(5)

FIELD NOTES ON THE NESTING HABITS OF THE GREAT NORTHERN DIVER.

BY

G. K. YEATES.

(Plates 1—9).

THE following notes on the Great Northern Diver (Colymbus immer) were made chiefly at a nest on the great lake of Thingvallavatn in South-west Iceland during June, 1949. They are supplemented by field notes made during the previous June in the hill-lake country east of Stathur on the Hrutafjord (North Iceland). In 1948 I was accompanied by Captain T. B. W. Jeans, and in 1949 by Dr. K. J. Carlson.

The present status of the Great Northern Diver in Iceland is most satisfactory, for wherever there are many hill-lakes, it may be confidently expected in numbers, comparable at least with those of the Black-throated Diver (C. arcticus) in the Western and North­western Highlands of Scotland. Of this healthy state we had plenty of evidence at Stathur in 1948, when in the evening, during the " night " and at dawn the high-pitched, almost idiotic-sounding,-flight-calls of birds coming and going from their fishing in the fjord were constantly in our ears, and made us realize that in the great inland sea of lakes which stretched away to the east a very consider­able number of pairs must have been nesting. In point of fact, in the area immediately behind our camp which we worked intensively we knew of three nesting pairs, but that area was but a tiny portion of the whole suitable terrain. In the south-west the bird is not, and never has been, so common, but it appears to occur wherever it can find a large enough lake of reasonable privacy. It is indeed good to be able to state that at least two pairs still nest on Thing­vallavatn, as Jourdain (1) recorded over 30 years ago. And Thing­vallavatn can by no stretch of the imagination be regarded as remote. It is indeed after early June the popular boating, fishing and camping resort of Reykjavik. Dr. Finnur Gudmundsson also informs me that of recent years this species, and with it the Whooper Swan (Cygnus cygnus), has steadily colonized lakes ever further into the interior of Iceland and ever further from the sea. Of other parts of the country there is no reliable information since before the war, but there is little cause to doubt that the healthy position described by Vesey (2) for the north-west and Morrison (3) for the north-east is to-day being maintained. There is indeed little reason for it to be otherwise, for apart from the occasional loss of eggs to a Great Black-backed Gull (Lams marinus) and doubtless at times to other predators, and the even more unusual fate of an odd adult being caught in a fishing-net, of both of which I have had experience, the " Himbrimi " is a bird beloved by the Icelandic farmer, and none would lay destructive hands on him. Add the remoteness of many of its nesting lakes and Selous's (4) lugubrious, but rather previous,

6 BRITISH BIRDS. [VOL. XLIII.

lamentations at the coming extinction of the species in Iceland hardly make sense.

In its choice of breeding haunt the Loon approximates closely to the Black-throated Diver. It avoids small lakes, and appears to nest only on waters of considerable acreage, unlike its extremely abundant neighbour, the Red-throated Diver (C. stellatus), which seems happier on a small bog pool. It also, like the Black-throat, prefers the security of an island, but apparently it will not hesitate to nest on the mainland shore of a lake, though we never saw on either visit such a site. I could find no evidence that in Iceland the bird ever constructs the bulky, and often floating, reed nest so commonly reported from the New World (Bent (5) ; Dunlop (6)).

The breeding-season varies with the earliness or tardiness of spring. In the open year of 1948 Jeans and I saw swimming chicks, perhaps 72 hours old, on June 18th. These eggs must therefore have been laid at least by mid-May. In the very late season of 1949, when the lakes of North Iceland were still ice-bound in mid-June, Carlson and I found a hardy pair on Thingvallavatn which had a clutch of two eggs on June 2nd. From the fresh state of the grasses in the nesting-scrape, and above all the fact that no brown " earth-patches " had been worn by the eggs, we judged that the incubation had only just begun, a few days at most before that date.

Male and female are closely linked throughout the nesting cycle, though the female certainly bears the brunt of the incubation. The male, however, is rarely far away, and when the nest is approached by any possible danger, he appears, often " from nowhere," cruising up to the home waters in support of his mate. She, leaving the nest, immediately joins him, and the two birds ride close off-shore together, and are, as Dunlop (6) also describes, extraordinarily fearless. When the danger passes, both birds return to the vicinity of the nest, one departing " out to sea " as soon as the nest is again occupied by its partner. With chicks the link is even closer, and Jeans and I saw one chick on the back of each parent.

We were too late to see anything of courtship, but three " dis­plays " were observed. Neck-outstretching and wing-arching, typical diver postures, were frequent and appear to serve as a normal greeting. So too were bill-dipping and the rolling-preen, in which, with one leg paddling and the white underparts revealed, the bird rotates around one spot. More unusual, but apparently the same as that noted by Dunlop (6) and Forbush (quoted in Witherby (7)), was the occasional display of the male in which a curious upright position was assumed. Rearing up until he appeared to be sitting on his tail, he thrashed the surface with his paddles, but with closed wings, and rushed over the lake, making the water fly and creating a considerable commotion. In this attitude, erect and upright, white belly to the front, the bird bore a remarkable resem­blance to a penguin. This imposing display was apparently incited, though not by any means at every visit, by our appearance on the

VOL. XLIII.] NESTING OF GREAT NORTHERN DIVER. 7

nesting islet. Once, however, it appeared to be evoked by the presence of a third Loon near the nest. We interpreted it as a threat display.

