Annual diet of cedar waxwings based on U.S. biological survey records (1885-1950) compared to diet of American Robins: Contrasts in dietary patterns and natural history

Abstract

The diet of Cedar Waxwings (Bombycilla cedrorum) is described using records of gut contents collected by the U.S. Biological Survey. Cedar Waxwings eat more fruit than most other Temperate Zone birds, including one of the most frugivorous thrushes, the American Robin (Turdus migratorius; 84 vs. 57% fruit in their annual diets, respectively). Cedar Waxwings are almost exclusively frugivorous in the winter and early spring. During the spring period of fruit scarcity, flowers comprise a large portion of the diet of waxwings (44% of May diet). