Spatial parameters and interspecific social relations: Some differences between birds and fishes

Abstract

Interspecific social relations tend to be complex among coral reef fishes and among birds of tropical forests and scrub. Some relations are similar in the two groups, but others are not. The published literature suggests that social mimicry involving bright colors is much more common among birds than among reef fishes. This difference may be correlated with the media in which the animals live. In air, most birds have to move from point to point, from one perch or landing site to another. Numbers of points are not unlimited. Individuals of different species of birds are often, therefore, brought into close contact with one another. Social mimicry is an adaptation to facilitate or regulate such encounters, a sort of “automatic” or “fail safe” device. In water, at least of appreciable depth, fishes have greater freedom of movement. Many of them can move continuously and gradually in any direction, as far or as near as may be desirable in the circumstances. They are not as closely bound to particular points as are birds. They can encourage or discourage encounters by subtle modulations of advance and retreat. They have less need for relatively crude automatic devices than do birds. The differing frequencies of bright or conspicuous social mimicry in birds and in coral reef fishes (and perhaps in other groups of animals such as ants and cephalopods) would suggest that great flexibility of movement in space is preferred to mimicry as a regulator of interspecific social relations whenever it is feasible.