavily marked rump,uppertail-coverts and tailbase. Despite the late date,this bird appears not yet tohave any second-generationfeathers (hence, juvenileplumage).The innerprimaries have a complexpattern of dark arrowheadsand crossbars on a paleground colour.

58. 1CY (juv moulting to1W) Yellow-legged Gull,Romania, 14 Sep 2008. Theunderwing is much darkerthan on cachinnans, with abold pattern of alternatedark and pale bands.Theinner webs to the innerprimaries of this individualare at the paler end of thescale, but note that it lackspale lozenges on the outerwebs of the innerprimaries.

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coverts, much less obvious than those ofHerring Gull and michahellis. Normally, thepattern on the inner greater coverts appearsto be more vermiculation than notching. Abird with strongly notched greater covertsshould be checked carefully for other anom-alous features. Caution is needed with micha-hellis, as some lack notches on their greatercoverts (instead, some simply have sharp palefringes). An oft-quoted feature of cachinnansduring their first winter (1CY/2CY birds) isthe presence of a second pale wing-bar, onthe lowest row of median coverts. This,however, is rarely evident on fresh juvenilesin July and August.

The first-generation tertials of cachinnanstypically have a muddy-brown base and adiffuse pale fringe around the distal portionof the feather. The pale fringe sometimescoalesces with pale oval patches in the centralpart of the feather to form an extensive paletip, reminiscent of the pattern on a juvenileCommon Gull (e.g. plate 50). The exactpattern varies subtly but the key point is thatthe pale fringe lacks the notches of HerringGull (plate 53) and is generally broader andless sharply defined than shown by typicalmichahellis (plate 54).

Most juvenile cachinnans are as striking inflight as they are on the ground (plates 55 &56). From above and below, the generalimpression is clearly different from HerringGull (plate 57), and while they look similar tomichahellis from above, their underside isquite different. The relatively white under-wing is perhaps the most obvious in-flightfeature of cachinnans. This is created by theoff-white ground colour to the underwing-coverts; the secondaries and primaries arealso paler (silvery to off-white) than those ofHerring and michahellis. Most cachinnanshave a degree of soft, grey-brown barring onthe axillaries and underwing-coverts, so theunderwing is not wholly white (e.g. plate 56).The underwing-coverts of Herring Gull aremuch more extensively and strongly markedwith brown and the general impression istherefore of a much darker and ratheruniform underwing. In michahellis (plate 58)the underwing-coverts are heavily markedwith dark, chocolate brown over a pale basecolour, often creating a contrasting pattern oflight and dark bands. However, some micha-

hellis lack such extensive dark marks so froma distance their underwings can look surpris-ingly pale. The incidence of pale underwingsmay be more prevalent in eastern popula-tions of michahellis.

The underwing of some cachinnans isstrikingly white, and photographs suggestthat some birds drop some underwing-coverts and axillaries during their firstwinter; this exposes the paler bases toremaining feathers and heightens the appear-ance of a white underwing. Conversely,observations on breeding lakes in Romania(i.e. birds with known provenance) indicatethat some 1CY cachinnans can have quitewell-marked underwings, with dark brownbarring and spotting across many feathers,especially the lesser underwing-coverts andaxillaries. Such dark birds tend to have morecontrasting underwings than Herring Gulls,as the brown barring sits on an otherwiserather pale ground colour. This creates adegree of overlap with michahellis.

The contrasting black-and-white patternof the rump and tail of cachinnans is strikingin flight and often likened to that of a Rough-legged Buzzard Buteo lagopus. The generalpattern is more like that of michahellis thanHerring Gull. Juvenile Herring Gulls show avariable but usually extensive scatter of darkbars and spots on the rump, uppertail-coverts and tail base. This reduces the con-trast between these areas and the broader,more diffuse tail band, which averages a littlebrowner than that of cachinnans and micha-hellis. Both cachinnans and michahellis have avery dark (black-looking) tail band that con-trasts strongly with the white rump and tailbase. Malling Olsen & Larsson (2003) statedthat the tail band of cachinnans is ‘fuller andmore even’ than that of michahellis. Cer-tainly, the tail band of many michahellis isuneven, being noticeably deeper on thecentral tail feathers. In general, the tail bandof cachinnans is more even in width but onsome it is clearly deepest in the middle, andhence uneven. While many cachinnans thetail band is deep across its whole width, onsome it is no fuller than for michahellis. Inshort, the depth and evenness of the dark tailband are thus of no real value for the separa-tion of cachinnans and michahellis. There is agreater tendency for the dark tail band of




cachinnans to break into a series of narrow,regular bars along its basal edge (e.g. plate55) while the white tips to the tail feathers aredeeper in michahellis than cachinnans,forming a more striking terminal band(Jonsson 1998).

The pale ‘window’ on the inner 4–5 pri-maries is generally less prominent in cachin-nans than Herring Gull. The (ranked) orderof window prominence runs from Herring tocachinnans to michahellis to Lesser Black-backed Gull (virtually no window). InHerring Gull, the inner primaries (both innerand outer webs) are much paler brown thanthe outer primaries, creating an obviouspanel; in michahellis, the outer webs of all theprimaries are much more similar in tone andonly the inner webs of the inner primariesare slightly paler, giving a much less obviouswindow. In cachinnans the pattern is rathervariable but overall intermediate betweenHerring and michahellis: on many, the innerwebs of the inner primaries are distinctlypaler than the outer webs, while the outerwebs of these feathers are almost as dark asthe outer primaries. This produces a morecontrasting, ‘Venetian-blind’ pattern thanseen on Herring Gull and michahellis.However, darker cachinnans are very similarto michahellis, with only slightly paler innerwebs to the inner primaries. Occasionally, theouter webs of the inner primaries of cachin-nans are also paler than the outer wing, sorather than a Venetian-blind pattern theimpression is of a subtle, pale panel.

There are also some differences among thespecies in the markings at the tip of the inner4–5 primaries. Herring Gulls normally have acomplex pattern: individual feathers have amixture of subtle, diffuse pale areas on bothwebs, a dark shaft streak and arrowhead,often with a crossbar (plate 57). The precisepattern varies individually, but the key pointis the complexity. There is no such complexpatterning to the inner primaries of micha-hellis, which simply have a uniform darkouter and a fractionally paler inner web(plate 58). Occasionally, michahellis have asmall and subtly paler oval patch on theouter and/or inner web of some of theirinner primaries (P2–P4/5). Contrary to someliterature (e.g. Garner & Quinn 1997),cachinnans frequently also show such pale

patches. In fact, a large proportion have clear,sharply defined lozenge- or cigar-shapedpatches on the outer web of the inner pri-maries (e.g. plate 55) which are more strikingthan those of michahellis. These are oftenaccompanied by a more diffuse oval patch onthe inner web. When present, these pale areastend to break up the Venetian-blind pattern.However, darker cachinnans lack pale patchesin their inner primaries and so resembletypical michahellis. In general, it seems thatboth cachinnans and michahellis have theouter web of P1 entirely dark, with palepatches present on only P2–P4/5, whereasHerring Gull has pale areas as well on P1.

Overall, the pattern on the inner primariesis useful for separating Herring Gull frommichahellis. Typically, cachinnans sits some-where between the two, but extremes overlapwith darker Herring Gulls and lighter micha-hellis, so the pattern of the inner primaries isonly a supportive feature. Assessment of theprimary pattern requires good-quality flightphotographs.

Bare partsThe bill of 1CY cachinnans usually appearslargely black, with a pinkish base to the lower(and sometimes the upper) mandible visibleat close range. In extreme cases, the bill ofcachinnans (and michahellis) can be exten-sively pale in mid September. This seems tobe a more common feature in these speciesthan in Herring Gull. The legs of 1CY cachin-nans are a pale, washed-out flesh colour,sometimes appearing greyish or bluish flesh.The iris is dark brown.

Birds in their first winter(1CY/2CY birds in October–April)At this age, cachinnans are arguably at theirmost striking and easy to identify (plates 59& 60). The general impression is of a birdwith an extremely white head and body, paleand rather delicately marked scapulars, andwing-coverts and tertials that, especially at adistance, look as though they have beenpainted softly in watercolours.

By October, cachinnans has second-gener-ation mantle feathers, scapulars and, in somebirds, coverts and tertials, representing theprogression from juvenile to first-winterplumage. Second-generation scapulars may


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59. 1CY (1W) CaspianGull, Finland, 20 Oct 2008.This is a rather typical,striking 1W cachinnans.Note that, for example,the second-generationscapulars have a silverytone and only a narrowdark subterminal band andshaft streak.This bird hasnot (at least by this date)included any coverts ortertials in its post-juvenilemoult.

60. 2CY (1W) CaspianGull, Latvia, 9 Apr 2009.Thisbird has the typical pale andsilvery overall appearanceof late 1W cachinnans. Itssecond-generationscapulars lack stronganchors. It has gained manynew wing-coverts duringpost-juv moult and by earlyspring these are faded andblend in with remainingfirst-generation ones.The lower tertials are first-generation, but the upperones are greyer, second-generation ones, probablymoulted during the post-juvmoult.This combination ofmoult and plumage patternis typical of 1W Caspianbut not of Herring Gull.

