songs

This phenomenon, known as rapid food-avoidance conditioning, is so strongly wired into many species that a single exposure to a toxic substance is usually sufficient to train an animal for life. The same sorts of biases are observed in nearly every species. Pigeons, for instance, readily learn to peck when food is the reward, but not to hop on a treadle for a meal; on the other hand, it is virtually impossible to teach a bird to peck to avoid danger, but they learn treadle hopping in dangerous situations easily. Such biases make sense in the context of an animal's natural history; pigeons, for example, normally obtain food with the beak rather than the feet, and react to danger with their feet . Perhaps the example of complex programmed learning understood in most complete detail is song learning in birds. Some species, such as doves, are born wired to produce their species-specific coos, and no amount of exposure to the songs of other species or the absence of their own has any effect. The same is true for the repertoire of 20 or so simple calls that virtually all birds use to communicate messages such as hunger or danger. The elaborate songs of songbirds, however, are often heavily influenced by learning. A bird reared in isolation, for example, sings a very simple outline of the sort of song that develops naturally in the wild.

Yet song learning shows all the characteristics of imprinting. Usually a critical period exists during which the birds learn while they are young. Exactly what is learned-what a songbird chooses to copy from the world of sound around it-is restricted to the songs of its own species. Hence, a white-crowned sparrow, when subjected to a medley of songs of various species, will unerringly pick out its own and commit it to memory. The recognition of the specific song is based on acoustic sign stimuli. Despite its obvious constraints, song learning permits considerable latitude: Any song will do as long as it has a few essential features. Because the memorization is not quite perfect and admits some flexibility, the songs of many birds have developed regional dialects and serve as vehicles for a kind of cultural behavior. A far more dramatic example of programmed cultural learning in birds is seen in the transmission of knowledge about predators. Most birds are subject to two sorts of danger: They may be attacked directly by birds of prey, or their helpless young may be eaten by nest predators. When they see birds of prey, birds regularly give a specific, whistlelike alarm call that signals the need to hide.