avian biogeography

Avian biogeographyAvian biogeography

CHAPTER 2CHAPTER 2

Why study biogeography of birds ?Why study biogeography of birds ?

Different aspects of avian biology addressedDifferent aspects of avian biology addressed

• how have new bird species arisen ?

• how did they come to be distributed in the way they are ?

• how are patterns of distribution and diversity maintained ?

• how does their (behavioural) ecology differ between regions ?


Birds as ecological modelBirds as ecological model

• evolutionary relationships well understood



Irwin et al. 2001. Speciation in a ring. Nature 409: 333-337




• geographical pattern of morphological variation well studied

• distributional patterns well mapped



Opisthocomus hoazin




• geographical pattern of morphological variation well studied

• distributional patterns well mapped

• high mobility allows presence and radiation on remote islands

• very strong seasonal migration

• large-scale ringing data

Continental birdsContinental birds


• level of distinctiveness of land-masses reflects both their relative position and geological history (tectonics, duration and degree of isolation, opportunities for separate evolution)


Geological time scale and break-up of Gondwanaland

Archaeopteryx – ca 150


• level of distinctiveness of land-masses reflects both their relative position and geological history (tectonics, duration and degree of isolation, opportunities for separate evolution)

• combination of present distribution patterns along with palaeo-geological evidence

• 19th century: global system first developed for passerine birds, then modified by Alfred Russel Wallace (1876) to apply to animals in general

• crucial barriers are seas, deserts, mountain ranges, climatic-vegetation ecotones


Main biogeographical regions of the world


Main biomes (vegetation zones) of the world


• proportions of families, genera and species shared depend on the effectiveness of the barriers and the distances between the regions, both now and in the geological past

• the longer an area has been isolated, the higher the taxonomic rank of its endemics

Palaearctic regionPalaearctic region




• 46 mil km²; more than twice as big as any other region

• within each type of habitat, more species at E than W end of Eurasian land-mass, due to the greater severity of the glaciations in the west



• 46 mil km²; more than twice as big as any other region

• within each type of habitat, more species at E than W end of Eurasian land-mass, due to the greater severity of the glaciations in the west

• marked seasonality



• Atlantic has proved an effective barrier to range extension in landbirds: Northern wheatear, Cattle egret, Little gull, Fieldfare, Spotted sandpiper, Wilson’s phalarope



• Bering Strait: dry land during glacial periods (10.000 y ago) and holds series of islands (stepping stones): Yellow wagtail, Northern wheatear, Arctic warbler, Snow goose, Grey-cheeked thrush, Yellow-rumped warbler (tundra or boreal forest)




• Mediterranean Sea ca 5 mil y (early Pliocene); less effective barrier with many islands: North African species are Palaearctic in affinity (e.g. 165 species breeding but not extending in sub-Saharan Africa): Dupont’s lark, Moussier’s redstart, Tristram’s warbler, Algerian nuthatch supplemented by Sub-Saharan species (White-rumped swift, Black-crowned tchagra)



• birds of N and C Sahara predominantly Palaearctic, mainly at oases (Cirl bunting, Eurasian spoonbill, Little owl) supplemented by Afrotropical species extending N (Small buttonquail, Red-knobbed coot, Little green bee-eater, Senegal thick-knee, Nile valley sunbird)



• mountainous southwest Arabia usually included in Afrotropical Region, while birds of Persian Gulf and Iran predominantly Palearctic



• mountainous southwest Arabia usually included in Afrotropical Region, while birds of Persian Gulf and Iran predominantly Palearctic

• at least 937 landbird species breed regularly in the Palearctic Region, which is a low number and a low level of endemism (no endemic families, 9% genera and 47% species restricted to the region)



• localised endemics at Madeira, Canary Islands, Cyprus, Azores, Corsica and Caucasus



• within both regions, proportion of shared species increase N, resulting in a Holarctic distribution: e.g. Red crossbill, Northern goshawk, Common goldeneye (boreal forest); Rock ptarmigan, Gyr falcon, Lapland longspur (tundra); King eider, Sabine’s gull, Glaucous gull (arctic ocean)



• closely related species point towards recent divergence in geological time (ancestral homes differ between pairs); e.g 0.5 mil y for Northern harriers; 4.3 mil y for Eagle owls; 7.9 mil y for Pygmy owls


Ecologically equivalent and closely related species in Eurasia and North America



• some families poorly represented, such as 7 and 2 species of Kingfishers (86 species) and 1 and 2 species of Parrots (360 species)