61. 2CY (1W) Yellow-legged Gull, Spain, 16 Apr2006. The post-juv moult ofmichahellis is similar to thatof cachinnans, but typicallythe second-generationfeathers (visible here in thescapulars, tertials andcoverts) are stronglymarked with bars andanchors.Yellow-legged Gullincludes 0–100% of itscoverts in the post-juvmoult; this bird has had amore extensive moult thanmany and only a few first-generation feathers arevisible in the wing. HerringGulls do not look like thisuntil mid July of theirsecond calendar-year.

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62. 2CY (1W) HerringGull, Latvia, 13 Apr 2009.Note the strongly markedscapulars and heavilynotched greater coverts,as well as the compact jizz.

63. 2CY (1W) CaspianGull, UAE, 7 Feb 2009.Some Caspian Gulls, likethis one, have rather heavilymarked second-generationscapulars and overlap withHerring Gulls in thisrespect. However, note thesecond-generation lesserand median coverts dottedwithin the first-generationones, and the characteristicjizz.

64. 2CY (1W) CaspianGull, UAE, March 2007.By early spring, some 1WCaspian Gulls areextremely pale andabraded, especially thosethat have wintered inhotter climates.The onceblackish areas are fadedbrown and the sun-bleached wing-coverts lackany clear pattern.Theunderwing is gleamingwhite.

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be highly distinctive, typically showing asilvery-grey ground colour (paler grey thanthose of adults) with a simple dark shaftstreak and either a rather diffuse subterminalanchor pattern or a dark basal diamond;most lack strong crossbarring. The silveryground colour fades rapidly as the winterprogresses and the dark markings becomemore subdued, leading to an increasinglypale and uniform-looking bird. On manycachinnans, the lowest row of second-genera-tion scapulars appear paler and more lightlymarked than the rest, and hence form a paleband separating the upper scapulars from thebrown wing-coverts. Younger feathers in amoult sequence may differ in pattern fromolder ones (Howell 2001), which may explainthe presence of this pale band.

Typically, michahellis are quite different(plate 61): their second-generation scapularsare strongly marked with heavy crossbars anda broad, dark anchor near the tip. The samerelative differences occur on any new wing-coverts or tertials moulted in during theautumn: cachinnans usually have simple andsubtle patterns, michahellis strong and boldones. The pattern on the second-generationscapulars of Herring Gull is extremely vari-able (plate 62) but in broad terms is interme-diate between that of cachinnans andmichahellis. The ground colour of eachfeather ranges from pale, sandy brown to midbrown, and most have darker crossbars andan anchor pattern towards the tip. It isextremely rare (perhaps unknown) for genet-ically pure Herring Gulls to have the silvertone and simple dark shaft streak of classiccachinnans. Importantly, however, a signifi-cant proportion of cachinnans have ratherheavily marked second-generation scapulars(e.g. plate 63).

The striking appearance of many cachin-nans during their first winter stems from acombination of the patterns on new second-generation feathers and wear on remainingfirst-generation ones. Wear is especiallyevident on birds reared earlier in moresoutherly and easterly areas, where sunbleaching and sand blasting (on dry beaches)take their toll on feather condition. Even inSeptember, 1CY cachinnans around the BlackSea can be rather worn and shabby. Light‘pencil’ streaking on the head and body pro-

gressively wears away, and can give rise to astartlingly white appearance, compared withHerring Gull. By midwinter, any remainingstreaks are confined to a neat necklacearound the lower rear neck. The white headisolates and emphasises the dark eye. Weartends to simplify and thus emphasise thepattern on remaining first-generation greatercoverts (dark base, pale distal bar) and, onsome, the second pale bar (on the lowest rowof median coverts) becomes prominent. Thefact that this second bar is less frequentlyapparent on the same feathers in late summersuggests that its prominence is related towear and fading.

By spring, most cachinnans look a littlepaler than in autumn, with a more subduedcontrast between the whites, greys, brownsand blacks. The first-generation feathers canlook rather washed-out, with the feather pat-terning less clear. For those individuals thatincluded some coverts or tertials in the post-juvenile moult, these (now somewhat worn)feathers show up as discontinuities on anotherwise juvenile wing (plate 60). On some,pure grey feathers are distributed randomlyacross the scapulars (these may be third-gen-eration feathers grown during the winter),giving an overall impression quite unlikeHerring Gull; in fact, such advanced cachin-nans (and especially those which also havesome second-generation coverts and tertials)are more likely to be mistaken for a second-winter Herring Gull than a first-winter. Theplumage of michahellis also fades over thewinter and those that have retained theirfirst-generation coverts and tertials can be atrap for the unwary. Despite their originalnotched patterns, the worn coverts of micha-hellis can become surprisingly uniform byspring. Similarly, tertial wear makes thefeather pattern more difficult to discern andso it is effectively inseparable from that ofcachinnans. The rangy appearance of somemichahellis means that observers faced with aworn, putative cachinnans in the latewinter/early spring period should be wary.Careful assessments of bill shape, head pro-portions, call and details of the underwingare critical at this time.

During their first autumn and winter, asmall proportion of michahellis moult theirtail feathers (certainly less than 20%, and

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perhaps less than 10%; Hannu Koskinen andVisa Rauste pers. comm., based on studies inItaly and Greece respectively). Herring Gulls(many thousands observed) and cachinnansin northwest Europe (c. 100 first-wintersobserved) normally do not, unless rectricesare lost or damaged. Thus, a late winter/earlyspring 2CY is unlikely to be cachinnans if ithas new tail feathers – it will most likely bemichahellis. However, the wintering range ofcachinnans is large and, for example, thosewintering in the Persian Gulf may follow adifferent strategy; insufficient data are avail-able to assess this.

As the remiges and rectrices are not (nor-mally) included in the post-juvenile moult ofcachinnans, the wing and tail patterns offirst-winters are the same as described abovefor juveniles. However, by late winter cachin-nans tend to look paler in flight than in theautumn (as a consequence of wear andfading) and so the primary window orVenetian-blind effect often appears morecontrasting. The underwing also looks paler,more gleaming white and more sparselymarked than earlier in the winter (plate 64).This suggests that at least some underwing-coverts and axillaries are dropped or replacedwith pure white feathers over the winter.

Bare partsThe bill remains black with a variableamount of dirty pink on the basal portion.Close views may reveal a pale tip, which cansuggest that birds have a diffuse, subterminaldark band. There is a tendency for cachinnansto have a more extensively pale bill thanmichahellis during the first winter, but this isfar from diagnostic. The legs and irides are asdescribed for juveniles.

Birds in their first summer (2CY birds in May–September)MoultAt some point in the spring or early summer,2CY cachinnans drop their innermostprimary; this signals the start of their firstmoult of the wings and tail. In large gulls,what was traditionally seen as the first com-plete moult (e.g. Grant 1986) is now regardedas the continuation of a cycle of moult thatstarts in autumn with the partial, post-juv-enile moult (e.g. Howell 2001). Large gulls in

western Europe generally do not moultduring midwinter, so there is a clear breakbetween the end of post-juvenile moult andthe start of wing and tail moult severalmonths later. However, some 2CY cachinnansin the Middle East do moult in winter (pers.obs.). Moult has not been studied intensivelyin cachinnans and it is difficult to be surewhether the species’ post-juvenile and firstcomplete moults are best regarded as twoseparate events or part of the same contin-uous cycle. What is clear is that the identifica-tion of worn, faded 2CY birds in spring doesnot necessarily become easier once they startmoulting – as with both Herring Gull andmichahellis, the pattern on new feathersvaries enormously from bird to bird andtruly diagnostic markings are lacking.

Separation of cachinnans, michahellis andHerring Gull is arguably most difficult duringthe summer moult period. This is because,once in heavy moult, all three species can looktatty, and their jizz is affected by missingfeathers. In Britain, the difficulty of separatingthese three species at this time is com-pounded by the fact that many birders areunfamiliar with the identification of wornand/or moulting first-summers because theyspend more time looking at gulls in thewinter. Importantly, many Herring Gulls lookwhite-headed at this time, so a white-headedappearance is not a particularly useful identi-fication feature.

PlumageNew scapulars grown during the summermay be grey and hence adult-like, but otherbirds show heavy spotting and anchoring; thesame applies to new lesser and mediancoverts. The new tertials and greater covertshave a rather more consistent pattern, and toa degree resemble first-generation ones. Onmany cachinnans the new tertials have aplain, dark brown base and a diffuse, off-white distal portion. The greater coverts gen-erally lack strong barring and anchoring,instead having a rather uniform greyish tomid-brown wash basally and a diffuse palefringe and finely vermiculated tip. As withfirst-generation feathers, there is a pale baracross the greater coverts and often also onthe lower medians. The greater-covert andtertial patterns are unlike those of the most




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65. 2CY (1S) Caspian Gull, Latvia, 17 Aug 2008.This is an example of the more distinctive plumagetype seen in late summer, with some silvery-grey (probably third-generation) mantle feathers andlower scapulars on the right side.The greater coverts are a rather uniform mid brown.The new(dark) second-generation primaries have much more rounded tips than the remaining first-generation ones.This large, elegant bird should not pose any identification problems.

