AMPHIBIOUS LIZARDS. SNAKES, BIRDS 439 



better) under water as in the air — such birds as the loons, grebes, snake- 

 birds, auks, and penguins, all of which pursue and catch fishes. The 

 penguins cannot fly in the air at all; and most of us have seen how much 

 of a chore it is for a loon to 'take off'. The cormorants are also speedy 

 fish-chasers, though they perhaps use their feet more than their wings. 

 Still other birds swim on the surface, and up-end to feed on plants or 

 fishes in the water beneath: ducks, coots, mergansers, etc. A host of 

 birds, most of which can swim on the surface to rest and sometimes dive 

 from the surface, have the habit of flying over water and plunging into 

 it momentarily to grasp a finny prey : pelicans, gulls, terns, shearwaters, 

 petrels, gannets, boobies, albatrosses, ospreys, sea-eagles and so on — 

 and one of the cormorants, the Peruvian guano-bird. 



Three kinds of birds have particularly unusual water-habits — the tor- 

 rent ducks, the dippers, and the kingfishers. The kingfishers may plunge 

 from the wing, but more commonly do so from a perch, and thus come 

 between the flying fishers and the tall waders like the herons, whose 

 perches are their own long legs. Their eyes, as we shall see shortly, are 

 a little reminiscent of those of Anableps. The dippers are an especial 

 phenomenon, for though no birds are so thoroughly wedded to water 

 (they will not even fly over dry land!) they are regarded by ornitholo- 

 gists as having no adaptations whatever for water. The dipper or water- 

 ouzel is simply a thrush which walks and flies unconcernedly under water 

 to find his insect food, holding himself down when necessary by grasping 

 stones with his feet, which even lack the ubiquitous webs of other water 

 birds. His eyes have never been studied, but will almost certainly prove 

 to have amphibious adaptations even though such are lacking every- 

 where else in the body. 



In general, the eyes of all of these birds are built primarily for aerial 

 vision. The extent to which water birds have attained underwater seeing- 

 ability goes largely with the duration of their underwater periods, and 

 hence, naturally, with their general bodily modification for submerged 

 activity. Thus, the penguins head the list with eyes which are entirely 

 devoted to water vision, with highly responsive pupils and with no special 

 range of accommodation or other device to make them very useful in 

 air, in which they are notoriously myopic. It has often been pointed out 

 that a swimming penguin is quite dolphin-like in its streamlined form, 

 with even the same color-pattern — black above and white below. Pen- 

 guins are so completely adapted to water that they have hair-like feathers 

 in enormous numbers, a whale-like blubber for heat insulation, and are 



