Sea-Birds. James Fisher

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      FIG. 3

      Diagrammatic family tree of sea-birds, mainly after Hildegarde Howard (1950)

      According to Howard (1950) a few living species of birds have been recorded from the Upper Pliocene, but large numbers of modern forms occurred in the Pleistocene. Of course in the Pleistocene the oceans approximated very closely to what they are today, with the Central American land-bridge closed, the Norwegian Sea wide open between Arctic and Atlantic Oceans, the Mediterranean a blind diverticulum of the North Atlantic. We need this picture as a background to a consideration of the North Atlantic’s present sea-bird fauna, for we shall find that it has few sea-bird species of its own, and only two genera; for the primary sea-bird species which now breed in the Atlantic (and Mediterranean) and in the neighbouring parts of the Arctic, and nowhere else in the world, are no more than twelve: the Manx shearwater Puffinus puffinus^*; the very rare diablotin and cahow of the West Indies and Bermuda (Pterodroma hasitata and P. cahow); the storm-petrel Hydrobates pelagicus; the North Atlantic gannet Sula bassana; the shag Phalacrocorax aristotelis; the lesser black-back Larus fuscus; the great blackback L. marinus; the Mediterranean gulls L. melanocephalus and L. audouinii; the Sandwich tern Thalasseus sandvicensis; the razorbill Alca torda, the puffin Fratercula arctica; besides the extinct Alca impennis, the great auk. The two present genera peculiar to the North-Atlantic-Arctic are Hydrobates and Alca.

      The sea-birds which qualify by birth and residence to be members of the North Atlantic fauna (excluding purely Arctic and Mediterranean species) include thirteen tubenoses, seventeen cormorant-pelicans, fourteen gulls, nineteen terns, two skimmers, four skuas and five auks (besides various secondary sea-birds, notably about eighteen ducks, three divers and two phalaropes). If we are to understand how these have got into the North Atlantic we should analyse the present distribution of the sea-bird orders and groups as between the different oceans.

      The most primitive group of sea-birds, yet the most specialized, is that of the penguins. The Sphenisci have fifteen species in all, of which eight breed in the South Pacific, seven in the Antarctic Ocean, five in the South Atlantic and two in the Indian Ocean. One (and one only) reaches the Equator, and thus the North Pacific, at the Galapagos Islands. No live wild penguin has ever been seen in the North Atlantic.^* It seems certain that the evolution of this order of birds has taken place in Antarctica and in the neighbouring sectors of the South Pacific.

      The great order of Tubinares the albatrosses, petrels and shearwaters, probably originated in what is now the South Pacific. Nobody knows exactly how many species belong to this order, as there is a good deal of disorder in the published systematics of this very difficult group; but the number is certainly eighty-six, and may be over ninety. Of these fifty-four breed in the South Pacific, twenty-seven in the Antarctic, twenty-five in the North Pacific, twenty-four in the South Atlantic, seventeen in the Indian Ocean, thirteen in the North Atlantic, three in the Mediterranean, and only one, the fulmar, in the Arctic Ocean.

      The Steganopodes are an order which is particularly well represented in the South Pacific and Indian Oceans. The pelicans, gannets, cormorants, darter, tropic– and frigate-birds number fifty-four species in all. Thirty-one breed in the South Pacific. Twenty-eight breed in the Indian Ocean. The North Pacific has twenty-three, the South Atlantic twenty, the North Atlantic sixteen, the Mediterranean six, the Antarctic three, and the Arctic two. The present distribution suggests that the order radiated from what is now the East Indian region—from south-east Asia or Australasia.

      In the order Laro-Limicolae the family Chionididae, two curious pigeon-like sheathbills, Chionis, are found in Antarctica; and one also breeds in the South Atlantic and South Pacific.

      In the family Laridae the gulls (subfamily Larinae) number forty-two. In the North Pacific sixteen of these breed, in the North Atlantic fourteen, in the Arctic eleven, in the South Pacific nine, in the Indian Ocean six, in the South Atlantic five, in the Mediterranean five, in the Antarctic two. Besides these two breed inland only in North America, one inland only in South America, and three inland only in the Palearctic Region. This appears to be the only group of sea-birds whose evolutionary radiation may have taken place from the north; the Arctic and neighbouring parts of the North Pacific and Atlantic appears to be the origin of the gulls. The terns (subfamily Sterninae) number thirty-nine, of which twenty-three breed in the North and twenty-two in the South Pacific, nineteen in the Indian Ocean, nineteen in the North Atlantic, fifteen in the South Atlantic, ten in the Mediterranean, two in the Antarctic, two in the Arctic and one inland only in South America. The radiation of terns appears to be pretty general over the world’s seas, and they may have originated in the tropics, perhaps in the Indian Region. The skuas (subfamily Stercorariinae) have only four species, one of which (Catharacta skua, the great skua) has its breeding-headquarters in the Antarctic; it also breeds in the South Pacific, South and North Atlantic. The other skuas have an arctic breeding-distribution which extends into the North Pacific and North Atlantic. The three skimmers Rynchops belong to a separate family, Rynchopidae; North Atlantic, South Atlantic and South Pacific each have two; the Indian Ocean has one. Some workers regard them as all of one species.

      The family Alcidae (the auks) take the place in the north of the penguins of the south. Undoubtedly their origin has been in or not far from the Bering Sea. Of the twenty-two species, sixteen belong to the northern part of the North Pacific, twelve to the Arctic Ocean north of the Circle, and six to the northern part of the North Atlantic.

      This concludes the list of sea-birds belonging to groups of super-family or higher status whose evolution has been marine. There are several further (secondarily marine) groups which contain sea-birds, or part-time sea-birds; thus all four members of the order Gaviae the divers, breed in the Arctic, and North Atlantic and Pacific regions, and winter at sea on the coasts of the oceans. Many of the twenty species of grebes, order Podicipedes, are marine outside the breeding-season, and six of them visit the coasts of the North Atlantic at that time. Among the geese and ducks many (see Appendix, see here) are partly marine, and some (e.g. eiders and scoters) are largely marine in the breeding—as well as in the off-season: two eiders and three scoters breed in the North Atlantic-Arctic. Among the waders (Charadriidae) the subfamily Phalaropinae contains only three members, all of which breed in the Arctic, North Atlantic and North Pacific, and two of which winter in the open sea.

      If we ignore these secondary sea-birds, and consider the 267 species of the primary marine groups, we find that the hierarchy is this: South Pacific 128 (51 per cent.); North Pacific 107 (40 per cent.); North Atlantic 74 (28 per cent.); South Atlantic 73 (27 per cent.); Indian Ocean 73 (27 per cent.); Antarctic 44 (16½ per cent.); Arctic 31 (11½ per cent.); Mediterranean 24 (9 per cent.); and purely inland only 7 (2½ per cent.).

      It can be seen that the North Atlantic, with its seventy-four species, is much lower than either half of the Pacific than would appear warranted by its area. There is not the faintest hint, from the radiation of any of the sea-bird groups, that either North or South Atlantic has been the arena of any great evolutionary changes. The Atlantic has been colonised from without; by penguins from the Antarctic; by petrels from the South Pacific; by pelecaniform birds and terns probably from the Indian Ocean; by gulls and auks from the Arctic. The North Atlantic and the immediately neighbouring parts of СКАЧАТЬ