• examples of poorly represented Old World families in North America are Warblers, Shrikes and Larks, and the representatives are often more closely related to eastern Asian species

• examples of poorly represented New World families in Eurasia are Wood warblers; Tyrant flycatchers and Vireos



• migrant passerines in both regions are phylogenetically more different from each other than the residents and short-distance migrants

• suggests that many long-distance passerine migrants (mainly insectivorous warblers and flycatchers) derived from essentially tropical families

• not true for shorebirds and waterfowl


Indomalayan (Oriental) regionIndomalayan (Oriental) region



• 9.6 mil km²; mainly within the tropics; northern border (Himalayas) corresponds with climate-vegetation ecotone

• includes Indonesian archipelago, Philippines, Borneo, Sulawesi, Sumatra, Java and Bali

• transition zone between Oriental and Australian Regions called Wallacea; 120 m lower sea level during glaciations, when Sunda shelf was connected to continental Asia; deep water channel east of Sunda shelf contains oceanic islands such as Moluccas and Lesser Sundas


Boundary between Indomalayan and Australasian faunas



• not known till when Philippine Islands were attached to SE Asia, Sulawesi may never have been connected to mainland Asia; more avian affinities with Philippines and Lesser Sunda Islands than with Sumatra and Borneo

• 3rd richest Region with 1697 species; 3 endemic families (Leafbirds, Asian frogmouths and Bearded bee-eaters), 129 endemic genera, 1184 endemic species (70%)



• major wintering area for east Palaearctic breeding birds

• shares most families (but not species) with Africa, probably because of connection by broad stretch of tropical habitats through Middle East till Miocene (often considered single Palaeotropical Region for plants)



• at family level both regions share Broadbills, Bulbuls, Sunbirds, Weavers, Honeyguides

• family Phasianidae particularly well represented, and centre of radiation for Pittas, Laughing thrushes, Drongos, Flowerpeckers



• richness partly results from fusion of 3 separate faunas originating at different land-masses, and infiltration from at least 2 others; some regions isolated for long periods; inclusion of many islands (e.g. Philippines 7100 islands) with high endemism (Philippines: 43% of 403 breeding species endemic; Sulawesi 36% of 247 species)

• strong difference between SE part of Eurasia and rest of land-mass due to effectiveness of Himalayan chain and Tibetan plateau, abundance of islands, and tropical forest belt


Afrotropical (Ethiopian) regionAfrotropical (Ethiopian) region



• mainly tropical region; south of the Sahara and Madagascar, Comoro, Seychelles and Mascarene Islands (islands sometimes separated as a distinct Malagasy Region)

• northern border poorly defined across Arabia

• ca 21 mil km² (1.25 mil south of tropics)



• main vegetation types run in latitudinal belts, becoming more arid and open north- and southwards from the equator, but basic pattern is complicated by topography

• markedly seasonal climate with distinct dry and wet seasons



• although similar in latitude as Neotropical Region, it contains less than half as many landbird species (ca 1950 regional breeders), partly because tropical and montane forest cover much smaller areas and high arid plateaus are more extensive



• among passerines, Weavers, Waxbills, Starlings, Larks, Shrikes and Sunbirds are especially well represented. Also rich in Francolins, Bustards, Barbets, Honeyguides and Cisticola’s, but poor in Parrots and Woodpeckers.



• both species of Oxpecker have evolved in close association with large herbivorous mammals



• 11 endemic families of mainland Africa and 6 of Malagasy mostly contain small numbers of species, and some are represented among fossils from Europe and North Africa



• main centres of endemism: Ethiopian massive, Cameroon Mountains, East African Mountains, Somali and Namibian arid zones, Gulf of Guinea Islands (Principé, São Tomé)



• hard to decide in which direction colonization took place, but some seem certain: e.g. two African Pittas, four African Broadbills, eight African Drongos (from SE Asia); three African Wagtails, Longbilled pipit (from Eurasia); Cisticola juncidis, Ploceus weavers, Estrildinae (to SE Asia)

• enormous influx from Palaearctic migrants (about a third of all species from that region), some species occasionally breed in Africa



• Malagasy subregion: Madagascar fourth largest island on earth, ca 400 km from Africa; thought to have broken away from Gondwanaland as a unit with India > 100 mil y ago, then separated from India 80-85 mil y ago.



• some species such as the extinct Elephantbirds may date back to this period; other species may have arrived later by cross-water flights



• various levels of endemism (from families to subspecies) attest to the continuation of the colonization process over long period of time.