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66. 2CY (1S) Caspian Gull, Lithuania, 10 Sep 2009.

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67. 2CY (1S) Yellow-leggedGull, Spain, 15 Aug 2009.The plumage is quitedifferent from 2CY HerringGull (e.g. many clear greyscapulars) but overlaps tosome degree withcachinnans. Best separatedusing jizz and the pale eye.

68. 2CY (1S) Yellow-leggedGull, Spain, 15 Aug 2009.First-summer michahellisshow bewildering variability.This bird is a rather typicalexample of the moreheavily marked type.

69. 2CY (1S) HerringGulls, Latvia, 14 Aug 2008.Herring Gulls of this ageare variable, but typicallyrather dull and nondescript.The head of 1S HerringGull often lacks streaks, soa white-headed appearanceis shared with cachinnans atthis time of year and is notan important identificationfeature for this age group.

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distinctive michahellis, which have strongblackish crossbars and anchors on otherwisepale feathers, and unlike those of HerringGulls, which have a similar pattern to micha-hellis but more subdued.

By September, it is possible, in verygeneral terms, to recognise two ‘types’ of 2CYcachinnans and michahellis (plates 67 & 68).Advanced birds have extensive, clean greyscapulars, wing-coverts and tertials, while lessadvanced types are heavily spotted andbarred in these areas. The former are verymature-looking compared with 2CY HerringGulls, while the latter share a number of fea-tures with them. With less advanced birds,observers should not be looking for individu-ally diagnostic features; identification shouldbe based on structure, voice and subtleplumage clues.

Bare partsMost 2CYs develop extensive pale areas onthe bill by summer; the colour is highly vari-able, from rather bright pink, through dirtygreyish-flesh to yellowish-grey. The legsappear flesh-coloured, sometimes with a greycast. Eyes are invariably dark-looking (the irisis brown).

Birds in their second winter(2CY/3CY birds duringOctober–April)The moult to second-winter plumage isusually complete by late November (somecomplete in October), at which point allfeathers are at least second generation. Thismoult started in spring/early summer andcontinued through the summer and autumn.Importantly, some of the new feathers gainedearly in this period are not retainedthroughout the second winter. Scapulars,some wing-coverts (most frequently themedians) and some tertials may be moultedagain later in the period; these third-genera-tion feathers are grey and adult-like and con-trast with the remaining brown or barredsecond-generation ones. Essentially, this iswhy late summer 2CYs look rather differentfrom December ones, even though in termsof our standard terminology they are in thesame plumage/age class. The proportion ofadult-type grey feathering is highly variableat this age, but the proportion is typically

greater than in Herring Gull (many of whichare essentially brown in second-winterplumage) and so cachinnans generally lookcleaner, older and more striking (plate 70).

The head and body are normally purewhite, except for a well-defined collar of darkstreaking around the hindneck on some. Themantle and scapulars may be entirely grey,forming a grey saddle, but more typicallysome feathers retain dark shaft streaks and apaler, creamy fringe. The remaining second-generation lesser and median coverts arebasically brownish with creamy or buffishfringes, but dark shaft streaks and small, darksubterminal anchor marks may be apparentin close views. At a distance the greatercoverts look rather uniform brown, forminga dark panel; close views reveal a variableamount of pale vermiculation, which typi-cally becomes more prominent towards theinner feathers. A typical cachinnans has somegrey, third-generation median coverts(matching the scapulars) and some also haveone or two grey tertials which contrast withthe largely brown second-generation ones.Some inner greater coverts may also be grey,contrasting with the brown outer ones.

These feather patterns give cachinnans anoverall impression that is typically quite dif-ferent from Herring Gulls of this age. MostHerrings have many brown, heavily anchor-marked feathers in the mantle, scapulars andwing-coverts and extensive streaking orblotching on the head and body (plate 72).Nonetheless, some do have grey feathers inthe scapulars (plate 73) and, less frequently,in the wing-coverts, so this difference is notdiagnostic. Herring Gull tertials are normallybarred and only rarely show the plain brownpattern typical of cachinnans. Second-wintermichahellis (plates 74 & 75) share the rela-tively advanced appearance of cachinnans,but their legs and bill are typically muchbrighter (often with strong yellow tonesevident) and their wings have much stronger,spotted and notched patterns. They also reg-ularly have fine, sharp pencil streaking on thehead, especially around the eye, and on theneck.

The underwing of second-winter cachin-nans (plate 76) can be gleaming white, butsome retain isolated light brown blotches orbroken bars over the off-white ground

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70. 3CY (2W) CaspianGull, UAE, 7 Feb 2009.The plumage tones areessentially pure white, silverand black, much sharperand cleaner than 2WHerring Gulls.The dark eyecontrasts markedly withthe gleaming white headand the typical grey-fleshtones are evident on thelegs, especially the tibia.Note that the pattern ofthe greater covertsmatches that of 1W birds –uniform dark bases and apale bar along the tips.

71. 3CY (2W) CaspianGull, Latvia, 10 Apr 2009.

72. 3CY (2W) HerringGull, North-east Scotland,8 Mar 2009. As shown bythis and plate 73, theplumage of 2W HerringGulls is extremely variable.Nonetheless, typically theylook much less mature thancachinnans: they lack sharpplumage contrasts,appearing to be a mix ofoff-white and light browntones. Note particularly thepale eyes of these birds.

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73. 3CY (2W) HerringGull, Latvia, 13 Apr 2009.This bird has a rather morecachinnans-like plumagethan many (i.e. it has a greysaddle and upper tertials),but the greater coverts areheavily speckled and it hasextensive diffuse streaks onits head and body; also, itsstocky, compact jizz shouldpreclude any confusion.

74. 2CY (2W) Yellow-legged Gull, Spain, 20 Dec2006. Compared withcachinnans of this age, notethe solid structure, darkstreaking around the eyeand foreneck, and especiallythe heavily marked greatercoverts. As with cachinnans,the advanced plumage of2W michahellis (clean headand body, pure grey saddleand many wing-coverts)makes them look olderthan Herring Gulls of thesame age.

75. 3CY (2W) Yellow-legged Gull, Spain, 8 May2009. By early spring, 3CYYellow-legged Gullsbecome extremely cleanand bright; compared withthe cachinnans in plates 70& 71, note the bright yellowbill/yellow-toned legs andthe strongly notchedcoverts. The eye is clearly rather pale.

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76. 2CY (1S–2W) CaspianGull, Lithuania,10 Sep 2009. Note thewhite underwing, with justa few isolated light brownspots and crescents, andthe small mirror on P10.This bird is just completingits moult into 2W plumage,with P9 and P10 not quitefully grown.

77. 2CY (2W) CaspianGull, Lithuania, 10 Sep 2009.Note the contrasting black-and-white tail,Venetian-blind pattern on the middleprimaries (clearer on thefar wing), grey saddle andclean head.

78. 3CY (2W) HerringGull, North-east Scotland,8 Mar 2009.The overallimpression is of a ratheruniform brown bird,without strong plumagecontrasts.The tail isextensively dark and therump and uppertail-covertsare well marked.

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colour. The axillaries tend to be unmarked,pure white. Second-winter michahellis mostfrequently have contrasting light and darkbrown bands on their underwing-coverts, sothe underwing looks much darker overallthan that of cachinnans; darker birdsresemble graellsii Lesser Black-backed Gull.In flight, the general impression of thecachinnans upperwing is very similar to thatof first-winters, with blackish-brown outerprimaries, secondaries and primary coverts.The pattern on the second-generation innerprimaries is extremely variable, but at leastsome have a strong Venetian-blind pattern –pale, greyish inner webs on the inner pri-maries that contrast markedly with blackishouter webs. This contrast is much lessmarked on most Herring Gulls. On somecachinnans, the inner-primary pattern is lessdistinctive, with light brown rather than greyinner webs; such birds are similar to HerringGulls. Some cachinnans have a diffuse palelozenge on the outer web of the inner 4–5primaries (as for first-generation feathers),but on others the distal part of these feathersis a rather uniform brown.

The rump and tail pattern of cachinnans israther variable at this age (plate 77) but typi-cally the pattern is distinctly different fromHerring Gull’s. In the most striking cachin-nans, the rump, uppertail-coverts and tailbase are unmarked, pure white and contrastmarkedly with a narrow black tail band. Mostfrequently, the tail band has fine black ver-miculation along its basal edge. In others, therump and uppertail-coverts have some iso-lated spots and bars and the tail band is morecoarsely and extensively vermiculated. InHerring (plate 78), the rump and tail baseare, on average, more spotted and barred andthe tail band is browner, deeper and lesssharply defined, so the general appearance ismuch less clean and striking than in cachin-nans. A bird whose tail/rump pattern doesnot differ markedly from Herring Gull’should be checked for other anomalous fea-tures (see part 2).

