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- 100%
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All the four skuas appear to vary in plumage; the bonxie (great skua) particularly in the amount of rufous colour, especially among some of its southern forms; the three smaller skuas have a ‘normal’ pale phase of plumage with light breast and underparts, and yellowish or buff on the sides of their necks; and a ‘dark’ phase which is almost uniformly, or uniformly, dusky; and intermediates. The dark phase of the long-tailed skua is so rare that it has hardly ever been seen. Among the population of pomarine skuas, wherever they may breed, from five to twenty per cent. are dark; the distribution of dark birds is even, in the sense that there is no detectable gradient. Southern’s detailed analysis (1944) shows that no geographical area contains significantly more dark pomarine skuas than any other. Among the arctic skuas (Southern, 1943), however, the situation is quite different. In the southern parts of this bird’s breeding-range about three-quarters of the birds are dark; in the middle parts about half, in the Low Arctic less than half, and in the High Arctic a quarter or less. In north-east Greenland, indeed, the dark form is unknown. There are a few, rare, birds intermediate in colour between the pale and dark forms. This looks like a quivering balance between two ‘stable’ types. The proportion of the colour-forms in the British colonies is (Southern points out) subject to rather special considerations, since the colonies are generally small and scattered, and thus liable to random fluctuations—in fact between the limits of 50 and 86 per cent. dark. The mean probably lies at about 75 per cent.
Southern has attempted to correlate the distribution of the dark arctic skuas (Fig. 10) with temperature, relative humidity and various ecological factors. His material carries darkness with humidity over a considerable part of the bird’s total range; but the correlation breaks down in Norwegian Lapland—also, good meteorological figures are not available for all the arctic regions.
FIG. 10
Distribution of colour-phases of the arctic skua, Stercorarius parasiticus, from H. N. Southern (1943), showing isolines for percentage of the pale phase in the breeding population.
We found the same difficulty in correlating the distribution of the colour phases of the fulmar, Fulmarus glacialis, with climate and other environmental factors. In the Atlantic (though not the Pacific) part of the fulmar’s range the situation is in many ways the opposite of that among the arctic skuas; where the surface of the sea is above freezing (i.e. in the Low Arctic and rest of the range) the fulmars are nearly all light. The gradient runs from 0 per cent. dark in Britain to a hundred per cent. (probably) in the High Arctic of Spitsbergen and Franz Josef Land; in West Greenland (Low Arctic) the fulmars are very nearly all light. Finn Salomonsen suggested to Fisher (1952) a correlation between this distribution (Fig. 11) and surface water-temperature. Dark fulmars are only found in the areas where the water is nearly freezing, or freezing, in July, in which month the adults collect food for the chick fulmar. It is interesting to note that approximately the fifty-fifty situation in the distribution of colour-phases of the fulmar (as also of the bridling in the guillemot) is found at Bear Island, whose position is between Low and High Arctic. However, the Pacific fulmar appears to reverse the situation found in the Atlantic; the dark fulmars are found in the warmer parts of the Pacific fulmar’s range, and the light fulmars progressively towards the colder parts, though nowhere does this race of the fulmar breed in truly High Arctic waters.
FIG. 11
Breeding distribution of the fulmar, showing the approximate preponderance of dark birds in the populations, indicated by the dark parts of the circles (from Fisher, 1952)
The existence of these polymorphic forms of some birds constitutes a problem of the greatest interest, which travellers and amateur naturalists might well help to solve by collecting simple counts of the relative proportions of easily recognisable forms.
CHAPTER 3 SEA-BIRD NUMBERS AND MAN
EVERY BIRD has a history, which is a tale of adventure and fluctuating fortunes, of success, or of failure; for every bird, like every other animal, suffers change. In any study of the life of birds, and the place of birds in nature, an understanding of their numbers is fundamental.
