OCR Text |
Show 528 MR. H. S A U N D E R S O N LARIDJE [June 6, hemisphere; but inasmuch as the Alcidce proper are now generally admitted to be connected with the Larida on the one side, as the Larida are connected with the Limicola on the other, and as the Alcida are only known to inhabit the northern hemisphere, it would appear more probable that the Larida, or at least the Larina, had their origin there also. There are, however, some very remarkable points about the Gulls of the southern hemisphere, especially with relation to the Pacific, of which M . Milne-Edwards seems to be unaware, and upon which I should like to offer a few observations. Throughout the northern hemisphere, exclusive of the shores washed by the Pacific, the Gulls (with the exception of the three arctic genera Rissa, Pagophila, and Rhodostethia) fall into two well-marked groups-those in which the adults bear a coloured hood during the breeding-season, and those which never have a hood at any time. In all the members of both of these groups the immature birds have a dark band across the rectrices, which disappears as they approach maturity. Several representatives of each of these groups also inhabit the southern hemisphere-Larus cirrhocephalus of South America, and its close ally L. phaocephalus of South Africa, L. maculipennis, L. glaucodes, and L. serranus of South America, belonging to the former ; L. dominicanus, found from New Zealand to South America (by way of the Cape of Good Hope, not through the South Pacific), L. bulleri, L. scopulinus, L. nova-hol-landia, and L. hartlaubii, found at or between New Zealand and the Cape of Good Hope, belonging to the latter group. But it is only in the Pacific (merely including in that area the desolate islands of South Shetland, the Falklands, and a portion of Patagonia near the eastern entrance of the Straits of Magellan) that we find several species of Gulls which agree with the other forms in having a band across the rectrices in the immature stage, but differ from them in many other respects. Most of these species are of a coarse heavy build, and have a tendency to a sooty hue on the underparts ; but their principal characteristic is the presence of a more or less defined hood in the immature stage, which is generally lost in the adult plumage. L. scoresbii, which extends beyond the Pacific to the Falklands, varies least in this respect from the general type of Gulls ; it has a well-defined hood in youth, but loses the hood with the disappearance of the bar on the tail, which becomes white. Its range is but little beyond that of the Cape-Horn current. Larus belcheri, distributed along the whole coast-line of Chili and Peru washed by Humboldt's current of cold water, has a hood in youth only ; but it has a barred tail at all ages, the black predominating over the white. The species most nearly resembling it in the adult plumage is Larus crassirostris, of the Pacific coasts of Japan and China, in which, however, the amount of black and white in the rectrices is nearly equal; nor has the young so well-marked a hood ; its mantle also is lighter, and its other characteristics are so far modified as to make it intermediate between the Old-World and the South-Pacific Gulls. The line of communication of the ancestor of these forms, which now constitute |