Most second-winter cachinnans have asmall but distinct mirror on the outerprimary (P10). On some it is small andsandy-grey, on others it is large and whitish,but is generally clearly visible. This feature isextremely useful for separating Herring and

Caspian Gulls, although not wholly diag-nostic: a small proportion (c.1–5%) ofsecond-winter Herring Gulls, particularlyargentatus, have a P10 mirror, while a smallproportion of cachinnans lack a P10 mirror.It is extremely rare for second-winter micha-hellis to have a mirror on P10 (the authorshave seen only one such individual); whenpresent it is very small and usually apparentonly in good quality photographs.

Bare partsThe bare parts of second-winter cachinnansbegin to take on some distinctive hues. Thelegs are invariably a rather sickly grey (‘deadflesh’), compared with the distinctly pink legsof Herring Gulls. The legs of second-wintermichahellis are extremely variable: yellowish,greeny-yellow, flesh or grey-flesh.

The basal two-thirds of the bill usuallybecomes much paler than on first-summers,ranging from greyish-pink on some cachin-nans to dull greeny-yellow on others. Typi-cally, there is a dark smudge near the tip thatextends back along the cutting edge towardsthe base. The pale bill tip is usually muchmore prominent than on first-winters.However, while cachinnans typically have thisbill pattern, the colours and patterns of alltaxa vary markedly: there is much overlapand it is not hard to find Herring Gulls andmichahellis that match cachinnans.

The eye is almost invariably dark-lookingin second-winter cachinnans, contrastingsharply with the white head. Most HerringGulls and michahellis begin to develop palerirides at this age (greyish or brown) and so abird with distinctly pale eyes is unlikely to becachinnans.

Older immature plumages(3CY–5CY birds)Moult and plumage developmentThe second complete moult takes placeduring the summer and autumn of the thirdcalendar-year and brings in new, pure greyfeathers to the mantle, wing-coverts and ter-tials. The third-generation primaries havesmall white tips (unlike first- and second-generation ones), as well as large mirrors onP10 and, most frequently, also on P9. Theouter primaries are otherwise blackish andthe inner ones have adult grey tones. Once

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this moult is complete, birds can be regardedas being in third-winter plumage (plates79–82) and, overall, they show a greaterresemblance to adult than earlier immatureplumages. The upperparts are largely grey,with variable amounts of brown retained inthe tertials and coverts. This plumage isretained over the winter and followingspring/early summer, when the third com-plete moult takes place. This brings fourth-generation primaries and fully adultupperpart tones; normally, the only traces ofimmaturity are dark marks in the primarycoverts and on the bill. The following textdeals primarily with third-winter birds, butprovides some information and illustrationsof fourth-winter individuals.

Once the second complete moult is fin-ished (and third-winter plumage attained),the mantle and scapulars are generally adultgrey, while the coverts are most frequently amixture of grey and creamy-brown. There ismuch variability in the coverts, with somebirds having wholly grey feathers. Brownfeathers tend to be retained more in the mar-ginal and lesser coverts, with the mediansand greaters being contrastingly grey. Thetertials are either all adult-like or have somebrown patches. The outer primary covertsand the alula also retain extensive, blackish-brown marks (plate 82). The secondaries ofsome birds have small, neat brown centresforming a broken bar. The tail pattern isextremely variable. Frequently there is anobvious vestigial tail band created by isolatedblack spots, rather like that of second-winterRing-billed Gull L. delawarensis; such tailbands also occur in michahellis but are veryrare in third-winter Herring Gulls. Somethird-winter cachinnans, however, have awholly white tail.

Although not yet the full adult pattern, thethird-generation primaries of cachinnansoffer useful identification clues. There is abroad, complete black band across P5 andusually some black on P4, either on bothwebs or just the outer. Third-winter birdsthat have limited or no black on P5 areunlikely to be cachinnans or michahellis. Thewhite mirror on P10 can be a useful distinc-tion from michahellis: in terms of size andprominence, the P10 mirror of most third-winter cachinnans matches that of an adult

michahellis (much larger than on third-winter michahellis, which have either nomirror or only a small one). Most third-winter cachinnans also show a white mirroron P9, unlike michahellis (but see plate 84).Third-winter Herring Gulls can also show areasonably large mirror on P9 and P10;argentatus can show a long white tip to P10,with only a small dark subterminal smudge(plate 86). Thus, the patterns on P9 and P10are not diagnostic of third-winter cachinnansand are more useful for ruling out michahellisthan Herring.

On some third-winter cachinnans, themiddle primaries (P6–P8/P9) have black thatextends further up the outer web than theinner; this gives the impression of grey‘tongues’ cutting into the black of the wing-tip, a pattern that develops more strongly inadults. This is very different from argenteusHerring Gulls and especially michahellis(plate 84), both of which show a solid, trian-gular black wedge across the wing-tip. Not allcachinnans have the distinctive tonguedpattern, and so match michahellis andHerring Gull. Both cachinnans and micha-hellis show dark marks on the alula andprimary coverts, which tend to be blackerand more clearly defined than in HerringGull.

The head of cachinnans tends to be cleanwhite, lacking distinct streaking. In autumnand early winter, a relatively neat half-collarof dark streaks is usually visible on the hind-neck and can make cachinnans distinctiveeven at a distance. This streaking wears awayas the winter progresses. Herring Gulls havemore widespread, diffuse and blotchy headand neck streaking. The head streaking of3CY–4CY michahellis in winter is often con-centrated around the face rather thanrestricted to the hindneck.

In the summer of their fourth calendar-year, the third complete moult brings infourth-generation primaries. Once this iscomplete, birds are generally regarded asbeing fully adult, although some retain darkmarkings on the bill and black in the primarycoverts and at the tip of P10. Confidentageing of such birds is difficult, however,since dark marks in the primary coverts andsmall areas of black in the bill are occasion-ally retained well into full adulthood. The




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79. 3CY (2S–3W) CaspianGull, Lithuania,10 Sep 2009.This bird isnear to the end of its moultinto 3W plumage (theouter primaries are notquite fully grown). Anumber of subtle features,used collectively, make 3WCaspian Gulls ratherdistinctive, but as all arefound from time to time inHerring Gulls, none arediagnostic.This bird andthose in plates 80 & 81show ‘lead shot’ eyes,contrasting with a cleanwhite head, greeny-yellowbill and grey-flesh legs.

80. 4CY (3W) CaspianGull, Latvia, 10 Apr 2009.The extent of any brownremaining in the wing ofthis age group is variable –this bird has rather a lot ofdark in the coverts, butnone in the tertials.

81. 4CY (3W) CaspianGull, Latvia, 8 Feb 2010.A bird with soft, grey-brown patterning in thecoverts and some brownremaining in the tertials.All the plumage featuresand bare-part coloursvisible in this bird can befound from time to time in Herring Gulls, so itillustrates nicely the factthat identification of birdsin this age group should besupported by structure and,ideally, voice.

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84. 3CY (3W) Yellow-legged Gull, Spain, December 2006. Birds of this age are variable.This one hasa rather large mirror in P10 but on others it is much smaller or even lacking. It has a clean white tailbut many retain vestigial dark marks.The extensive blackish-brown primary coverts contrast with theotherwise grey upperwing.The black of the primaries forms a solid wedge on the outer wing. Notethe asymmetrical wing-tip pattern – there is a mirror on P9 on the left wing but not the right wing.Such asymmetry is not unusual in gulls; consequently, where a particular feature is critical foridentification, it is always worth making sure that both wings have the correct pattern.

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82. 3CY (3W) Caspian Gull, Lithuania, 10 Sep 2009.The primary pattern of this bird is beginning to takeon some of the features of adults – note the greytongues eating into the black wing-tip.The outerprimary coverts and the alula retain extensive,blackish-brown marks.

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83. 3CY (3W) Herring Gull, North-east Scotland, 2Nov 2008.This bird shows an extensive brown washto its wings, a well-streaked head, has only limitedblack on P5 and (already) a very pale eye. Individuallyand collectively, these features make confusion withcachinnans unlikely. 3W argenteus Herring Gullsregularly show a complete, deep black band across P5,unlike this argentatus, which has isolated dark smudges.So, the presence of a black band on P5 is not a keyfeature at this age. Note that P10 is not yet fully grown.

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fourth-generation primaries of cachinnansare similar to those of adults, with a longwhite tongue on the underside of P10 andgrey tongues eating into the black wing-tipon the upperside of P8–P10.

