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Many butterflies in tropical forests feed on fruits that have fallen to the forest floor. This substrate differs in many ways from floral nectar, and therefore fruit-feeding butterflies are expected to possess adaptations for efficient foraging, choice, and ingestion of their food. Differences in food quality and in spatial and temporal availability are also likely to have led to life history evolution. Here we describe the sugar and nitrogen content of fruits that butterflies feed on in at ropical forest in Uganda, and measure the attractiveness of these fruits to the local butterfly fauna together with the role that decay plays in the attraction. These data are supplemented with feeding observations at fruit falls in the forest. Our results show that (1) fruits contain significant and variable concentrations of sugar and nitrogen, and constitute a nutritious food source for butterflies in tropical forests; (2) fruit-feeding butterflies use cues from the fruits and fermentation products to locate their food; (3) different classes of fruit-feeding butterflies may vary in their preferences for certain fruits, and differ in their ability to find preferred food; an d( 4) fruit choice is not strongly correlated with attractiveness or nutrient content. The results are discussed in the light of the evolution of food searching and life history strategies.

Adult butterflies feed from a variety of substrates and have appropriate adaptations. We examined proboscis morphology in a community of fruit-feeding butterflies (Nymphalidae) in a tropical forest in Uganda. These data were supplemented with behavioural observations and measurements of intake rate on natural and artificial substrates. We found no sexual dimorphism in proboscis morphology even though puddling behaviour is usually performed by males. Two main feeding techniques could be distinguished on the basis of behaviour and morphology: the piercing technique, typically found in Charaxinae, and the sweeping technique employed by both Nymphalinae and Satyrinae. These techniques, distinguished in previous studies, are described in more detail and their relative efficiencies are discussed in the context of sexual dimorphism, food-choice and life history evolution. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86, 333–343.