An «ad hoc» association of hornbills, starlings, coucals, and other birds

Abstract

An association of several different species of birds was observed at M Bour in western Sénégal in early 1977. The two species of greatest social weight were the Longtailed Glossy Starling (Lamprotornis caudatus) and the Redbilled Hornbill (Tockus erythrorhynchus) . Individuals of both species were gregarious among themselves. The Redbilled Hornbills also were attractive to coucals (Centropus senegalensis), Hoopoes (Upupa epops), and Longtailed Shrikes (Corvinella corvina). They were themselves attracted to the starlings. The net result of the interactions among these species was the daily formation of large mixed flocks. The flocks were sometimes visited by birds such as Phoeniculus purpureus and Tockus nasutus, but they were ignored by many other species in the neighborhood. The benefits derived from the habit of associating in mixed flocks were obviously varied. Mutual help in finding or flushing food seemed to be less important, in the local circumstances, than protection against predators or the regulation of competition by monitoring of rivals. Some aspects of the behavior involved in the formation and maintenance of the mixed flocks were distinctive. They may be adaptations to facilitate social flexibility in the short term and over small distances. Opportunism would be expected in the rigorous and fluctuating environment of most of Sénégal. The species that associated with one another at M Bour are known to show other kinds of interspecific behavior in other areas and/or at other seasons, not far away in either space or time. Some of the variation may be due to individual choice. Among the apparent consequences or correlates of this opportunism are the absence of certain kinds of visual signals, the partial suppression of acoustic signals, and a reliance upon many and probably complex clues for recognition of potential companions. The mechanisms of such interactions probably are highly specialized.