Quantifying the success of prey crypsis, aposematism and evasiveness in avoiding predators’ attack

Antipredator defences typically act at distinct stages of the predation sequence—encounter, identification, approach, and subjugation. However, their effectiveness has rarely been quantified and compared simultaneously in wild predator-prey systems. We conducted a study in Peru, where we installed aviaries at two localities and recorded the responses of wild avian predators to three types of antipredator defences—crypsis, aposematism, and evasiveness—expressed by three butterfly species. The study included both immature and adult birds from insectivorous species in forest and urban environments. We tested the theoretical expectations that cryptic butterflies (Nymphalidae: Euptychiina) were rarely detected, aposematic Heliconius (Nymphalidae: Heliconiinae) were often sighted but seldom attacked, and evasive Spicauda (Hesperiidae: Eudaminae) were frequently detected and attacked but evaded capture at higher rates. Despite these distinct defensive strategies, mortality rates among prey types were largely similar, but predator life stage strongly influenced defence effectiveness. Immature birds were more likely to attack Heliconius , possibly reflecting a lack of learned avoidance for aposematic signals. Additionally, predator family influenced predation patterns, with more skilled insectivores (e.g., Vireonidae) showing higher capture success against defended prey. These findings illuminate the evolutionary pressures that shape predator behaviour and prey defences in tropical ecosystems, where high predator diversity possibly maintains the coexistence of multiple defensive strategies. The observed similar mortality rates underscore the adaptive value of these defences, as they collectively distribute the total predation pressure across prey species.