BUTTERFLY VISUAL CHARACTERISTICS AND ONTOGENY OF RESPONSES TO BUTTERFLIES BY A SPECIALIZED TROPICAL BIRD

The responses of two adult and three band-reared, naive young rufous-t ailed jacamars (Galbula ruficauda) to local butterflies were studied i n feeding experiments. Four behavioural characteristics distinguish ja camars from other less specialized avian predators: (1) Exposed to but terflies for the first time, naive young jacamars would attack butterf lies without showing signs of inhibition. Unacceptable butterflies, on ce captured, were taste-rejected quickly, and most survived the sampli ng. The few presumably unacceptable butterflies consumed by the birds were not observed to cause vomiting. (2) After gaining some familiarit y with butterflies, young birds, like the adults, developed a reluctan ce to attack. They visually rejected certain classes of butterflies, o ften failing to attack them during an entire four-hour feeding trial. However, occasional attacks were made on butterflies in these 'rejecte d' classes. When this did occur, the insects proved to be actually eas ier to catch than those that were more often attacked. Once captured, however, the majority of these butterflies were taste-rejected. (3) Fo r a given butterfly species, most individuals were either consumed or rejected. Thus: each species could be clearly classified as either acc eptable or unacceptable to the jacamars. This consistency in jacamar r esponses resulted in a bimodal acceptability distribution of sympatric butterflies. (4) Young jacamars were capable of rapid associative lea rning and their responses were closely associated with butterfly visua l characteristics in which colour pattern, flight behaviour, and morph ology were also closely correlated. Thus, a single butterfly morpholog ical parameter termed body shape (body length/thoracic diameter ratio) can adequately predict the feeding responses of jacamars. Visually de tectable traits associated with butterflies possessing chemical defenc es may represent a balance between the need to signal unambiguously to specialized and/or experienced predators and the need to escape attac ks 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 an d behavioural characteristics between palatable and unpalatable butter flies in rainforest habitats.