The Influence of Roost-Cavity Availability on Flock Size in the Redbilled Woodhoopoephoeniculus Purpureus

Summary Du Plessis, M.A. 1989. The influence of roost-cavity availability on flock size in the Redbilled Woodhoopoe Phoeniculus purpureus. Ostrich suppl. 14: 97–104. The availability of roost-cavities to Redbilled Woodhoopoes Phoeniculus purpureus was compared between two different populations in the eastern Cape Province of South Africa in order to identify the influence that this resource may have in promoting group-living. Food availability and predatory pressure appeared to be similar at the two sites, but roost-cavity availability differed significantly. The latter was attributable to differences in the vegetation composition of territories at the different sites. Inland birds formed significantly larger flocks than coastal birds. The presence of marginal habitat (in terms of cavity availability) at the coastal site may have ensured an outlet for young birds from their natal territories, resulting in smaller flock sizes, whereas lack of such habitat at the inland site may have resulted in forced retention of young in their natal territories and hence larger flock sizes. It is suggested that variability in Redbilled Woodhoopoe social and reproductive behaviour reflects environmental selection pressures, in the form of roost-cavity availability, with a reduction in cavity availability leading to increased group size.