• Some part of the avifauna is relictual, e.g. fossil birds similar to Madagascan ground-rollers from North-America



• Avifauna of Madagascar relatively poor (198 breeding landbird species), but about 25% of the genera and >50% of species endemic.

• Small average number of species per genus implies low rate of recent speciation (or immigration) or high rate of recent extinction (low speciation:extinction ratio). One adaptive radiation has given rise to diverse range of songbird species, resembling bulbuls, babblers and warblers; another has given rise to 14 species of Vanga shrikes (classified in 12 different genera)

• Mascarenes, Seychelles and Comoros derived birds mainly from Madagascar (sharing 22 landbirds); many flightless species went extinct (e.g. Dodo)


Australasian regionAustralasian region



• comprises eastern Indonesian Islands, New Guinea, Australia, New Zealand and neighbouring Pacific Islands;



• total area ca 0.9 mil km²; large proportion semi-arid or arid; 40% in the tropics; Australia is the dries continent; bird movements are mainly constrained by expanses of desert rather than by mountain ranges



• Australia has been physically isolated for more than 55 mil years, giving rise to a unique fauna derived from Gondwanan heritage; repeatedly connected to New Guinea and Tasmania, most recently 10.000 years ago; relatively little migration to and from other regions

• lack of glaciations and frequent fires have provided nutrient-poor conditions and some of the least productive seas on earth



• annual variations in rainfall greater than within-year seasonal variations (El Niño – Southern Oscillation); ca 1/3 of all bird species nomadic, and large proportion nest in tree hollows (ca 11% are obligate cavity nesters; about twice as many as on any other continent)

• 1592 landbird species; 2nd richest in landbird species per unit area; high speciation due to fragmented nature of forests and many islands; 25% of families, 61% of genera and 89% of species endemic; 2nd highest degree of endemism (after Neotropics)

• avifaunal differences between Guinea, Australia and Tasmania are mainly related to habitat difference



• parrots, pigeons and doves, kingfishers and honeyeaters very well represented (latter most diverse group in Australia and New Guinea)



• curious birds are Birds-of-Paradise, Bowerbirds, Megapodes, Kiwis, etc.



• based on fossils, major components inherited directly from Gondwanaland (earliest know passerine early Eocene, ca 55 mil y ago); autochthonous component also includes Ratites, Penguins and possibly Lyrebirds, Pigeons, Parrots, Kingfishers

• relatives (same families) in Africa and South America reflect a common origin; some families currently restricted to region are represented among Eocene/Oligocene fossils from Eurasia (Owlet-nightjars, Frogmouths, etc)



• DNA-DNA hybridization indicates that passerines mainly result from endemic radiation within Australia rather than from successive colonization from Eurasia; majority fall into 3 distinct assemblages with convergence in form and habit towards unrelated birds in northern hemisphere



Relationships and divergence of Australian passerines



• 2nd major component from Palearctic-Oriental regions where close relatives are now found, followed by secondary radiations (e.g. Waterbirds, Raptors, Swifts, Pittas, Swallows, Thrushes, Silver-eyes); show varying degrees of differentiation (including distinct genera)


Decline in species numbers and diversity between Afrotropical-Indomalayan regions and Australasia




• very few characteristic Australian genera breached Wallace’s line to reach the oriental Region, and none reached Africa; unequal exchange between continents may reflect competitive superiority of members of one avifauna



• New Guinea is tropical, mountainous and wet, close to the Oriental Region and has rich avifauna (i.e. more species than Australia); centre of distribution of Birds-of-Paradise, Bowerbirds, Cassowaries, Megapodes and Crowned pigeons

• New Caledonia separated from Gondwana about the same time as New Zealand, and has a poor avifauna (71 species), including the flightless Kagu (separate family), 4 other endemic genera and 14 endemic species



• avifauna of New Zealand has 3 components: ancient group, Australian colonists, and Holarctic colonists

• new Zealand wrens and extinct Moa preceded split with Australia; other ancient species (without close relatives elsewhere) comprise Wattlebirds (e.g. Saddleback), Kokato and the extinct Huia and New Zealand thrushes

• insular influences are seen in flightlessness, lack of sexual dimorphism, and melanistic forms (common cause: lack of selection pressure in absence of mammalian predators)

• 2nd component (Australian origin) includes Dollarbirds, Parrots,…



• in recent times, habitat shifts due to anthropogenic activity increased chances of vagrant establishment (at least 8 Australian species during last 150 y)

