Nesting success of rufous-naped wrens (Campylorhynchus rufinucha) is greater near wasp nests

Summary Rufous-naped wrens (Campylorhynchus rufinucha) in northwestern Costa Rica build breeding nests most frequently in ant-acacia trees (Acacia collinsii) and occasionally near wasp nests in ant-acacia trees. By moving occupied wasp nests (Polybia rejecta) to randomly chosen ant-acacia trees with wren nests, I tested the hypothesis that wrens nesting near wasp nests were more likely to fledge young than wrens not nesting near wasp nests. Wrens whose nests were near experimentally relocated wasp nests were significantly more likely to fledge young (37.5% of 16 attempts in 1987 and 75% of 12 attempts in 1988) than were wrens whose nests had no wasp nests placed near them (0% of 16 attempts in 1987 and 20% of 15 attempts in 1988). In 15 cases, repeated nesting attempts occurred in the same trees both with and without experimentally-placed wasp nests. Analysis of these data allowed a comparison of the effect of wasp nests on fledging success while differences among trees were controlled. Within the same tree, nesting attempts associated with wasp nests were significantly more likely to fledge young than nesting attempts without wasp nests. Predation was the primary cause of nest failure, and within forest, white-faced monkeys (Cebus capucinus) were the most important predators. The difference in success of wren nests with and without wasps and observations of predators indicate that enhancement of fledging success was due to deterrence of predatory vertebrates by wasps.