Feeding Ecology and Prey Selection in the White Ibis

Abstract

Prey selection is constrained by a predator's behavior and morphology and by the availability of suitable prey. Although a number of investigators (Tinbergen 1960, Ivlev 1961, Gibb 1962, Holling 1965, and Royama 1970) have studied predation tactics and have developed hypotheses to account for their empirical data, much remains to be learned about the relationship between the availability of prey in natural systems and its consumption by predators. Particularly important is the question of how prey availability influences prey consumption within the areal range of foraging patches used by a predator. Differences in density, type, distribution and quality of prey may all influence what a predator consumes. This question becomes most interesting, and most difficult to resolve, in mobile, wide-ranging animals such as large birds, whose selection of prey may be expected to vary from habitat to habitat within a region. In this paper, I examine prey selection of the White Ibis (Eudocimus albus), a wideranging wading bird. I have attempted to determine the energetic relationships of prey selection on a region-wide basis in order to elucidate the tactics used by such a species in meeting its annual energy requirements. Most work on predation ecology has concerned visually-foraging predators. However, many predators, such as the White Ibis, are tactile, nonvisual foragers (Kushlan 1978a) and are limited in their ability to choose among potential prey. Such choice is required by most theoretical considerations of predation. Nonvisual foraging behavior should affect patterns of prey selection and may differ in crucial detail from better-understood visual techniques. In this study I examine those differences.