Fruit Choices by Captive American Robins

Individual variation in fruit choice by captive American Robins (Turdus migratorius) was marked, for most of the tested fruit traits (color, nutrient content, seed load), and choices were often contingent on other factors. Robins often favored blue, and sometimes red, artificial fruits over green or yellow ones, although one bird preferred green and rejected blue. Color preference rankings were usually transitive but did not closely correspond with the frequency ranks of fruit colors in nature. Choice tests with naturally occurring polymorphic fruits showed that both color morphs seemed to be palatable and that the robins' preferences did not necessarily reflect the natural frequency of the color morphs. Robins often selected high-lipid and high-glucose fruits when dark in color, but not when the higher nutrient level was a lighter shade of the same color. Slight decreases of accessibility often altered the preference rankings. Robins did not prefer fruits with low seed loads (high pulp/seed ratios). Robins may provide more consistent selection for certain fruit traits, such as color, than several other species previously examined. However, considerable individual variation was evident, and evidence for selection on macronutrient level was mixed.