• 3rd component (Holarctic origin) includes species such as South Island (Pied) Oystercatcher and New Zealand Scaup



• like Madagascar, New Zealand has very low species-per-genus ratio suggesting recent extinctions and little recent speciation

• mt DNA in museum specimens suggest major genetic bottleneck ca 28 mil y ago (Oligocene) and radiation from one/few mitochondrial lineages within each group

• New Zealand experienced very different history from rest of Australia (colder, frequent glaciations and volcanic activity, resulting in more fertile soils)


Nearctic regionNearctic region



• North America N of the tropics and Greenland; S border usually placed through Mexico, along N edge of the tropical rain forest (climate-vegetation boundary)

• covers ca 21 mil km² landmass and 2 mil km² ice (Greenland)

• in contrast to Europe, major topographical features extend longitudinally; hence areas E/W of Rockies have large numbers of exclusive species despite similar habitats; smaller areas of endemicity on mountain/lowland areas



• also latitudinal change in avifauna, with climatic and vegetation belts increasingly better defined northwards

• 732 regular breeding species, less than in any other region; no endemic bird families, but 19% genera and 54% species endemic



• North American continent connected with Europe (via Greenland) in early tertiary and intermittent connections with Asia across Bering Strait bridge (only 10.000 y ago); connection with South America occurred ca 3.5 mil y ago (Pliocene)

• as Central America is well vegetated, much less separation of Nearctic-Neotropical avifaunas than of Palaearctic-Afrotropical

• S half of North America was humid and tropical as far N as San Francisco/Washington DC during 1st half of Tertiary, permitting evolution of tropical North American fauna (distinct of South America); intermingled when Panamanian land-bridge established



• avifauna consists of 4 elements: (i) old indigenous (Wrens, Dippers, Gnatcatchers, Silky flycatchers, American sparrows, Motmots), (ii) young Holarctic (trans-atlantic connection with Europe but origin uncertain: Cranes, Grouses, Thrushes; (iii) recent immigration from Asia (Horned lark, Brown creeper, Pipits, Nuthatches, Corvids, Tits, Kinglets, Barn Owl, Hirundines); (iv) immigrants from South America with major radiation in North America (Tyrannid flycatchers)



• Greenland mostly considered part of Nearctic Region; among 59 regular breeders, 38 circumpolar, 8 from Europe, 13 from Eurasia

• as almost whole of Greenland was ice-covered until 6.000 years ago, much of its avifauna results from recent immigration; yet, its Redpolls are considered subspecifically endemic


Neotropical regionNeotropical region



• includes Central and South America, West Indies and other islands near South America (incl. Galapagos and Falklands); ca 18.2 mil km²

• mainly covers tropical forest, but also desert, grassland (pampas) and temperate/montane habitat



• a few tropical species (Trogon, Chachalaca) extend into North America, while some Nearctic species such (e.g. Turkeys) extend into South America

• Central America contains mix of old indigenous species and recent invadors from South America (Tinamous, Jacamars, Puffbirds, Toucans, Ovenbirds, Antbirds, Manakins, Cotingas)

• northward spread of open-country species due to destruction of former forest barriers



• contains longest mountain range (Andes) with central high desert (Altiplano) holding largest expanse of salt; Amazon (> 5000 km) drains 40% of continent and acts as significant dispersal barrier; largest seasonal swamp (Pantanal, > 60.000 km²), true desert (Atacama)

• richest in breeding bird diversity (3370 breeding species, 2 endemic orders, 20 endemic families, 686 endemic genera, 3121 endemic species); shares 7% species but 65% families with nearctic Region

• highest level of endemism reflects ancient and distinctive evolutionary history

• many migrant species from North America, mainly wintering in forest



• South America was isolated as a giant island continent for more than 30 million years



• characteristic families (Guans, Ovenbirds, Woodcreepers, Ground antbirds, Tyrant flycatchers, Cotingas, Manakins, Puffbirds, Gnatcatchers, Jacamars, Motmots, Barbets, Toucans, Tapaculos, Tinamous) underwent extensive evolutionary radiation during Pliocene and Pleistocene (1137 species, i.e. > 10% of all species)



• some endemic species could be relicts from former widespread distributions

• also many endemic fresh/saltwater birds (Torrent duck, Coscoroba swan, Steamer duck); however Cranes, Bustards, Hornbills, Corvids, Titmice, Nuthatches, Treecreepers and Shrikes largely absent