Since most sea-birds are social animals, and nest in colonies in wild and beautiful places, their numbers can often be studied very closely, and with a great deal of enjoyment. So enthusiastic is the average amateur bird-watcher about visiting sea-bird stations, and ‘collecting’ islands, that it is safe to say that every important seabird colony on both coasts of the United States (not Alaska), and on those of the Faeroes, Britain, France, Belgium, Holland, Denmark, Germany, Finland, and Sweden is known to somebody who can distinguish its birds from each other; and most of those in Norway, Spain, Portugal, Iceland and St. Lawrence-Canada are known. The sea-bird stations of Greenland, thanks to a tradition of accurate observers from Giesecke to Bertelsen and Salomonsen, are better known than those of the Canadian Arctic, Newfoundland, the U.S.S.R., China, and perhaps even Japan. Those of the Antarctic and Subantarctic, and South America, are perhaps better known than those of the tropical Pacific. Probably a very adequate list of the sea-bird stations of the United States (excluding Alaska) or of north-west Europe could be compiled by some bibliophilic ornithologist with access to all the local as well as national bird and natural history journals of those countries. Such lists would be useful documents; they would have to be carefully dated, because of what history tells us of the fortunes of animals, and of change. Fisher has recently compiled a dated list of all the fulmar colonies of the world, and we have both, at different times, compiled lists of the world’s gannetries. It is surprising how certain it is possible to be of being complete, within reasonable limits. Thus after the publication of his Report on the 1938 survey of black-headed gull colonies P.A.D. Hollom (1940) had no colony known (or not known) to be occupied in 1938 to add or subtract from his list of 342 such colonies. When Fisher and Vevers (1943–44) organised a census of the North Atlantic gannet in 1939, only two small colonies of the twenty-three which then existed were overlooked in that year. When Fisher and Waterston (1941) reported on the fulmar colonies known to them in Britain in 1939 they believed that there were 208 separate stations at which the fulmars were breeding. Ten years later, after carrying on research and correspondence with the same intensity to discover the situation in 1944 and 1949 (during which ‘back information’ was also collected), Fisher discovered that he had overlooked only nineteen, all small (and some in very remote parts), and unimportant as far as the fulmar’s population, or the actual extent of its range, were concerned.
A census of the sea-birds of the North Atlantic is no longer a wild dream. A start has been made with certain obvious species, with limited distribution or small populations. The organisational problems are not insuperable; we have an ever-increasing body of highly competent bird-watchers available for, and keen on, the counting of nests: for a sea-bird census depends on the assessment of the number of occupied nests. Such a census has already been performed for several species on the coasts of Germany (Schulz, 1947), and, judging from the descriptions of the distribution of sea-birds in Sweden (Lundevall, unpublished), Denmark (Jespersen, 1946, and Løppenthin, 1946), the Netherlands (van Ijzendoorn, 1950) and Belgium (Verheyen, 1951), it need not be long before a census of the southern North Sea and Baltic could be complete. In Britain good surveys, if not censuses, exist for the sea-bird colonies of most counties in England, and there are records published in the present century concerning almost every bird-cliff in mainland Britain (though not every species on the cliff) and many in the Hebrides, Northern Isles and Ireland. Complete censuses, or careful estimates, have been made of many species of sea-birds in various countries with a North Atlantic-Arctic seaboard; of which a selection is:
SOME CENSUSES
of apparently occupied nests (i.e. an approximation to the apparent total breeding pairs) of North Atlantic sea-birds in some parts of their range (in a few cases, world census). Censuses of single colonies are not included unless these are of great importance.
Fulmar, c. 100,000 in Britain, including St. Kilda, in 1949 (and five-yearly estimates since eighteen-seventies; Fisher, 1952): c.350 in Norway in 1947 (P. Valeur, 1947): c. 200,000 in West Greenland (F. Salomonsen, 1950): c.200,000 on Bear I. in 1932 (Bertram and Lack, 1933): c.100,000 + at Cape Searle, Baffin I. in 1950 (V. C Wynne-Edwards, 1952).
North Atlantic (Cory’s) shearwater, c.20,000 on the Salvages, pertaining to Madeira, in 1939 (R. M. Lockley, 1952).
Great (Tristan great) shearwater, world population between 2 and 2½ million, all on Tristan da Cunha in 1949–50 (M. K. Rowan, 1952).
Cahow, world population all on Bermuda where 13 or 14 nests found and 1951 population “perhaps of the order of 100 adult birds, there may be fewer, but there are not likely to be more.” (Murphy and Mowbray, 1951).
Leach’s petrel, c.2,000 in Britain; this estimate contains a guess of 1,000 nests on St. Kilda in 1931 which is unreliable since not all the St. Kildan islands on which the species nests were visited (Atkinson and Ainslie, 1940): c.13,000 in Newfoundland in 1942–45 (Peters and Burleigh, 1951).
American white pelican, world population c.15,000 in 1932 (B. H. Thompson, 1932).
North Atlantic gannet, world population c.83,000 in 1939, of which c.70,000 in Iceland-Faeroes-Britain; in 1949 c.82,000 in Iceland-Faeroes-Britain (Fisher and Vevers, 1943–44, 1951). See here.
Double-crested cormorant, Population entire n.e. subspecies P. a. auritus, c.20,000 in ’twenties (H. F. Lewis, 1929); re-established on eastern seaboard U.S. c.1925 (E. H. Forbush, 1925, H. L. Mendall, 1936); c.900 in 1931 (Norton and Allen, 1931), over 10,000 in 1944 (A. O. Gross, 1944).
