Others indulged in repetitive head movements, while two birds developed a complicated pendulum motion of the head and body.
As soon as the number of "twigs" becomes too large, however, the bird develops an interest in them, attacks some real twigs, and also finds some caterpillars.
In captivity, many birds develop Feather Destructive Behavior as a result of conditions including lack of psychological and emotional stimulation, stress, lack of companionship, and limited freedom.
This might have caused the birds to develop a preference for interactions with long-term experimenters (Davis, 2002).
Most birds develop immunities to the virus within days of infection and are no longer carriers.
Before they die, the birds develop major hemorrhages, with blood streaming from their cloacas and beaks.
The crisis facing vultures is exacerbated by the fact that the birds develop very slowly.
Species whose song acquisition involves a great deal of individual learning are probably those in which individual birds develop slightly different songs.
Young birds develop the method employed by their parents, but experiments in which chicks were fostered by adults with a different habit from that of the natural parents have established that this behaviour is not genetically determined.
In 1837, a German anatomist showed that ear-bones in mammals, like the jaw-joint bones in frogs and birds, develop from cartilage in the first two of the visceral arches septing successive gill slits in the tadpole-like stage of their respective embryos, a phenomenon that only makes sense in the light of their common ancestry.
