Complementary approaches to measure predation pressure on butterfly populations in Australia

Predation pressure is a major force driving the evolution of anti-predatory traits, yet quantifying its intensity in the wild remains difficult. In this study, we combined three complementary methods to evaluate predation risk in Australian butterfly communities: assessing wing damage on wild butterflies, monitoring attacks on artificial butterfly replicas, and surveying bird communities. Across eight sites in Sydney, Australia, we recorded wing damage on 1070 free-living butterflies from five families, assessed attacks on 1600 butterfly replicas, and surveyed local bird diversity. Of the wild butterflies, 807 showed wing damage, with 169 individuals (16% of all butterflies) exhibiting patterns consistent with bird attacks. Among replicas, 114 (7%) showed evidence of predation, of which 31 (2% of all replicas) were likely to be attacked by birds. Predation on wild butterflies was most strongly associated with bird community composition, bird density, and butterfly size (wingspan), while replica attacks were influenced primarily by bird community composition and density. Our results suggest that butterfly wing damage and replica attacks data provide complementary, but not interchangeable, insights into predation risk. When integrated, they offer a more robust picture of true predation pressure. Our results underscore the critical role of bird community structure in shaping predation risk - an important consideration for any method used to assess predation in natural prey communities.