European cormorant, in Holland c.1,200 in 1926, c.2,600 in 1934, c.4,000 in 1937, 4,622 (peak) in 1940, 4,359 in 1941 (van Ijzendoorn, 1950); in Belgium 30 in 1950 (R. Verheyen, 1951); in North America 1,086 in 1940 (H. F. Lewis, 1941).
Great skua, just over 100 in the Faeroes in 1942, c.200 in 1946 (K. Williamson, 1945b, 1948, L. Ferdinand, 1947); c.1,000 in Great Britain (all Shetland and Orkney) around 1946 (R. Perry, 1948, Royal Society for the Protection of Birds watchers and other sources).
Ring-billed gull, c.1,750 in Gulf of St. Lawrence in 1940 (H. F. Lewis, 1941b.).
Common gull, c.500,000 in Denmark in 1939 (P. Géroudet, 1946); 20,221 in Germany in 1939 (Schulz, 1947); c.250 in Holland in 1949 (van Ijzendoorn, 1950); a few occasionally on the Belgian border (Verheyen, 1951); c.30 in England in 1941.
Herring-gull, c.27,500 in Holland in 1938 (van Ijzendoorn, 1950); 28,569 on North Sea coast of Germany in 1939 (Schulz, 1947); under 9,000 in Maine in c.1900, c.16,500 in 1921, c.25,000 in 1931 (Norton in Palmer, 1949).
Lesser blackback, 1 in Germany 1927–28, c.6 in 1938–47 (Schulz, 1947); colonised Holland since 1926, not more than 50 (van Ijzendoorn).
Great blackback, c.1,100 in England and Wales in 1930 (Harrisson and Hurrell, 1933); c.20 in Denmark in 1941 (F. Salomonsen, 1943); 16 on Bear Island in 1948 (Duffey and Sergeant, 1950); 3 in United States in 1928, at least 1,250 in 1944 (A. O. Gross, 1945).
Laughing gull, c.25 in Maine in 1860–70, 1, 2, 3 or 4 from c.1884 to c.1918, c.150 in 1931, 1936, c.250 in 1937–38, c.300 in 1940, c.50 in 1941, none since. (Palmer, 1949); in Western U.S. 2 in 1928 (Miller and van Rossem, 1929).
Black-headed gull, 35,000 in England and Wales in 1938 (P. A. D. Hollom, 1940, S. Marchant, 1952).
Little gull, 15 in Holland in 1942, 18 in 1943, 13 in 1944, 1 or 2 in 1945, c.8 in 1949 (van Ijzendoorn).
Kittiwake, 6,000 to 8,000 in England in late 1940’s (J. Fisher, from literature and notes); 11 in Denmark in 1941, 15 in 1942, 124 in 1946 (Salomonsen, 1941, Løppenthin, 1948); 1–3 in Germany in 1938–39 (R. Drost, 1939); 24,400 in Newfoundland in 1941–45 (Peters and Burleigh); probably c.10,000 in Gulf of St. Lawrence in 1940 (H. F. Lewis, 1941b and others).
Black tern, 8 in Britain in 1941, 5 in 1942 (R. Cooke, 1946); none in other recent years.
Whiskered tern, 8 in Holland in 1938, 9 in 1945 (invasions; van Ijzendoorn).
White-winged black tern, 1 in Belgium in 1937 (R. Verheyen, 1951).
Gull-billed tern, 1 in Holland in 1931, 1 in 1944, 2 in 1945, 3 in 1949 (van Ijzendoorn).
Caspian tern, 300 in Germany in 1819, 25 in 1874, none since 1918; 7 in California in 1922, 296 in 1930, 378 in 1943 (A. H. Miller, 1943); c.200 in Gulf of St. Lawrence in 1884 (M. A. Frazar, 1887), 30–55 between 1925 and 1940 (H. F. Lewis, 1941b.), 45 in 1945 (O. H. Hewitt, 1950).
Common tern, c.4,450 in Maine in 1931–36 (Palmer, 1949); c.15,000 in Cape Cod region of Massachusetts in 1930–44 (O. L. Austin, 1946) ; 15,000–16,000 in Germany in 1939 (Schulz); c.19,000 in ‘de Beer’ sanctuary, Hook of Holland, in 1939 (van Ijzendoorn); doubtful whether in any year in the present century more than 7000 in England and Wales, and likely that over half of these have been in Norfolk (J. Fisher from literature and notes).
