National Geographic : 1962 Apr
a bird inherits the drive to do something but not the ability to do it. To prove the point, Dr. Dilger crossbred different species of African lovebirds. Fe males of all these species cut narrow strips of bark or leaves for nest building. In captiv ity, they will cut strips from wrapping paper instead (opposite, below). But the females vary in their manner of flying the strips to the nest site. Some carry with their bills, while others tuck one end of each strip under feathers of the body and fly home with perhaps a dozen strips trailing like streamers. Aware of these differences, Dr. Dilger wondered: What happens when "nontuckers" are mated to "tuckers"? The hybrids inherit the urge to tuck but not the ability to hold. They may cut and tuck for twenty minutes without understand ing that their feathers cannot hold the strips. Finally they carry off a single strip in the bill, but when they return, they try to tuck again and again without success. Over a period of years, however, they gradually learn to carry the strips in their bills and virtually abandon the tucking. Young Birds Reared in Soundless World Jim Hartshorne, one of our graduate stu dents, applied his ingenuity to the songs of birds. He concerned himself with the basic call notes, such as distress calls and begging cries, and especially with the song character istic of a species, called the primary, or true, song, which the male sings to attract females and to challenge other males near his terri tory. Are the call notes and true song inher- KODACHROMESBY DAVID G. ALLEN L) N.G.b . Horned grebe, or hell-diver, reveals its under water table manners. Glass tank shows how the bird catches and swallows its prey. Minnows scatter as the grebe, in winter plum age, swoops in. Photograph demonstrates that the hell-diver does not use wings underwater, but kicks with the broad lobes of its toes.