Bare partsThe third-winter bill has a mix of blackishbrown and paler areas. Black is usually con-fined to the gonys region as a diffuse ‘thumb-print’, with a paler tip and basal third to thebill. Some isolated darker smudges are oftenpresent closer to the base, and many have alittle black bleeding along the cutting edgefrom the gonys. The pale parts of the bill aremost frequently a dull greeny yellow, typi-cally with a strong grey cast. Some haverather more yellow-toned bills. Red is notprominent in the gonys of cachinnans of thisage. The legs are invariably a rather colour-less, dead-flesh grey, compared with thepinker legs of Herring Gulls. The legs ofthird-winter michahellis are usually greeny-yellow or grey-yellow, with some having clearyellow tones; they can, however, occasionallybe dull flesh-coloured as in cachinnans. Theeyes of most cachinnans still look darkbrown, but slightly paler irides may developfrom this age onwards. Most but not allmichahellis and Herrings of this age havepaler (greeny- or greyish-yellow) eyes. It israre for cachinnans of this age to have verypale (cream or yellow) eyes, and such birdsshould be scrutinised closely. Eye-ring colourtones of third-winter birds also begin toreflect those of adults (see below).

PitfallsDespite often looking distinctive, third-winter and third-summer birds have no trulydiagnostic plumage features. In essence, thedistinctive features of younger birds havebeen lost, while the adult wing-tip patternhas not developed sufficiently for it to beconsidered critically important. Identifica-tion should be based on a careful assessmentof structure, in combination with indicativeplumage features listed above, and theabsence of anomalies.

Some cachinnans of this age can be partic-ularly tricky to separate from michahellis.Near-adult michahellis often have dark eyesand smaller individuals can have bill shape

and overall jizz reminiscent of some cachin-nans. Some cachinnans lack grey tongues intheir third-generation primaries and sooverlap with michahellis; however, theyshould have larger mirrors than michahellis.Long call and associated posture are the bestway to separate the more difficult individ-uals.

Experienced gull-watchers are unlikely tomistake third- and fourth-winter HerringGulls for cachinnans, but others should beaware of the problem posed by argentatus.Some late-winter argentatus are clean-headedand share some aspects of the cachinnanswing-tip pattern – with a long white tip toP10 and grey tongues that invade the blackwing-tip. While the irides of most HerringGulls will be rather pale by their third winter,a significant proportion retain dark eyes: aclearly pale eye in a near-adult gull is notgood for cachinnans but a dark eye does notautomatically rule out Herring Gull.

Adults Adult Caspian Gulls are best located in gullflocks by a combination of their peculiar jizz,and relatively dark, small-looking eyes thatcontrast with the white head (plate 86). Iden-tification can then be confirmed by detailedstudy of bill proportions, primary pattern,bare-part colours and upperpart tone. Thefollowing sections deal with these features inturn; plates 87–96 show a selection of adultcachinnans, michahellis and Herring Gulls.

PlumageFig. 2 shows the range of adult upperparttones for cachinnans and similar taxa, at leastin a British context. The figure uses theKodak Grey Scale, a scale that has numberedincrements from 0 (white) to 20 (black). Thescale itself is not reproduced here and mostgull-watchers will not go into the field armedwith a copy of it; fig. 2 simply compares theupperpart tones among the various taxa andshows the degree of overlap between them.

For grey-tone comparisons to be reliable,other taxa should be directly alongside ornearby. Observers also need to be aware ofthe effects of light and viewing angle on theperception of tone. Diffuse sunlight or over-cast conditions are best: strong direct sun-light tends to bleach out subtle differences.

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Another problem is that the grey tone mayappear to change on the same individual as itfaces in different directions relative to theobserver; upperparts tend to look darkestwhen the bird is facing obliquely towards oraway from the observer. Thus, a slightlydarker-backed gull in a flock might just befacing in a different direction from theothers. Any apparent difference should beconfirmed by seeing the bird in a variety ofpositions.

The tone (darkness) of the pure greyupperpart feathers of adult and near-adultgulls is of quite limited value in cachinnansidentification, because it overlaps extensivelywith that of other species. Nonetheless, it canbe useful when looking for the species amongpaler-mantled argenteus in Britain (althoughmost darker birds will turn out to be argen-tatus or michahellis, depending on locationand season). To the practised eye, cachinnanscan be located in flocks of michahellis bytheir subtly paler upperpart tone. CommonGull is usually a close match for cachinnansand, when alongside, can be used as a tonalmarker.

Regardless of tone, there is a subtle differ-ence in colour hue between the upperparts ofcachinnans and Herring Gull, when seen ingood light and in direct comparison. That ofcachinnans is a more neutral, silky grey, withless of a bluish hue than either argentatus orargenteus. The upperparts of michahellis aremore of a slate-grey. The human eye is a per-

ceptive tool and it is certainly possible to seethe differences in colour hue between thesespecies in direct comparison. However,because of differences between how observersperceive and describe colour, it is difficult toarticulate the differences here, in words.

Wing-tip patternAdult cachinnans have a characteristic wing-tip pattern and, particularly when multiplefeatures in the wing-tip are used simultan-eously, this can be a good means of identifi-cation (fig. 1 and plate 49). However, thewing-tip pattern is not truly diagnostic,because of a degree of overlap with argen-tatus Herring Gull.

The outermost primary (P10) of cachin-nans is black, except for a long, pale ‘tongue’on the inner web (grey on the upperside ofthe feather, white on the underside) and along white tip. The black separating thetongue from the white tip is narrower thanthe length of white tip. This pattern is neverseen in michahellis and is very rare in argen-teus; however, it is common in argentatus.The details of the P10 pattern may be diffi-cult to see well on flying birds (except, ofcourse, in photographs) but can often be seenon a standing or swimming bird by viewingthe underside of the folded wing.

Occasional variations in the P10 patternof cachinnans include cases where the paletongue breaks through the black to mergewith the white tip – a pattern typical of



Fig. 2. Upperpart grey tones as represented on the Kodak Grey Scale for cachinnans and similartaxa. Common Gull Larus canus is included as a good tonal match for cachinnans; values are fornominate canus.The michahellis values exclude the Atlantic island populations (atlantis), which havedarker grey tones (from 7–7.5) than Iberian and Mediterranean birds.Values are based on MallingOlsen & Larsson (2003) and Jonsson (1998).

Kodak Grey Scale3 4 5 6 7

main range

exceptional

argenteus

argentatus

cachinnans

canus

michahellis


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85. 5CY (4W) CaspianGull, Latvia, 13 Apr 2009.The extensive dark areason the primary coverts,dark grey wash on theouter webs of P5–P7 andthe black band across thetip of P10 suggest that thisis not a fully adult bird.

86. Adult Caspian Gull(centre left) with HerringGulls, Latvia, 14 Aug 2008.This photograph allowsdirect comparison of jizz,bare-part colours and greytones of the two species.

87. Adult Caspian Gull,Essex, 7 Feb 2009.Thisbird’s eye is at the dark endof the range.

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88. Adult Caspian Gull, Romania, August 2006.The bill is particularly weak and has a fleshy tone toits basal portion.The eye of Caspian Gull is normally described as being dark, but rather few havetruly dark eyes. Most have a speckled iris, which in the field varies in colour from pale amber tobrown, depending on the density of speckling.The eye of this bird is medium amber.

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89. Adult (or near-adult) Caspian Gull, Romania, August 2006.This bird may be a female: it looksrather compact, the bill is not noticeably long and the head is high and rather peaked. Because of thedark eye, many such presumed female cachinnans are surprisingly reminiscent of a Common Gull.Thebroad black band across P5 is visible below the tertials. Brown tones to some greater coverts andtail feathers suggest that this bird may not be fully mature.

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90. Adult Herring Gull,North-east Scotland, 23Nov 2008. As well as thecompact jizz, note theextensive soft streaksacross the head, neck andupper breast, the pale eyeand yellowy-orange eye-ring.This bird has blackacross both webs of P5;this is not uncommon inHerring Gulls.

91. Adult argentatusHerring Gull,Tampere,Finland, 21 Apr 2006. C435was ringed as a pullus inJune 1998 c. 30 km SE ofTampere and represents apotential trap for theunwary. It has a completeblack band across P5, a longwhite tip to P10, yellowylegs and a reddish orbitalring; its bill is ratherslender-based and itsupperparts are a goodmatch for cachinnans.However, the head retainsthe typical bulk of HerringGull, its iris is unmarkedyellow, and the bill has arather sharply curvedculmen and a marked gonydeal angle.

92. Adult Yellow-leggedGull, Portugal, 15 Jun 2005.A typically menacing-looking bird, with a staringpale eye set off against thedeep red orbital ring. In thisspecies, the vivid red of thegonys regularly spreadsextensively onto the uppermandible, unlike the morerestricted gonys spot ofcachinnans and HerringGull.

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93. Adult Herring Gull,North-east Scotland, 28Feb 2009. Note the paleupperparts, black bandacross the tip of P10 andthe limited black on P5.This is a typically compactand short-billed argenteus.

94. Adult Yellow-leggedGull, Spain, 7 May 2009.A typically large, robust andlong-winged bird. Note thebroad black band across P5and the small mirror on P9.

95. Adult Yellow-leggedGull, Spain, 8 May 2009.Theunderside of P10 is visiblehere and shows a triangularwedge (not a squaretongue) extending onlyhalfway down the exposedfeather.The huge billsuggests this is a male.Thegape is bright red, similar intone to the orbital ring.

