Fruit Choice in Neotropical Birds: The Effect of Distance Between Fruits on Preference Patterns

The influence of distance between fruiting plants on choice patterns of four species of tanagers and two species of manakins was experimentally tested in a lowland rain forest in Costa Rica. Paired clusters of two fruit species (Miconia affinis and Urera caracasana) were presented on each of two perches separated by selected distances ranging from 0.3 to 6.4. When the two perches were closest together, all the birds ate the preferred berries, M. affinis, on both perches before eating the less preferred U. caracasana. At the extreme perch separation distance, all but one of the birds ate both species of fruits on the first perch before flying to the second perch. The distance at which each bird switched between the two feeding sequences was correlated with the strength of their preference for one species of fruit over another. Manakins switched at greater separation distances than did tanagers. Since manakins take most of their fruit on the wing, the difference in switch distance is likely related to their flight pattern, but no consistent correlation with simple morphological characteristics (wing—loading or aspect ratio) was found. The results suggest that, in the field, less preferred items may often be taken when more preferred fruits are spaced even moderately far apart. The sequence of feeding and, by implication, diet breadth appears to be a consequence of the abundance and spacing of available foods; hence, degree of generalization is a dynamic feature of a bird's foraging pattern. This result supports the prediction that travelling time is an important determinant of prey and patch choice.