Foraging habitat selection by American and Magellanic oystercatchers (Haematopus palliatus and H. leucopodus) on Patagonian tidal flats

Abstract

I examined the foraging behaviour of American and Magellanic oystercatchers on Patagonian tidal flats in the context of several abiotic and social factors. I analyzed the simultaneous effect of tidal state, wind speed, temperature, habitat preference, and species abundance of one species on the other by means of multiway contingency tables and loglinear models. Diets of both species were similar and reflected the natural abundances of prey items in the tidal flats. Both species were strongly influenced by tidal state when selecting foraging habitat, but other factors modified their preferences. I found that the foraging behavior of American Oystercatchers was determined solely by abiotic factors; i.e., tidal state, foraging period, and a higher order interaction effect between wind speed and tidal state. By contrast, no combination of abiotic factors was sufficient to explain the observed abundances of Magellanic Oystercatchers. Instead, their foraging behavior was facilitated by the presence of congeners in addition to abiotic factors.