Social Sexual, and Pseudosexual Behavior of the Blue-bellied Roller, Coracias cyanogaster: The Consequences of Crowding or Concentration. Smithsonian Contributions to Zoology, Number 491

摘要

Blue-bellied Rollers (Coracias cyanogaster) occur in West Africa. They are typical of Coracias species in being sit-and-wait predators. They pounce upon relatively large prey (arthropods and vertebrates) in low, sparse vegetation or on bare ground. They differ from their closest relatives, other species of the same genus, in preferring humid or semi-humid habitats. In West Africa, such habitats are naturally forested. Blue-bellied Rollers often perch high in trees. Still, they prefer to pounce low. This means, in effect, that they are dependent upon clearings to some appreciable and significant extent. Patches of bare earth and sparse vegetation probably were few and scattered before the spread of agriculture. In these earlier circumstances, Blue-bellied Rollers must have had to concentrate upon whatever open spaces were available. They may have been more crowded on a restricted local level than other species of rollers. All Coracias are large, powerful, and aggressive. Concentration and crowding must have been difficult to manage or to support. The ancestors of modern Blue-bellied Rollers would seem to have evolved several behavioral mechanisms to cope with their problem. They may have become more tolerant of conspecifics than their relatives. In the Basse Casamance region of Senegal and perhaps other areas, they have also developed the habit, unique among rollers, of performing pseudocopulations, reverse mountings, sometimes with apparent cloacal contacts, sometimes repeatedly. Sexually-derived patterns are potentially capable of being used to control agonistic encounters irrespective of actual sex. They seem to do so in two ways. They can function as threat. They also canalize aggression to minimize the risks of contact fighting with neighbors and intruders. Adaptations to forested conditions have survived, even though much of the land has been largely cleared for centuries or perhaps thousands of years.