Effects of substrate on prey use by belted kingfishers (Ceryle alcyon): a test of the prey abundance – availability assumption

Abstract

Foraging trials were conducted using belted kingfishers (Ceryle alcyon) to examine relationships among prey abundance, availability, and use. Because these relationships are affected by the preference of the predator, I also determined the prey preference of belted kingfishers. Fish (Pimephales promelas and Catostomus commersoni) and crayfish (Orconectes spp.) were exposed to predation by 12 wild belted kingfishers under 4 treatments in which prey availability was manipulated by altering habitat structure. The preferred prey of belted kingfishers were relatively large fish (11–13 cm long). In structurally simple habitats, prey use by belted kingfishers reflected this preference. Complex habitat structure reduced the availability of preferred prey items and resulted in prey use that did not differ from the initial prey abundance distribution. These experiments demonstrated that prey abundance was not equivalent to availability and that habitat structure and prey preference had important effects on the relationships among prey abundance, availability, and use. Thus, evaluating the importance of prey resources to predators on the basis of prey abundance–use comparisons, while ignoring prey availability and the dynamic factors that influence it, may lead to erroneous conclusions.