• diversity due to (i) extent of rain forest, (ii) N- and S-American fauna mixing at end Pliocene, (iii) high regional endemism, (iv) fewer Pleistocene extinctions due to less drastic glaciations, (v) speciation due to long isolation, (vi) pronounced altitudinal zonations, (vii) recent human colonization

• contains ca 90% of all suboscine birds, while dominant oscines (> 4000 species worldwide) proportionally least abundant

• ‘Great American Interchange’: more species colonized from N to S than vice versa (Tanagers, Cardinals, Thrushes, Pipits, Horned lark, Short-eared owl)

• flightless ratites of Africa, South America and Australia probably remnants of former Gondwana



• South America and Africa share various families (Trogons, Parrots, Jacanas, Painted snipes, etc) but only 17 species; possibly as a result of ocean crossing via stepping stones (ancient volcanos in south Atlantic)



• West Indies (Greater and Lesser Antilles, Hispaniola, Carribean) have impoverished avifauna (280 breeding species, 31 endemic genera, 150 endemic species) received by dispersal; level of endemism surprisingly high given proximity of both North and South America



• Galapagos, Falklands and Juan Fernandez archipelago received most of their fauna from adjacent parts of South America


OceaniaOceania


OceaniaOceania

• Pacific Ocean occupies > 1/3 of earth’s surface (> 166 mil km²); more than 23.000 small (tropical and subtropical) islands, mostly volcanic, mainly in C and SW parts of ocean

• divided into 3 regions: Micronesia and Melanesia (west) and Polynesia (central); islands only cover 46.632 km² (> 50% contributed by three islands; e.g. Hawaii); some coral atolls (Tuomota archipelago) below 7m altitude

• avifauna derived by cross-water colonization; hence small number of taxa and strong affinities with nearest continent; largest families are Whistlers, Doves, Flycatchers, Rails, Parrots and Honeycreepers


OceaniaOceania


OceaniaOceania

• islands fall into 5 biogeographical regions, but central Pacific ones usually treated as Oceania; 187 landbirds in 23 families; represents 20 x species density of richest continent; 38% genera and 87% species endemic

• striking examples of recent species formation and faunal attenuation, i.e. successive families, genera and species dropping out with increasing distance from continental source


OceaniaOceania

• Hawaiian archipelago more than 4000 km off north America, yet still containing most diverse island fauna; half of avian colonizers from North America; many species extinct following human colonization


OceaniaOceania

• avifauna of Oceania most severely impacted


AntarcticaAntarctica


AntarcticaAntarctica

• comprises main continent of Antarctica and all islands, sea ice and ocean northwards to Antarctic Convergence

• remaining fragment of ancient Gondwana which drifted to present position over south pole; colder than arctic

• 14.3 mil km² covered with thick glacial ice which is unsuitable for birds; at the end of summer, sea freezes from shoreline outwards (ca 3 km/day; doubling size continent by end of winter)

• no landbirds on main land-mass, seabirds dominated by Penguins and Petrels; sub-antarctic islands (South Georgia, Kerguelen, Macquarie) hold 4 Ducks, 1 Pipit, Common starling and Lesser redpoll (both self-introduced from New Zealand) and introduced Rail

• Shearwaters, Gadfly petrels and endemic landbirds north on temperate sub-antarctic islands (Tristan da Cunha, Chatam)

ConclusionsConclusions

Species numbers and diversitySpecies numbers and diversity

• overall, about 91% of landbird species are only found in a single biogeographical region

• moving through taxonomic hierarchy, distributions change progressively from restricted to widespread; only 4 out of 23 landbird orders are represented in a single biogeographical region

• differences can be attributed to greater age of higher taxa and greater opportunities through time for wider dispersal

• regions differ in numbers and densities of breeding birds and of species per family, due to (i) different past events of autochthony, colonization and in situ speciation (versus extinction), (ii) K-values to support large numbers of different taxa; (iii) past extent of glaciation; (iv) human impact

Species numbers and diversitySpecies numbers and diversity

• # species/mil km²: (S) Neotropical (3370/185) > Australasian (1592/179) > Afrotropical (1950/93); (N) Oriental (1697/177) > Neartic (732/35) > Palaearctic (937/20)

• at higher taxonomic levels, differences between regions are less marked, with Afrotropical region emerging as richest (breeding species of 54% families and 83% orders)

• Neotropical region holds extremely high number of species per family (average 47.5, Tyrannidae 544 species) and proportion of endemic species and families; also has the most distinctive bird fauna, followed by the Afrotropical, Australasian, Indomalayan, Nearctic and Palaearctic

