POLYGYNY AND BREEDING ECOLOGY OF THE CETTI'S WARBLER <i>CETTIA CETTI</i>

Abstract

Summary Male Cetti's Warblers bred simultaneously with up to three females. Harem size was correlated with size of male but not of his territory. Males occupied large usually exclusive ranges and devoted much time to patrolling and singing often far from their nests. Incubation was solely by the female who also provided most to all of the food for the young. Incubation and fledging periods were prolonged compared with similar sized birds but first nests were unusually successful. Polygynously mated females laid larger clutches than monogamous ones. Males with fewer females took a greater share of feeding but chick growth and survival were not impaired by polygyny, nor did foods brought to the young differ accordingly. The existence of this unusual breeding system is discussed with emphasis on the co‐evolution of sexual dimorphism and non‐equal sex ratios resulting from malemale competition. It is postulated that the linear dispersion of its habitat may especially have favoured operation of the Verner‐Orians polygyny model in the evolutionary history of the Cetti's Warbler.