BIRDS' KEEN SIGHT

Evening Star, Issue 19764, 14 January 1928, Page 19

BIRDS' KEEN SIGHT

IS IT EXAGGERATEDF The ‘ Scientific American ’ recently published an article on the vision of insects, and a correspondent was prompted to write suggesting a comparison of the quality of vision of good human eyes with that of certain birds, notably hawks, eagles, and buzzards) as well as with that of insects. Although we suspected that the suggestion would prove fruitless (says the journal), for we believe science has not yet fully investigated the subject of eyesight in birds, we referred Mr Olmsted’s letter to Dr Alexander Wetmore, assistant secretary of the Smithsonian Institution and president of the American Ornithologists’ Union. Dr Wctmore’s interesting reply follows ; “Vision in birds is remarkable to me for its accommodation that permits, for example, a sparrow to distinguish a seed within an inch of the end of its bill, and at the .same time allows it to distinguish a hawk soaring high overhead. Most birds have a distinct faculty , for two kinds of vision. One monocular, in which both eyes work independently, and the other binocular, in which both concentrate on the same object. There are in most species two distinct centres of sharp vision for these two types of sight.

“Much is current in literature regarding the keenness of sight evidenced in vultures where, according to the popular concept, the smallest fragment of food is seen by birds so high in the air as to be practically invisible to humans. During approximately thirty years of observation throughout the New World, from this country south to Patagonia, I confess that 1 have never seen anything of the kind. It is my candid opinion that vultures soar aloft merely for the pleasure of a joy ride in the ether, and when they arc actually hunting for food they are sweeping in great circles near the earth in loops that bring them down within a few yards of any object that seems to promise food. Through this incessant quartering they distinguish easily snakes, mice, or dead creatures of any kind, and descend to feed. Larger creatures, of course, can be seen from a. much greater distance, but I do not place the slightest credence in their seeing small bodies at any great distance. “It has been my common experience when stopping to rest or to examine some bird or other creature that I. had shot for a museum specimen to have within a few momenta a turkfcy, vulture, or even a condor come sweeping overhead looking down curiously to see what I was about. Unquestionably such birds have come to learn that man is an animal to be kept under observation, and that when he stops he is liable' to leave behind him something that may serve for food. I have even had the yellow-headed vulture, in tho South American Chaco, fly in to alight above me in a heavy forest in which I had momentarily disappeared from view. ‘ ‘ Many vultures are gregarious to a point where they assemble nightly in central roosts from which they spread out to search for food. In their quartering back ami forth they are frequently in sight of one another, so that when one descends to feed, others are soon tracking to it, particularly to carcasses of considerable size. . I do not see in this, however, any. indication of the wonderful eyesight usually ascribed to them, hut rather merely an example of their careful search for sustenance.”