A third ceremony was a prolonged flight, with an introductory dance-game and a wild chorus. On occasions, when the birds were disturbed, they did not return directly to the nest when the coast was again clear, but, drifting out into the lake, made the welkin ring with a quite indescribable chorus of fiendish and blood-curdling yel­ling, a noise which puts into the shade even the unearthly shrieks and howls of the Black- and Red-throated Divers. While this satanic overture was being played, the birds would swim low in mock pursuit of one another, but towards the end they would draw into position for the " take-off"—dead level like horses on the tape. The " singing " ceased, they taxied in silence and, as they became air­borne, they once again shouted at the top of their voices, but now much of the devilry is out of the song, and it is a long-protracted wailing which can be heard at a very great distance. This they continue to make as long as they are in the air together. This may be for quite a time, for they frequently did a round-trip over the huge nesting lake which could hardly have been less than ten miles. All the while they fly dead level. Nearing the home waters, they cease to call, and arching their wings, swing in neck and neck, to cut in alighting a great furrow of water, like great Sunderland flying boats—a most thrilling performance to observe.

These cacophonous duets of the Great Northern Diver defy description in words. I agree with Bent (5), that he is a wise man who does not try to set such music to syllables.

It is perhaps a measure of the difficulty of doing so that although I spent three weeks in the almost constant company of these birds during 1948 and 1949, and became very familiar with their wide vocabulary, I even so find it very difficult to be sure to which of the notes I recognized are to be referred the various calls which are carefully distinguished and separated by W. L. Underwood (in Bent (5)).

Perhaps the most characteristic note of the Loon, however, is easily and accurately set in syllables—a loud, far-carrying, high-pitched hoo - hoo - hoo. This is, in my experience, essentially a flight-call, and it is this call to which the birds give incessant tongue when moving between nesting lake and feeding lake or fjord. The kwuck - kwuck call of The Handbook is one which I cannot recognize and which does not seem to appear in any shape in my notes or memory. I have, however, heard the hoo - hoo note from a sitting bird which used it in staccato bursts of excitement at the sight of her mate and two other Loons assembled on the water within 200 yards of her nest. The occasion, indeed, was altogether too much for her, for she joined the party at speed, still hoo - hoo - hoo - ing, in greeting or anger, whereat there was much splashing of water, and much dash­ing over water in that extraordinary " game " of diver-chase-diver,

8 BRITISH BIRDS. [VOL. XLIII.

necks outstretched, bodies half-submerged, while a chorus from all the devils in hell rings to the hills. In that wild setting of snow-clad mountains I know of no bird-scene in my experience more romantic or more inspiring, nor do I ever wish to see—or hear—a grander.

REFERENCES. (i) JOURDAIN, F. C. R. (1913). " Notes on the Birds of South-West

Iceland." British Birds, Vol. vi, pp. 235-45. (2) VESEY, A. H. (pseud. Lewis, Ernest) (1938). In Search of the Gyr-

Falcon, p. 232. (3) MORRISON, A. (1938). " Notes on the Birds of North-East Iceland."

Ibis, 1938, pp. 129-36. (4) SELOUS, E. (1913). " A Diary of Ornithological Observations made in

Iceland during June and July, 1912." Zoologist, 1913, pp. 409-422. (5) BENT, A. C. (1919). " Life Histories of North American Diving Birds."

Bull. No. 107, U.S. Nat. Mus., pp. 47-60. (6) DUNLOP, E. B. (1915). " Notes on the Great Northern Diver." British

Birds, Vol. ix, pp. 142-147. (7) WITHERBY, H. F., et al. (1940). The Handbook of British Birds,

Vol. iv, pp. 121-116.

British Birds, Vol. xliii, PI. 1

UPPER.—THINGVALLAVATN, S.W. ICELAND, FROM THE TOP OF THE ALMANNAGJÄ : BREEDING HAUNT O F T H E GREAT NORTHERN DIVER (Colymbus

immer). LOWER.—THINGVALLAVATN : NESTING ISLET OF GREAT NORTHERN DIVER

(Colymbus immer). (Photographed byG. K. Yeates).

GREAT NORTHERN DIVER (Colymbus immer). MALE ON NEST : NOTE HEAVIER HEAD AND STOUTER BILL THAN FEMALE.

(Photographed by Dr. K. J. Carlson).

British Birds, Vol. xliii, PI. 2.

British Birds, Vol. xliii, PI. 3.

G R E A T N O R T H E R N D I V E R (Colymbus immer). F E M A L E O N N B S T : N O T E S M A L L E S H E A D A N D S L I G H T E R B I L L T H A N M A L E .

(Photographed by G. K . Y e a t e s ) .

British Birds, Vol. xliii, PI. 4

G R E A T N O B T H E R N D I V E R (Colymbus immer). ' A L A R M ' POSITION ON N E S T .

(Photographed by G. K. Yeates) .

British Birds, Vol. xliii, PI. 5

G R E A T N O R T H E R N D I V E R (Colymbus immer). T U R N I N G EGGS : B A C K V I E W .

(Pholographed by G. K. Y e a t e s ) .

British Birds, Vol. xliii, PL 6.

G R E A T N O R T H E R N D I V E R (Colymbus immer). T Ü R N I N G KGGS.

(Photographed by B jö rn Björnsson) .

British Birds, Vol. xliii, PI. 7.

G R E A T N O R T H E R N D I V E R [Colymbus immer). O N NEST.

(Photographed by B jö rn Biörnsson) .

British Birds, Vol. xliii, PI. 8.

G E E A I N O R T H E R N D I V E R (Colymbus immer). O N W A T E R NEAR NEST. (Photographed by Björn Björnsson) .

British Birds, Vol. xlii, PI. 9.

GREAT NORTHERN DIVER (Colymbus immer).

U P P E R . — N E S T AND EGGS.

(Photographed by G. K. Yeates).

L O W E R . O N WATER NEAR NEST.

(Photographed by Björn Björnsson).