Rufous-tailed jacamars and aposematic butterflies: do older birds attack novel prey?

Although avian predators are thought to drive the evolution of warning-color mimicry in butterflies, few empirical studies directly address this assumption from the predator's perspective. Heliconius butterflies are textbook examples of Mullerian mimicry, with perhaps the most remarkable example being the Heliconius erato and Heliconius melpomene mimicry complex. Rufous-tailed jacamars, Galbula ruficauda (Galbulidae), are well-known butterfly predators and provide an excellent study organism to investigate patterns of attack behavior in warning-colored butterflies. I investigated patterns of attack behavior by presenting three aposematic butterflies to wild-caught jacamars in a cage trial in Venezuela. I presented 80 jacamars with three Heliconius butterflies: an unaltered wing pattern (local morph) and two altered wing patterns (novel morphs). Twenty-one of 40 males and 8 of 40 females attacked a butterfly with a novel wing pattern. Of the morphological variables measured, tail length was the only significant predictor of attack behavior. Individuals with relatively longer tails attacked novel butterflies more frequently than shorter tailed individuals. Because tail length tended to increase between seasons, results suggest that older birds are more likely to attack novel aposematic prey than are young birds, contrary to the expectations that younger adult birds (i.e., more likely to be naive) would attack novel Heliconius more frequently than older birds. Overall results support the role of specialized avian predators, like jacamars, as important agents in the evolution of warning-color mimicry in butterflies and the need to investigate different age classes of birds in mimicry studies.