Measuring predation pressure on butterfly populations

Predation pressure selectively shapes the evolution of anti-predatory traits. Understanding predation pressure within the butterfly-bird system is difficult as direct predation is rare to observe. Different methods are therefore often utilized to measure predation pressure on butterflies. We tested the appropriateness of four such methods. We compared actual butterfly wing damage, butterfly clay-model damage, and predator diversity and density. Butterflies were sampled to determine the wing damage rates by birds. Butterfly model deployments and surveys were carried out to assess the model damage rates by birds. Bird surveys were conducted to assess predator diversity and density. Wing damage was closely related to both bird diversity and density while model attacks did not show such a close relationship to either bird diversity or density. Thus, the actual wing damage, together with bird surveys is an appropriate and logistically achievable method to estimate predation pressure on butterflies. We also investigated the variation in wing area damage by birds within butterfly families. We found that butterfly hindwings were damaged more than forewings, but wing area damage was independent of butterfly body size. These data can provide additional information about the predation interaction between butterflies and birds.