Social Faciltation in Weaverbirds: Effects of Varying the Sex Ratio

Experimental colonies of African Village Weaverbirds (Ploceus cucullatus cucullatus) in large outdoor aviaries at Los Angeles were observed. When males were caged singly, each with several females, these males expanded their territorial holdings and had more nests accepted by the females than was the case when other males were present. When several additional males were present during the height of the breeding season, the resident males showed little or no change in their rate of nest—building, but with extra males present more fresh nests became available and more females accepted nests. When the breeding season started to decline, adding more males stimulated renewed onset of nest—building by resident males. When the number of females in each colony was increased four times, the average rate at which the males built and tore down their nests about doubled while the frequency with which the males gave the nest—advertisement display to untamed females tripled. But at the same time the males built on the average only half as many nests per female, reflecting an effective reduction in competition between males for mates when an abundance of females was present.