Laboratory Studies of Foraging in Four Bird Species of Deciduous Woodland

In an indoor aviary containing 60 American elm branches of 6 different diameters (0.5, 1.0, 2.5, 5.0,10.0,20.0 cm), Carolina Chickadees, Tufted Titmice, male and female Whitebreasted Nuthatches, and male and female Downy Woodpeckers were allowed to forage singly under controlled circumstances.Each species had a particular and unique preference for branch size and branch surface.Variation occurred among the individuals of each species or sex, and differences between the sexes were found in branch sizes used by woodpeckers and branch surfaces selected by woodpeckers and nuthatches.Nuthatches alone seemed partially to select branch size by total available surface area; they also showed the greatest diversity in use of the three branch surfaces (top, sides, bottom).Differences among species in their use of different branch sizes and surfaces and in the extent to which their behavior changed with experience generally supported Morse's (1974) hypothesis that socially subordinate species are behaviorally more plastic in thief foraging and occupy a broader fundamental niche.