Comparison of Vocal Signals of Three Species of African Finches

Abstract

African finches of a monophyletic group in the Passeridae nest in colonies with roofed nests thatched of dry grass-stems. Vocal signals are described, with the aid of sonograms, 13 for the white-browed sparrow-weaver (Plocepasser mahali)(Pm), 13 for the grey-capped social weaver (Pseudonigrita arnaudi) (Pa), and 20 for the sociable weaver (Philetairus socius) (Ps). These vocal signals fall into general categories, as is true for most birds, of alarm calls, agonistic behavior, and courtship and mating signals, parent-young relations, and flock contact calls. These three species illustrate the principle of adaptive specialization of vocal signals. Pm differs from the others in having a loud dawn song, a whispered version of this song, and also a loud vocalization frequently given in defense of a group territory within which the birds forage. Pa and Ps differ from Pm in defending only the immediate vicinity of the nest or nest chamber, in foraging in large flocks on neutral ground often well away from the colony nest trees, and have special flock calls. In Pa, the territorial call is used mainly to announce arrival at its nest, and song is rare or absent in this species. Ps, which lives in a large, apartmentstyle communal nest, has the most diversified repertoire, especially of social contact calls. Convergent evolution of vocal signals and social organization with unrelated families gives some idea of the selection pressures in the evolution of these signals.