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Thayer’s Gull L. (glaucoides) thayeri. Anexample of this from Ukraine is shown byLiebers & Dierschke (1997, plate 289), whileCG has seen such birds in Romania (LakeHistria, September 2006). These locationssuggest that the ‘thayeri pattern’ occurs occa-sionally in pure cachinnans, rather than beingindicative of introgression with Herring Gull.Some birds show a small amount of blackwithin the long white tip of P10: of 31 adultcachinnans examined in the hand by Liebers& Dierschke (1997), 11 showed a subterminalblack band (complete or incomplete) acrossthe tip of P10. There is also variation andoverlap among the taxa with respect to theexact shape of the pale tongue, especiallybetween cachinnans and argentatus (Gibbins2003). To reiterate, the P10 pattern is notdiagnostic.

Long, pale grey tongues are also presenton the inner webs of P7–P9 of cachinnansand, collectively, these give the impression ofpale wedges eating into an otherwise blackwing-tip. This pattern is very different from

that of michahellis(which has a solidblack wing-tip) but isseen on many argen-tatus. Black extendsinward as far as P5 oncachinnans and onsome (16%; Jonsson1998) also to P4.Ideally, a candidatecachinnans should havea black band extendingunbroken across bothwebs of P5, typicallyslightly less deep thanthat of michahellis.However, there is con-siderable variation inthe pattern of black onP5 of all the taxa.Around 10% of cachin-nans lack a completeblack band on P5(Jonsson 1998): suchbirds may have isolatedmarks on both theinner and outer websof the feather (plate49) or have black

restricted to the outer web. Herring Gullsmay lack black on P5 altogether (e.g. manyNorwegian argentatus), have black only onthe outer web (frequent in argenteus) or haveblack on both webs. When black is present onboth webs of P5 in Herring Gull, it may be asan isolated black spot on each (usually largeron the outer web), or as a complete band(plate 90). When present, the band is usuallymuch narrower than on michahellis, but itmatches many cachinnans. Black on bothwebs of P5 is a surprisingly common featurein eastern Baltic populations of Herring Gull(Malling Olsen & Larsson give a value of30%), so these birds are a real cause of confu-sion. Overall, the variability in P5 patternmeans that it is difficult to give definitive cri-teria regarding its value in identification. Likecachinnans, Herring Gulls can have blackextending inwards as far as P4, though this israre.

Some have argued that eastern andwestern populations of cachinnans differ withrespect to primary pattern (e.g. Stegmann

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96. Adult Herring Gull L. a. argentatus, Finland, 30 Mar 2007.The P10pattern of this bird is similar to that of cachinnans – it has a long greytongue, visible here on the underside, and a long white tip to the feather.Coincidentally, it also has a red orbital ring and a dark-looking eye, bothalso features of cachinnans. Its bill, however, is robust and it has verylimited black on P5.This bird illustrates the problems posed by someBaltic argentatus; careful assessment of the full range of features is neededfor correct identification.

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1934). Adults from eastern populations nor-mally have a less extreme wing-tip pattern,where the long white tip of P10 is regularlyinterrupted by small black spots on each web,sometimes merging to form a subterminalband. A significant proportion show black onP4 (50%; Jonsson 1998). Compared withwestern birds, eastern cachinnans may alsoshow shorter pale tongues invading the blackof the upperwing, but these still break up theblack of the outer primaries in a way thatmichahellis never shows. More research isneeded to determine whether eastern andwestern cachinnans deserve formal subspeciesstatus.

Head patternThe head of adult cachinnans normallyappears unmarked (plate 87). Any streaks areextremely fine, often confined to the lowerrear neck, and usually only apparent at closerange for a limited period in autumn (plate88). In michahellis, streaking is also usuallyapparent only in the autumn but is concen-trated around the face and ear-coverts. Onaverage, this streaking is clearer than shownby cachinnans at this time. Streaking disap-pears in late autumn, as feathers wear. Fromearly autumn to mid/late winter, the vastmajority of Herring Gulls show a variable butusually obvious degree of dusky streakingand/or blotching on the head and neck (plate90). There are exceptions and it is possible(though uncommon) to find clean-headedargenteus and argentatus before January, justas it is possible to find the odd Black-headedGull Chroicocephalus ridibundus with a fullhood in midwinter.

Bare parts Outside the breeding season, the bill ofcachinnans is normally a rather weak,greenish-yellow, fading to grey-green basally.There are frequently some dark marks (smallspots or crescents) in the gonys, while the redis usually less bright than for either micha-hellis or Herring Gull. Thus, in general, thebill of cachinnans in winter stands out asbeing duller than that of the other species.However, as many argentatus have washed-out, greeny-yellow bills in winter, bill colourand pattern is merely a supportive feature.

The bill becomes a richer yellow in late

spring and, during the breeding season thebill coloration of cachinnans overlaps withthat of Herring Gull. Neubauer et al. (2009)argued that, unlike the orbital ring (seebelow), bill tones do not differ consistentlybetween cachinnans and Herring Gull inbreeding plumage. The bill of cachinnans isdistinctly duller than the bright, orange-toned bill of michahellis; moreover, the redgonys spot of michahellis is extremely brightand regularly spreads extensively onto theupper mandible.

In the field, most adult cachinnans appeardark-eyed; in fact, the iris is not wholly dark,but peppered by dark brown spots.Depending on the density of these spots, theiris may appear dirty amber-yellow or uni-formly dark brown, but never completelyblack. Eye colour varies enormously incachinnans: Jonsson (1998) suggested that c.75% of adult cachinnans appear ‘medium- todark-eyed’ in the field, whereas Liebers &Dierschke (1997) found that 48% of birds inone Ukrainian colony and 62% in anotherwere ‘pale-eyed’. Much depends on how ‘dark’is defined. Most birds do look darker-eyed inthe field than typical Herring Gulls or micha-hellis and truly pale (clean yellow) eyes arerare in cachinnans (<10% Jonsson 1998;2–5% Hannu Koskinen pers. comm.). Notealso that some apparently adult HerringGulls have dark peppering in the iris andsome look genuinely dark-eyed in the field(plate 96); anyone checking large numbers ofHerring Gulls should expect to find dark-eyed birds with moderate regularity.

The orbital ring of cachinnans varies frompale orange to red (Liebers & Dierschke 1997;Neubauer et al. 2009). That of Herring Gullvaries from yellow (typical argenteus),through pure orange to orangey red; that ofsome Baltic argentatus looks deep red andthus approaches michahellis. Orbital ringcolour in Herring Gulls has been shown todiffer among birds breeding in the samecolony (Muusse et al. unpubl.). Thus, whileorbital-ring colour is a useful feature forcachinnans (orange to red is acceptable,yellow is a problem), it is merely one of anumber of features that combine to make thespecies distinctive but which are not individ-ually diagnostic. Liebers & Dierschke (1997)reported a correlation between iris and




orbital ring colour – pale-eyed cachinnanshaving pale orange orbital rings and dark-eyed birds having redder orbitals – and thisrelationship is clearly worth further study.

The leg colour of adult cachinnans variesseasonally and individually. In winter, the legsare typically pale, greyish-flesh; some have aweak, greenish-yellow tint. In spring and earlysummer, the legs of many adults become dis-tinctly brighter and yellowish. The proportionshowing truly yellow legs during the breedingseason is uncertain and may vary among pop-ulations and even from year to year (perhapslinked to diet). The leg colour of an indi-vidual bird can vary during the course of thebreeding season, probably as a function ofphysiological condition (Neubauer et al.2009). There is complete overlap in leg colourbetween cachinnans and the Herring Gulls ofthe eastern Baltic (from pure pink to lemonyellow) so this feature is of limited value.However, cachinnans rarely matches the richyellow of the legs of michahellis.

PitfallsThe most likely problem is confusion with aHerring Gull from the eastern Baltic. Theseare quite unlike the Norwegian argentatusthat we are familiar with in the UK and canhave upperpart tones, bare-part colours andwing-tip patterns that are virtually identicalto those of cachinnans. The potential for con-fusion is increased by the fact that theseargentatus may look slightly longer-winged,longer-legged and longer-billed than argen-teus (although less obviously so than cachin-nans). The occasional dark-eyed bird cancreate real problems.

Concluding remarksThe aim of part 1 of this paper has been todescribe the appearance of typical CaspianGulls. The birds featured in the plates are allrather typical and should not pose any iden-tification problems. Variability is a feature oflarge gulls, however, and observers shouldnot expect all cachinnans to look identical.Nonetheless, there is what might be regardedas normal or typical variation (that outlinedabove) and that which is extreme or atypical.In part 2 we shall deal with the extremes anddiscuss birds that sit in the overlap zonesbetween the species. We shall also consider

hybrids; this is a very real problem given thathybridisation is occurring in Poland, forexample, and that hybrids originating therehave been recorded in Britain. Beforebecoming embroiled in debates about themore difficult individuals, it is importantthat birders are familiar with the identifica-tion of typical birds. We hope that part 1 hasprovided this familiarisation.

