The influence of morphology on fruit choice in neotropical birds

Abstract

The morphology of fruit-eating birds has a strong and complex influence on their selection of fruits. Through a series of aviary experiments, we examined the fruit-selection behavior of frugivorous birds. Among the species we tested, there were two fairly distinct groups, separated on the basis of their morphology and foraging behavior. One group, which includes the Cotingidae, Pipridae, Trogonidae, and Tyrannidae, have fairly short, broad wings, a wide gape with a short, flat bill and comparatively little leg musculature. The second group (e.g., Rhamphastidae, Emberizinae, Thraupinae) are characterized by longer, deeper bills and stronger legs. These differences in morphology are correlated with how the birds feed and thus, their selection of fruits. Fruit placement, for example, is differentially important to the two groups. Birds of the first group will readily fly for fruits that are difficult to reach from a sturdy perch whereas birds of the second group rarely do so, preferring to reach. Flying for fruits requires a greater energy expenditure than reaching; birds of the first group display a correspondingly higher selectivity of fruits than members of the second group whose low-cost reaching apparently allows them to include lower quality items in their diets.