Do tropical birds avoid evasive prey? An experimental study in Ecuadorian avian communities

The effect of predator behaviours on the evolution of colour pattern has been extensively studied in chemically defended prey but much less so in evasive prey, although similar selection regimes might be at play. Most previous work on the recognition and learning of colour patterns by predators has relied on experiments with few model predator species, preventing a proper assessment of how natural predator communities shape the evolution of prey signals. Here, we investigate predation on evasive iridescent blue Morpho helenor butterflies by wild avian communities in a tropical forest, using artificial butterflies exposed to natural bird assemblages attracted to insect-light traps in the field. We presented five prey types: evasive (local and exotic Morpho), cryptic, palatable-control and unpalatable-control. We recorded attacks from 43 different bird species, and compared attack latency, attack order and predation exerted by different birds on different prey types. Most birds avoided evasive and defended prey, but attack responses differed depending on their levels of specialization towards insect prey. Avoidance of conspicuous coloured prey was more prevalent in specialist flight-feeding, invertivorous birds, whereas more opportunistic treehunter and frugivorous guilds had weaker discrimination. Exotic and local evasive iridescent blue Morphos experienced similar predation rates, suggesting a generalization of iridescent blue signals associated with evasiveness by most birds. Finally, contrasting selection on ventral vs. dorsal patterns was detected in M. helenor, where cryptic ventral surfaces were exposed to attack by ground-foraging birds, whereas conspicuous iridescent blue coloration displayed during flight is associated with reduced attack rates. By revealing potential differences in the responses of specialist and generalist predators, this study highlights the importance of accounting for diversity of predator traits and behaviours when investigating the evolution of aposematism, mimicry, and other anti-predator adaptations.