Intraspecific Kleptoparasitism and Foraging Efficiency as Constraints on Food Selectin by Kelp Gulls Larus Dominicanus

Abstract

Kleptoparasitism (food-stealing) is widespread among birds and is an important feeding technique of some families of seabirds, notably Fregatidae (frigatebirds), Chionididae (sheathbills), Stercoraridae (skuas) and Laridae (gulls and terns), being reported for more than 25% of species within these families (Brockmann and Barnard 1979). A useful axis along which to divide the behaviour between species is a ‘specialist-opportunist’ continuum. No seabird species is known to be an obligate kleptoparasite, but specialists, such as skuas and frigatebirds, obtain a large proportion of their food by kleptoparasitism of heterospecifics. It has been suggested that they may possess structural adaptations associated with these feeding techniques (Brockmann and Barnard 1979), although the evidence for this is weak (Furness 1987). All kleptoparasitic species steal food from other species, but several opportunistic kleptoparasites, such as gulls and terns, also practise this behaviour intraspecifically (e. g. Hopkins and Wiley 1972; Hulsman 1976; Verbeek 1977a,b; Rockwell 1982; Greig et al 1983; Hockey et al. in press). In a recent review, Furness (1987) concluded that such opportunistic kleptoparasites were as successful at stealing food as were specialist kleptoparasites.