Butterfly visual characteristics and ontogeny of responses to butterflies by a specialized tropical bird

Abstract

The responses of two adult and three hand-reared, naive young rufous-tailed jacamars (Galbula ruficauda) to local butterflies were studied in feeding experiments. Four behavioural characteristics distinguish jacamars from other less specialized avian predators: (1) Exposed to butterflies for the first time, naive young jacamars would attack butterflies without showing signs of inhibition. Unacceptable butterflies, once captured, were taste-rejected quickly, and most survived the sampling. The few presumably unacceptable butterflies consumed by the birds were not observed to cause vomiting. (2) After gaining some familiarity with butterflies, young birds, like the adults, developed a reluctance to attack. They visually rejected certain classes of butterflies, often failing to attack them during an entire four-hour feeding trial. However, occasional attacks were made on butterflies in these ‘rejected’ classes. When this did occur, the insects proved to be actually easier to catch than those that were more often attacked. Once captured, however, the majority of these butterflies were taste-rejected. (3) For a given butterfly species, most individuals were either consumed or rejected. Thus, each species could be clearly classified as either acceptable or unacceptable to the jacamars. This consistency in jacamar responses resulted in a bimodal acceptability distribution of sympatric butterflies. (4) Young jacamars were capable of rapid associative learning and their responses were closely associated with butterfly visual characteristics in which colour pattern, flight behaviour, and morphology were also closely correlated. Thus, a single butterfly morphological parameter termed body shape (body length/thoracic diameter ratio) can adequately predict the feeding responses of jacamars. Visually detectable traits associated with butterflies possessing chemical defences may represent a balance between the need to signal unambiguously to specialized and/or experienced predators and the need to escape attacks by generalized and/or opportunistic predators. Since the proportion of specialized predators is higher in the tropical rainforest than in other habitat types, we expect greater divergence of morphological and behavioural characteristics between palatable and unpalatable butterflies in rainforest habitats.