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Show Sights and Sounds of the Winged World 725 Drawn by Walter A. Weber A Bird's-eye View of the World This Red-shouldered Hawk looks straight ahead with both eyes together; this binocular vision (page 723) covers the dark central band with the central spot (t) of sharpest sight. Two circles (c) at either side designate the acute field of monocular vision for each eye alone; the gray band from x to x marks a segment of total arc of vision in this bird. This drawing was adapted from a sketch by Gordon Lynn Walls in The Vertebrate Eye, published by the Cranbrook Institute of Science. dents, Victor Coles, attempted to settle the age-old question of whether turkey buzzards find their food by sight or smell. John James Audubon thought he had settled it when buzzards were unaware of a carcass he had concealed under a canvas but were attracted by his painting of a dead sheep. Later observers, however, discovered that buzzards often found carcasses concealed in wood-chuck holes or under boxes. After watching the buzzards of Barro Colorado Island, Canal Zone, discover the hiding place of some dead fish concealed under a thatched roof, Frank Chapman became convinced that they must have a keen sense of smell.* For two years we housed Victor Coles' three buzzards while he carried on a series of experiments testing their olfactory sense. He has not yet published his thesis, but before he received his degree he had convinced even the most skeptical that his captive buzzards' sense of smell was so poor as to be of little more use to them than their sense of taste in locating food. The olfactory lobe of the brain is very small in buzzards, as in all other birds, and the turbinal bones of the nose over which are spread the olfactory membrane and nerves are only partially covered with the sensory tissue. The buzzard's vision, on the other hand, is exceedingly keen. Doubtless they have learned through experience to associate buzzing flies and crawling beetles with their type of repast, even when the carrion itself is not visible from the air. Their poor sense of smell spares them a discomfort that might become unbearable even to a scavenger. One of the favorite foods of the horned owl is the common skunk. Probably the skunk's unique method of defense, so effective as far as man and dog are concerned, is scant protection against the night marauder with no sense of smell. Psychologists tell us that there are only four tastes-sweet, sour, bitter, and salt-and that all the rest of those delectable sensations a good chef invokes are really smells. If that be so, the birds' poorly developed sense of smell may account for their strange choice of foods. If worms were only sweet or sour and all bugs tasted the same, we could close our eyes and never starve in the jungle. Why Birds Eat F ew Japanese Beetles Some birds are guided by sight, touch, and experience in their selection of food. Only recently rodent exterminators have learned that poisoned grain stained blue or red will not be touched by birds but will be devoured, despite its coloring, by such creatures as rats and mice that find their food to a great extent by smell. The Japanese beetle looks different from the *See "Who Treads Our Trails?" by Frank M. Chapman, NATIONAL GEOGRAPHIC MAGAZINE, September, 1927. |