Prey Capture by the Brown Pelican

Abstract

METHODS of prey capture are of considerable interest to biologists. Fish-eating birds have been studied extensively (cf. Ashmole 1971) and, among seabirds, the order Pelecaniformes provides a diverse assemblage of capture methods. Owre (1967) describes in detail the structural adaptations for swimming underwater and impaling and seizing fish by the Anhingidae and Phalacrocoracidae respectively. The Fregatidae grasp their prey from very near the surface without entering the water (Wet-more 1965). The Sulidae and Phaethontidae plunge into the water and pursue fish and squid, probably to some depth. The white pelicans of the subgenera Pelecanus and Cyrtopelicanus seize their prey while swimming on the water surface, often fishing communally. The Brown Pelicans (Pelecanus occidentalis) however surface plunge for fish. The long bill and exaggerated gular pouch of pelicans have elicited speculation from biologists and laymen alike as to their actual movement underwater (Allen 1923, Coues 1927, Peterson 1963, Abbott 1966, Gardiner 1973). For the first time we are able to describe the use of the bill and pouch during prey capture by diving Brown Pelicans. Fig. 1 is a composite made from 35-mm color slides of pelicans diving in various situations in Florida. Figs. 2 and 3 are selected composites of slides obtained with a motorized Nikon held approximately 2 feet underwater while baiting the nearby pelicans with frozen fish in front of the camera. While these photographs were obtained under somewhat unnatural conditions at a marina in the Florida keys, we believe they accurately represent the technique Brown Pelicans use when diving to catch live fish. Considerable variation exists in the aerial diving process, probably accountable through interactions of several factors: individual experience of the birds; the species, size, depth, speed of movement, and schooling 649 The Auk 92: 649-654. October 1975