Arctic tern, c.5,970 in Maine in 1931–36 (Palmer); c.4,700 in Germany in 1939 (Schulz); probably under 200 in Holland (van Ijzendoorn); doubtful whether in any year more than 3,000 in England and Wales, and likely that over half of these have been in the Farne Islands (J.F.).
Roseate tern, c.276 in Maine in 1931–36 (Palmer); 1 or 2 in Germany in most years since 1904 (Schulz); 2 in the south of France in 1951 (R. M. Lockley); over 1,000 in the British Isles in recent years, about a third of which are in Anglesey and about half of which are in Ireland (J.F.)
Sooty tern, in Pacific c.166,950 on Laysan Island (Dill & Bryan, 1912); in Indian Ocean over 25,000 in 1937 on Goelette, c.65,000 on Bird Island (Seychelles), c.5 million in 1931 and at least ¼ million in 1937 on Desnoeufs (D. Vesey-Fitzgerald, 1941); in U.S.A. (breeds Dry Tortugas only) c.7000 in 1903, 9,000 in 1907, 10,000 in 1908, 9,000 in 1917, 15,000 in 1935, 20,000 in 1936, 50,000 in 1937, 32,029 in 1938, 35,000 in 1939, c.50,000 in 1940, over 50,000 in 1941, 32,500 in 1942, 54,500 in 1945, 48,600 in 1946, 32,135 in 1947 (P. Bartsch, 1919; A. Sprunt, 1948).
Sandwich tern, c.40,000 in Holland in 1940 (van Ijzendoorn, 1950); this perhaps four-fifths of whole population of north-west Europe; other occupied countries, all with very fluctuating numbers, Sweden (200–300 nests in early ’forties), Germany (3,957 in 1940), Denmark (unknown number), the British Isles (fluctuating between two and five thousand nests, and about 3,500 in early ’forties, J. F. from literature and notes), and Danzig, Brittany and Portugal (a few each).
Noddy, in U.S.A. 200 in 1903, 2,000 in 1907, 700 in 1908, 2,000 in 1917; 1,500 in 1935, 2,000 in 1936, 1,000 in 1937, 206 in 1938, 125 in 1939, 90 in 1940, 500 in 1941, 225 in 1942, 375 in 1945, 275 in 1946, 125 in 1947 (as sooty tern).
Little auk, in Iceland, now breeds Grimsey only, where c.50 in 1820, 150–200 in 1903, c.20 birds in 1934, at least 19 birds in 1949 (see here.)
Razorbill, 12 in Germany in 1939 (Schulz), all on Heligoland; 318 in Denmark in 1939 (Salomonsen, 1943), all on Græsholm, where 60 pairs in 1944 (K. Paludan, 1947). Peters and Burleigh (1951) suggest that there may not be more than 450 in Newfoundland.
Common guillemot, c.25,000 pairs in Sweden in early nineteen-forties (F. Salomonsen, 1944), nearly all on Störa Karlsö, where only 10 in 1880, c.1,250 in 1918; in Denmark established Græsholm in 1928, c.60 in 1936, 100 in 1938, 122 in 1939, 127 in 1940, 208 in 1941, 158 in 1942 (Salomonsen, 1943, 1943b); c.200 in c.1946 (P. Jespersen, 1946); in Germany c.2,000 all on Heligoland (Schulz and ourselves). Peters and Burleigh (1951) suggest that there may not have been many more than 25,650 in 1941–45 in the whole of Newfoundland, but it seems clear that the total west Atlantic common guillemot population is at least 40,000, of which there are about 7,700 in Quebec Labrador (R. A. Johnson, 1940), c.10,000 on Anticosti Island (H. F. Lewis, 1941c.), and perhaps 500 on Bonaventure Island in Quebec and 700 on the Bird Rocks in the Magdalen Islands (A. C. Bent, 1919).
Brünnich’s guillemot, c.2 million in Greenland (Salomonsen, 1951).
Black guillemot, c.250 in Maine in 1948 (Palmer); 3 in England in 1940 (Cumberland; Blezard and others, 1943).
Atlantic puffin, world population 1952, not less than 7,612,500, of which 2,500,000 each Iceland, Faeroes; 2,000,000 Brit. Is. (J.F. thinks this an under-estimate); 62,500 France, Channel Is. (R.M.L., 1953).
Though this list includes some very small numbers of sea-birds breeding in some countries and lands desultorily, or at the very edge of their range, there have been some big censuses; and of five North Atlantic sea-birds, Tristan great shearwater, cahow, American white pelican, gannet and puffin, we have estimates of the world population.
We must again remind readers that the figures do not refer to birds (unless this is particularly pointed out); but to occupied nests or breeding ‘pairs.’