• each region has own dominant groups (large numbers of species, large morphological and ecological diversity): North America (Parulid warblers), South America (Tyrannid flycatchers), Eurasia (Silviid warblers), Africa (Weaver finches), Australia (Honeyeaters)



Percentage of landbird orders, families and species that breed in 1-7 biogeographical regions

Meeting of faunasMeeting of faunas

• continental interchange is more marked in New than Old World due to the absence of massive east-west barriers (mountain, sea, desert) isolating temperate from tropical avifaunas

• Tyrannidae, Vireonidae and Parulini are probably of tropical origin whereas equivalent insectivores (Sylviidae, Muscicapidae, Turdidae and Oriolini) are probably of Palaearctic origin

• faunal exchange is predominantly unidirectional, depending on relative number of species in each land area and relative competitiveness (i.e. disproportionale colonization of South America by North American mammals)


Meeting of faunasMeeting of faunas

• distinctiveness biotas probably maintained by resistance to invasion (e.g. by competition): if resident species exploit all ecological opportunities, new species may have difficulties to establish (especially when adapted to different faunal backgrounds)

• alternatively, local adaptation may be more important than competition

• introduced species mainly restricted to man-made habitats, rarely penetrating remaining natural habitats which continue to hold native birds

• based on fossil records, (i) bird distributions have changed greatly since the start of the Tertiary (ca 65 mil y ago) and (ii) many endemic families once occurred in other regions as well


Island birdsIsland birds

• around 1627 landbird species occur only on island (ca 17% of all non-marine species)

• combined for all islands, overall species density nearly 4 times greater than averaged for continents

• islands are also important for nesting seabirds (not included above)

• percentage birds on islands is much higher than in other types of animals due to their superior dispersal powers

• tropical Pacific islands of Oceania collectively hold greatest density of bird species (187 endemic landbird species)

• study of island birds have had major influence on evolutionary and biogeographical theory; behave like ‘replicated experiments’



Island types classified according to mode of origin


Relationships between species number, island size and level of isolation

Decline in occurrence of (sub)families of breeding landbirds from New Guinea eastwards on various Pacific Islands



Sequence of island colonisation from a mainland source

SeabirdsSeabirds

• seabirds generally do not follow same biogeographical patterns as landbird species

• include ca 320 species (skuas, skimmers, gulls, terns, auks, tropicbirds, boobies, gannets, shags, cormorants, frigatebirds, penguins, loons, petrels, shearwaters, albatrosses); 5 of 8 groups entirely marine; distinction with landbirds not always clearcut

SeabirdsSeabirds

Seabird species following classification by Sibley & Monroe 1990

SeabirdsSeabirds

• form only 3% of world’s bird species, despite fact that sea water covers >66% of surface; however, collective biomass probably outweighs landbirds

• dependence on land varies between species; distribution mainly governed by latitudinal marine zones, distribution of food within those zones, and location of nesting places

SeabirdsSeabirds

SeabirdsSeabirds

Latitudinal biogeographical sea water zones

• Procellariiformes (petrels) are most pelagic of all seabirds

SeabirdsSeabirds

• capacity to exploit distant food-supplies being helped by:

(1) lower body T (38°C) and thus lower energy demands

(2) ability to lay down subdermal fat and stomach oil

(3) dynamic flight mode which additionally conserves energy

(4) ability to feed by day and night (excellent olfactory sense)

(5) ability of eggs to resist chilling and chicks to become torpid

SeabirdsSeabirds

• very few seabirds species compared to landbirds; 3.3% species on 71% Earth surface

• sea is one of the least productive ecosystems per unit of surface area (only 0.25% of primary production)

• all seabirds are carnivores (among vertebrates, species richness of carnivores only 10% of herbivores)

• most seabirds are confined to relatively shallow coastal areas, and all species are tied to land for breeding

SeabirdsSeabirds

• throughout the evolutionary history of birds, sea areas have remained interconnected; coastlines of all main continents either connected or within flying distance of neighbouring continents

• extreme mobility of most seabird species

• life at sea constraints body designs, colours and sizes of a birds to a more narrow range of options

SeabirdsSeabirds

• seabirds may have resisted extinction partly because of:

(1) their large geographical ranges

(2) their widely separated, largely inaccessible nesting sites

(3) the fact that younger age classes of many species tend to remain at sea away from vulnerable nesting colonies (e.g. Short-tailed albatross)

SeabirdsSeabirds

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