Acknowledgments

The authors would like to thank Nic Hallam, HannuKoskinen, Ian Lewington and four anonymousreviewers, whose insightful comments greatlyimproved this manuscript.We are also grateful to RuudAltenburg, Steve Ar low, Hannu Koskinen, MikeLangman and Pim Wolf for sharing and allowing us touse their photographs. A number of birders sharedtheir knowledge and experience of cachinnans duringthe preparation of this paper ; we especially thankRuud Altenburg, Hannu Koskinen, Mars and TheoMuusse and Visa Rauste in this regard. Dmitri Mauquoykindly produced fig. 1.

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Collinson, J. M., Parkin, D.T., Knox,A. G., Sangster, G., &Svensson, L. 2008. Species boundaries in the Herringand Lesser Black-backed Gull complex. Brit. Birds101: 340–363.

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Gruber, D. 1995. Die Kennzeichen und das Vorkommende Weißkopfmöwen Larus cachinnans in Europe.Limicola 19: 121–127.

Howell, S. 2001.A new look at moult in gulls. Alula 7:2–11.

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Klein, R. 1994. Silbermöwen Larus argentatus undWei‚kopfmöwen Larus cachinnans auf Mülldeponienin Mecklenburg – erste Ergebnisse einerRingfundanalyse. Vogelwelt 115: 267–285.

Leibers, D., & Dierschke,V. 1997.Variability of fieldcharacters in adult Pontic Yellow-legged Gulls. DutchBirding 19: 277–280.

—, Helbig,A. J., & de Knifff, P. 2001. Geneticdifferentiation and phylogeography of gulls in theLarus cachinnans-fuscus group (Aves:Charadriiformes). Molecular Ecology 10: 477–2462.

Malling Olsen, K., & Larsson, H. 2003. Gulls of Europe,Asia and North America. Helm, London.

Neubauer, G., Zagalska-Neubauer, M. M., Pons, J-M.,Crochet, P-A., Chylarecki, P., Przystalski, A., & Gay, L.2009.Assortative mating without completereproductive isolation in a zone of recent secondary

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contact between Herring Gulls (Larus argentatus)and Caspian Gulls (L. cachinnans). The Auk 126:409–419.

Small, B. 2000. Caspian Gull Larus cachinnans in Suffolk

– identification and status. Suffolk Birds 49: 12–21.Stegmann, B. K. 1934. Ueber die Formen der Großen

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Chris Gibbins, 2 The Steadings, Newtyle Farm, Drums, Aberdeenshire AB41 6ASBrian J. Small, 78 Wangford Road, Reydon, Southwold, Suffolk IP18 6NXJohn Sweeney, 33 McLean Place, Paisley, Renfrewshire PA3 2DG

The British Birds Rarities Committee is sponsored by Carl Zeiss LtdChairman

Adam Rowlands, East Walks Bungalow, Minsmere RSPB Reserve, Westleton, Suffolk IP17 3BY Secretary

Nigel Hudson, Post Office Flat, St Mary’s, Scilly TR21 0LL;e-mail [email protected]

BBRC members Chris Batty, Chris Bradshaw, Lance Degnan, Paul French, Martin Garner,Nic Hallam, James Lidster, Richard Millington, Mike Pennington, John Sweeney

Archivist John Marchant • Museum Consultant Brian SmallSummariser and RIACT Chairman Reg Thorpe • RIACT Secretary Peter Kennerley

97. Unidentified adult gull, Lithuania, 10 Sep 2009.This striking bird has a confusing mix ofcharacters. Its dark iris, red orbital ring and upperpart grey tones match cachinnans. However, its legs and bill are extremely bright for cachinnans, especially at that time of year, and the red of thegonys spreads extensively onto the upper mandible; it also has a rather well-streaked head for typicalcachinnans.The bill and leg colours are reminiscent of michahellis, but any thoughts of that species aredispelled by the ‘thayeri pattern’ visible on the underside of P10 (and of course the dark eye is wrongtoo).While the P10 pattern matches some argentatus Herring Gulls, the leg, bill and eye colours makethis option seem unlikely. Is it simply an extreme cachinnans, should it be considered a likely hybrid oris it best left unidentified? Fascinating birds such as this are the focus of part 2 of this paper.

Chris

Gib

bins


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Appendix 1. Summary of key differences between typical Caspian Larus cachinnans,Yellow-leggedL. michahellis and Herring Gulls L. argentatus. It is important to note that these highly simplifiedstatements should be read in conjunction with the main text. Features are given for each age groupand in approximate order of importance/value for field identification; shaded blocks indicate thereliability of individual features, as detailed in the key.

Diagnostic – not found/known to occur in other species

Extremely indicative – should not be used in isolation, but any bird showing this feature plus one

or two others should prove to be cachinnans

Indicative – very useful, but only in conjunction with other features

Supportive – should be used only to support details of other, more reliable, features

Of no real value – overlaps completely with other species or is perhaps based on misconception

Structure and Caspian Yellow-legged Herring Commentsbehaviour (cachinnans) (michahellis)

Rapid, nasal laughingcall with wings raisedand head vertical(90º)

Deep, guttural, singleand clearly separatednotes delivered moreslowly thancachinnans, withwings closed and headraised to 90°

Call structure similarto michahellis but lessguttural and pitchhigher; delivered withwings closed and headraised to 45°

Long calland long-call posture

Bill shape

Together, long call and associated postureare diagnostic; i.e. abird with correct calland long-call postureshould prove to becachinnans. All otherstructural features vary individually andbetween the sexes,but assuming that keyplumage featuresmatch, then non-calling birds can beidentified using headand bill shape; otherstructural features vary and so are lessimportant

Typically long, slimand evenly tapering;little or no expansionat gonys

Deep and long inmales; females overlapwith Herring. Curvesstrongly at tip withmarked gonys angle

Unremarkable,but with clear gonys angle

Head shape Generally pear-shapedand snouty; small forbody. Some (females?)can have highrounded crowns andsome larger birds(males?) have square,more solid heads

Head typically largeand square. Femalesoverlap with Herringand Lesser Black-backed. Rarely assnouty as cachinnansbut some are similar

Unremarkable: evenshape, neither snoutynor square, but someargentatus can matchmale cachinnans

Leg length Typically long andthin but can lookunremarkable in some (females?)

Can overlap in lengthwith cachinnans, butnormally thicker andmore robust-looking

Relatively short,robust-looking

Body shape Very attenuated rearend; ventral bulgeclear on many

Attenuated but ventralbulge lacking or lesspronounced

Relatively short rearend, lacking ventralbulge

Tertial step Normally lacking Can be clear orlacking

Usually pronounced

Stance Often upright, withhigh chest; bill helddownward whenresting

Normally morehorizontal, but whenalert can look verycachinnans-like

Normally morehorizontal

Varies hugelydepending on what thebird is doing so is oflimited practical value




Appendix 1. continued

Juv and Caspian Yellow-legged Herring Comments1st-winters (cachinnans) (michahellis)(Aug–Apr)

Normally distinctlypale; appears silvery or creamy-white atdistance on the moststriking birds

Dark and heavilybarred but (rarely) canoverlap with darkercachinnans

Dark, though moreuniform thanmichahellis

Underwing

Striking white rumpand tail, with relatively narrow black tail band

Very similar tocachinnans

Browner, deeper andless clear-cut tail band.Less contrast betweentail band and the moredensely marked rumpand tail base

Tail andrump

Pale grey groundcolour (silvery) inclassic birds, eachfeather with a simpledark shaft streak andnarrow subterminalanchor. Some aremore heavilypatterned

Strongly marked, withheavy anchor patternand heavy blackish-brown bars acrossbasal part of eachfeather

Variable; most havepattern similar tomichahellis, but withcrossbarring andsubterminal anchorsweaker

Second-generationscapulars

Cachinnans is distinctfrom Herring but verysimilar to michahellis

Uniform dark baseand pale terminal areaforming clear bar,like Nike ‘swoosh’.Pale fringes simple,lacking strong notches

Typically heavilynotched, particularlyon inner feathers; butextremely variable andsome have simplefringes that resemblecachinnans

Extremely variable,but normally wellnotched across allcoverts; birdsmatching cachinnansare extremely rare(<1/1,000)

Greatercoverts

Typically clean-looking (whitish) withminimal streaking.Often has neat halfcollar of fine streakingaround rear neck

Overlaps withcachinnans, but morefrequently has obviousdark eye mask and lesspronounced collar

Normally extensivelycovered with diffusestreaks and blotches

Head andbody colour

Soft, greyish-brown Dark, chocolatebrown, withcontrasting pale areas

Mid brown,intermediate betweenthe other two

Colour ofupperparts(juvs only)

Less prominent thanHerring, slightly moreso than michahellis.Often with Venetian-blind pattern. Palelozenge-shapedpatches frequentlypresent on outer websnear tips of P2–4/5

Inner webs of innerprimaries onlyfractionally paler thanouters, so virtually nowindow. Generallylack pale lozenges onP2–4/5

Prominent window,with complexpatterning on feathertips of P1–4/5

Innerprimarywindow

Extremely useful butshould not be used in isolation


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1st summers Caspian Yellow-legged Herring Comments(Apr–Sept) (cachinnans) (michahellis)Structure, call and call posture are especially critical during this period, as wear, moult and individual variation inthe patterns on newly arriving second- and third-generation feathers make plumage features of limited value.

