Birds have no impact on folivorous insect guilds on a montane willow

Abstract

We examined the impact of avian predators on the community of insects feeding on Lemmon's willow, Salix lemmonii, at Carman Valley, California. Salix lemmonii supports a diverse assemblage of insect species that feed in either a concealed or an exposed manner on leaves by mining, tying, curling, galling, skeletonizing, or chewing. We tested the hypothesis that there are guild specific differences in the effects of avian predators on concealed and exposed‐feeding folivores. We compared the feeding damage and frequency of each guild in the presence and absence of avian predators. Contrary to most studies of the effects of avian predators on folivorous insects, birds failed to reduce significantly the frequency of or feeding damage caused by exposed‐feeding insects during 1999 and 2000. Chewing insects, which accounted for the majority of foliar damage by exposed‐feeding insects, inflicted slightly more damage and skeletonizing insects slightly less damage in the presence of birds. We also observed no reduction in the frequency of concealed‐feeding insects in the presence of avian predators; rather three out of four guilds were slightly more common in the presence of avian predators. While the abundance of foliage gleaning birds at the study site was slightly lower than the average for the past nine years, we interpret our results to indicate a true lack of an effect of avian predators on the community of folivorous insects on S. lemmonii. Future inquiry into the effects of avian predators on folivorous insects should focus on determining under what circumstances birds will or will not suppress guilds of folivorous insects.