Not many of the censuses made so far are of the species with very large populations. Indeed, if we were to judge solely from completed censuses, we might come to the conclusion that the populations of sea-birds were not high. In fact, they are often extremely high. “The Fulmar Petrel lays but one egg,” wrote Darwin in The Origin of Species, “yet it is believed to be the most numerous bird in the world.” We now know (Fisher, 1952) that, while there may be over two million, there are under ten million fulmars in the world, and that, far from being the most numerous bird, the fulmar is less numerous than many sea-birds, and even some land-birds. One of us has already suggested (Fisher, 1940) that “the most abundant bird in the world is certainly a sea-bird, and probably Wilson’s petrel,” and nothing discovered in the last ten years has encouraged him to change that view. Nevertheless, many species of sea-birds are astonishingly abundant, and quite a number of North Atlantic species, if not vastly numerous in the Atlantic proper, certainly darken the sky round their arctic breeding-haunts just as Wilson’s petrels darken some antarctic skies. The miles of cliffs round Bear Island (especially at its south end) harbour millions (an unknown number of millions) of Brünnich’s and common guillemots. Some of the buttresses rise fourteen hundred feet sheer from the sea, and, as Bertram and Lack say, “have been described with justice as the finest bird-cliffs in the Northern Hemisphere.” However, those of St. Kilda are (in one place) also fourteen hundred feet high, and are more varied, with a better-known history. Those who have seen both may think St. Kilda finer, though Bear Island has more birds and is more magnificently sinister. It certainly has a higher sea-bird population than any comparable place in the North Atlantic-Arctic; though it seems to have competitors in the Pribilov, Aleutian and Kurile Islands and other parts of the North Pacific. But there are many great bird-stations besides Bear Island and St. Kilda, where the observer may behold a community of a million birds or more. On the basalt cliffs of the Faeroes, particularly north-west Streymoy, he may find this number. Perhaps nowhere in Iceland is there a cliff-site with a million birds, but there are many rocks with many thousands, from the Westmann Isles in the south to Grímsey in the north; from Latrabjarg in the west to Skruður and Papey in the east. Jan Mayen has at least a million sea-birds; and there may well be millions at more than several places in Spitsbergen; perhaps on the hills of Horn Sound, Cloven Cliff off the north-west, Magdalena Bay and Brandy Bay in North-east Land; almost certainly on the Vogel Hoek of Prince Charles Foreland, the great auk hill of Advent Bay, and the dolerite Alkrange of Hinlopen Strait. A pioneer ecologist and student of animal numbers (Elton in Longstaff, 1924) wrote of the Alkrange:—
“It is impossible to describe the multitudes of the Guillemots on the bird cliffs. The place was teeming with them: literally hundreds of thousands. The cliffs are made of columnar dolerite which weathers into pinnacles and which rise several hundred feet sheer out of the sea. On the numerous narrow ledges the birds were so crowded that there was room for no more. The rows of black and white birds rising in tiers up to near the top, and the ghostly noise of the combined twitter made by them, made it seem as if one was in a vast opera house, packed with crowds of people in white shirt-fronts and black tails, all whispering comments on each other and rustling their programmes.”
It seems clear that either the little auk or Brünnich’s guillemot is the most abundant bird of the north. It is hard to decide which; the little auk colonies are perhaps fewer, and certainly less obvious as dense loomeries, because the birds nest in crevices and not on flat open ledges. But the dark cloud of circling, twittering dovekies betrays their density, and we believe with Salomonsen that their actual numbers are greater. Nevertheless, some Brünnich’s guillemot loomeries are vast, and those at Bear Island, Jan Mayen and Spitsbergen are not the only ones that are stupendous. The largest loomery in the U.S.S.R. is probably that at Bezymiannaya Bay in Novaya Zemlya, where S. K. Krasovskii (1937) has estimated that about 1,600,000 Brünnich’s guillemots (birds, not pairs) nest. But Salomonsen (1944) has estimated that in 1936 over two million Brünnich’s guillemots (birds) bred at the rock Agparssuit (Cape Shackleton), north of Upernavik in West Greenland. This was about half the population of this species in Greenland. There are many other huge bird rocks in Davis Strait and Baffin’s Bay; in West Greenland several on Disko Island, in Umanaq Fjord (notably Sagdleq, which may have a million Brünnich’s) and in the Upernavik district (notably Qaerssorsuaq, or Sanderson’s Hope, where the guillemot cliff is at least three miles long and over three thousand feet high and has two hundred thousand Brünnich’s), and several in the Thule district in the far north-west, notably Saunders and Hakluyt Islands, and Cape York, which contains what is probably the largest little aukery in the world;* nobody has been able to guess how many millions nest there.