Whiter than the otherspecies, althoughmoult may produce a blotchy pattern.

Extremely variable,some with variegatedpattern of light anddark.

As michahellis, but less contrasting

Underwing

Second-generationfeathers in typicalbirds have uniformdark base and paleterminal bar.

Second-generationfeathers usually wellmarked withcontrasting light anddark bars. But, somelike cachinnans, otherslike Herring Gull

Pattern oftenintermediate betweencachinnans andmichahellis, butindividuals can matcheither. Normally morebarred than cachinnans

Greatercoverts

Mantle andscapulars

A useful averagedifference, but there isoverlap between thespecies so this featureis not diagnostic

Extremely variable.Some acquire a highproportion of adult-type grey feathers,others show mostfeathers with darkanchors

Extremely variable.Many acquire mainlypure grey adult-likefeathers while othershave boldly patternedfeathers, withcontrasting anchors

Grey feathers are rareon birds of this age:most acquire third-generation featherswith a pattern of mid-brown bars on acreamy background

A useful feature forseparating HerringGull from the othertwo species.

Tertials Typically shows ablackish basal third to new second-generation tertials,with diffuse pale tip(reminiscent of first-generation feathers)

Often strongly barred(matching greatercoverts) but othersmatch the simplerpattern of cachinnans

Most have an irregularbarred pattern onsecond-generationtertials, but patternusually weaker thanon most michahellis

Each species has atypical pattern (i.e. apattern shown by most birds) but thereis enough variation to limit the value ofthis feature

Head andbody

Variable; many areextremely white,but others can havefine streaks on faceand rear neck

As cachinnans Wear and fading canmake some look muchpaler than first-winterbirds, but rarely dothey look as clean astypical cachinnans





2nd winters Caspian Yellow-legged Herring Comments(Oct–Apr) (cachinnans) (michahellis)Overall, the clean white head and body and the extensive grey in the mantle and wings make typical cachinnans ofthis age look older and more striking than typical second-winter Herring. However, this plumage pattern overlapswith michahellis. Despite the very arresting appearance of some birds, no single feature is diagnostic, soidentification should be based on multiple character traits.

Strong contrastbetween pale greyinner webs andblackish outer webs,creating Venetian-blindeffect on some birds

Lacks Venetian-blindpattern

Lacks Venetian-blindpattern

Innerprimaries

Venetian-blind patternnot present on allcachinnans, but whenpresent it is a veryuseful feature

Normally strikinglywhite

Contrasting dark barsover whitish basecolour

Typically rather dirty-looking, with muchbrown spotting

Underwing

Striking white rumpand tail contrastingwith black tail band

As cachinnans Tail band thicker,browner and lessclean-cut; less contrastwith tail base and rump

Rump andtail

Pattern of cachinnansdistinct from typicalHerring, but overlapswith michahellis

In most, the scapularsare dominated byclean, grey feathers,with limited brown,but some retain morebrown/spottedfeathers

As cachinnans Variable mixture ofgrey and brownfeathers, butpredominant tone isusually brownish.Often heavily markedwith brown bars.Small proportionshow extensive greysaddle

Mantle andscapulars

Generally, the scapularpattern (coupled withcoverts and whitehead) makescachinnans look olderthan Herrings of thisage

Dark brown Normally pale-lookingbut dark on some

Normally pale butdark on sizeableproportion

Eye colour A pale eye wouldsuggest that a bird isnot cachinnans, but allthree species can showdark eyes at this age


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Older Caspian Yellow-legged Herring Commentsimmatures (cachinnans) (michahellis)(3rd-/4th-winters)At this age several features need to be used in conjunction as individually they are of only limited value. No onefeature is appreciably more valuable than the others.

Should show a thick(deeper than wide),unbroken, black bandon P5; many also haveblack on P4

As cachinnans May show a completeblack band on P5 but rarely as deep as in cachinnans andmichahellis. Black onP4 less frequent thancachinnans

Black bandon P5 & P4

Birds of this agelacking a completeblack band on P5 are unlikely to becachinnans ormichahellis

Most have extensivesharp black streaks,contrasting withotherwise grey wing

As cachinnans Streaks browner,diffuse and contrastmuch less with rest ofupperwing, which,especially inargentatus, can retaina brownish tinge tothe grey

Primarycoverts

Useful for separatingHerring from the other species, butoverlap betweencachinnans andmichahellis

Many have patternthat mirrors adult’s,with grey tongueseating into the blackwing-tip; others lackthis and so the wing-tip resembles that ofthe other two species

Lacks tongues and soappearance is of anextensive and solidlyblack wing-tip

Less extensive blackthan michahellis, butargenteus lack tongues;some argentatus showtongues but these arenormally lesscontrasting than oncachinnans

Primarytongues

The presence oftongues eliminatesmichahellis, but otherfeatures needed to rule out argentatus

A neutral, CommonGull L. canus grey, butoften looks moresilvery at this age andso can appear to havepaler upperparts thanadults

Averages slightlydarker thancachinnans: toneranging fromCommon Gull toKittiwake Rissatridactyla grey

Paler in argenteus, butcachinnans sits withinthe range ofargentatus. Slightbluish tint not seen inthe other species

Upperpartgrey tone

Useful for locatingcachinnans amongargenteus; cachinnanscan be picked out inmichahellis flocks bytheir subtly paler tone

Most frequently haslarge mirror on P10and often a small oneon P9

No mirror, or only asmall one on P10

L. a. argentatusoverlaps withcachinnans; argenteustypically has smallermirrors

Primarymirrors

Useful only forseparating cachinnansfrom michahellis

Grey flesh Normally strongyellow tones, or atleast greeny-grey

Flesh or pinkLeg colour

Looks dark in the fieldin most

Normally pale (greeny,yellow or greyish-white) but some retaindark eyes

As michahellisEye colour Overlap means this isof no real value at thisage, but a very pale-eyed bird is unlikely to be cachinnans

Pale yellow, often witha weak greenish tinge;variable darkmark/smudge behindbill tip

Often rather bright,especially in summer:yellowish with blackin gonys and somescarlet red. Othersduller and overlapwith other species

Pattern normallyintermediate, but canmatch either

Billcolorationand pattern

Overlap complete,but typical cachinnanshas dull bill with darkgonys smudge





Adults Caspian Yellow-legged Herring Comments(cachinnans) (michahellis)

Combination of longwhite tip to P10, palegrey tongues eatinginto black of P7–P10,clear and sharplydemarcated whitetongue visible on theunderside of P10,and (in most) solidblack band on P5 isextremely indicative

Lacks tongues andonly rarely has fullywhite tip to P10;broad black bandacross P5

Typical argenteus hasblack subterminal baracross P10 (not a longwhite tip), black ononly the outer web ofP5, a short diffusetongue on theunderside of P10, andno tongues on theupperside of P7–P10;however, someargentatus overlapcompletely withcachinnans

Wing-tippattern

Primary patterndiagnostic betweenCaspian and Yellow-legged and betweenCaspian and argenteusbut not betweenCaspian and argentatus Herring

Typically (>50%)dark-eyed with aneye-ring that rangesfrom pale orange tored; pale eyes are notuncommon, however

Pale yellow (evenwhitish) with deep red(scarlet) orbital, givinga staring, aggressivelook

Pale yellow withyellow (argenteus) tored (some argentatus)orbital

Colour ofeye andorbital ring

Although eye colour is key to givingcachinnans theircharacteristic look,apparently adultYellow-legged andHerring Gulls canretain dark eyes, whilepale eyes can appeardark in poor light or at a distance (goodviews are essential)

Highly variable: inwinter, the majorityhave greyish-flesh legs;in breeding seasonmany are weaklyyellowish, somestronger yellow

Typically a rich yellow,sometimes with a faintorange element (likegraellsii) lacking inmost Baltic argentatus

Variable: flesh-pink in argenteus, butargentatus range fromflesh-pink throughgrey-yellow to brightyellow

Leg colour A bird in midwinterwith bright yellow legs is unlikely to becachinnans, butotherwise leg colour is of limited value

In winter, typicallyduller (greeny-yellow)than for other species,reddish gonys weakand restricted; insummer, overlaps withHerring, less brightthan michahellis

Bright yellow with astrong red gonys spot,that frequentlyextends onto theupper mandible

Overlaps withcachinnans insummer; in winter,most argenteus havebrighter bills thancachinnans, butargentatus overlap

Billcoloration

As with leg and eyecolour, while there is a typical cachinnans‘look’, there is alsocomplete overlap with Herring Gull


from the rarities committeeâ€™s files identification of caspian gull

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