ABSTRACT
Birds, like other animals, are endowed with diverse structural and behavioral devices to escape from or fend off their predators. As a result of coevolution of prey and predator, behavioral devices for predator avoidance may become part of the prey species' behavioral repertoire. Predator avoidance, for instance, is often finely tuned to sympatric predators and is preprogrammed so that individual learning is unnecessary (Curio, 1969, 1975; Giles, 1984; Seghers, 1970, 1973). Individual learning of predator avoidance may even be unfeasible because of its deadly cost (Smith, 1975, 1977). When the threat from predators is relatively unpredictable, for example, as the result of invasion by a previously absent predator species (see Robertson & Norman, 1977, for a brood parasite; Diamond, 1985) or of a change in hunting behavior of a sympatric, hitherto innocuous species (Steiniger, 1950), phenotypic plasticity can come to safeguard prey. One way to achieve learning to avoid a particular predator is by cultural transmission of avoidance of predator-associated stimuli, one of many forms of tradition in animals (see Mainardi, 1980). Formation of single species or multispecies flocks, an ingredient of predator harassment, would appear particularly conducive to this sort of learning.
