Effects of Food Type and Patch Location on Foraging in Local Birds: A Field Test of Optimal Foraging Predictions

Abstract

Optimal foraging theory predicts that a foraging organism will maximize its fitness by maximizing its net energy intake per unit time, and will usually choose the available food type that yields the most calories for the effort it takes to locate, catch, or consume it. In an environment in which food is distributed in patches across different habitat types, foragers must decide which patch to visit and how long to forage there. These decisions can become complicated when competing foragers or predators are present. In this study, I compared the duration of visits of four species of overwintering passerines between bird feeders containing hulled and unhulled sunflower seeds, and also between feeders set up under forest cover and in an open field. Birds spent more time at feeders containing hulled sunflower seeds, which had a lower handling time, than at feeders containing unhulled seeds. They spent no more time at feeders in the forest than at feeders in the open, but did show a larger marginal preference for hulled seeds in the open habitat.