Diver

Diver, a name that when applied to a bird is commonly used in a sense even more vague than that of loom, several of the sea ducks or Fuligulinae and mergansers being frequently so called, to say nothing of certain of the auks or Alcidae and grebes; but in English ornithological works the term diver is generally restricted to the Family known as Colymbidae, a very well-marked group of aquatic birds, possessing great, though not exceptional, powers of submergence, and consisting of a single genus Colymbus which is composed of three, or at most four, species, all confined to the northern hemisphere. This Family belongs to the Cecomorphae of T. H. Huxley, and is usually supposed to occupy a place between the Alcidae and Podicipedidae; but to which of these groups it is most closely related is undecided. Professor Brandt in 1837 (Beitr. Naturgesch. Vögel, pp. 124-132) pointed out the osteological differences of the grebes and the divers, urging the affinity of the latter to the auks; while, thirty years later, Professor Alph. Milne-Edwards (Ois. foss. France, i. pp. 279-283) inclined to the opposite view, chiefly relying on the similarity of a peculiar formation of the tibia in the grebes and divers,1 which indeed is very remarkable, and, in the latter group, attracted the attention of Willughby more than 230 years ago. On the other hand Professor Brandt, and Rudolph Wagner shortly after (Naumann’s Vögel Deutschlands, ix. p. 683, xii. p. 395), had already shown that the structure of the knee-joint in the grebes and divers differs in that the former have a distinct and singularly formed patella (which is undeveloped in the latter) in addition to the prolonged, pyramidally formed, procnemial process—which last may, from its exaggeration, be regarded as a character almost peculiar to these two groups.2 The evidence furnished by oology and the newly-hatched young seems to favour Brandt’s views. The abortion of the rectrices in the gerbes, while these feathers are fairly developed in the divers, is another point that helps to separate the two Families.

The commonest species of Colymbus is C. septentrionalis, known as the red-throated diver from an elongated patch of dark bay which distinguishes the throat of the adult in summer dress. Immature birds want the bay patch, and have the back so much more spotted that they are commonly known as “speckled divers.” Next in size is the black-throated diver, C. arcticus, having a light grey head and a gular patch of purplish-black, above which is a semicollar of white striped vertically with black. Still bigger is the great northern diver, C. glacialis or torquatus, with a glossy black head and neck, two semicollars of white and black vertical stripes, and nearly the whole of the black back and upper surface of the wings beautifully marked with white spots, varying in size and arranged in belts.3 Closely resembling this bird, so as to be most easily distinguished from it by its yellow bill, is C. adamsi. The divers live chiefly on fish, and are of eminently marine habit, though invariably resorting for the purpose of breeding to freshwater lakes, where they lay two dark brown eggs on the very brink; but they are not unfrequently found far from the sea, being either driven inland by stress of weather, or exhausted in their migrations. Like most birds of their build, they chiefly trust to swimming, whether submerged or on the surface, as a means of progress, but once on the wing their flight is strong and they can mount to a great height. In winter their range is too extensive and varied to be here defined, though it is believed never to pass, and in few directions to approach, the northern tropic; but the geographical distribution of the several forms in summer requires mention. While C. septentrionalis inhabits the north temperate zone of both hemispheres, C. arcticus breeds in suitable places from the Hebrides to Scandinavia, and across the Russian empire, it would seem, to Japan, reappearing in the north-west of North America,4 though its eastern limit on that continent cannot be definitely laid down; but it is not found in Greenland, Iceland, Shetland or Orkney. C. glacialis, on the contrary, breeds throughout the north-eastern part of Canada, in Greenland and in Iceland. It has been said to do so in Scotland as well as in Norway, but the assertion seems to lack positive proof, and it may be doubted whether, with the exception of Iceland, it is indigenous to the Old World,5 since the form observed in North-eastern Asia is evidently that which has been called C. adamsi, and is also found in North-western America; but it may be remarked that one example of this form has been taken in England (Proc. Zool. Society, 1859, p. 206) and at least one in Norway (Nyt Mag. for Naturvidenskaberne, 1877, p. 134).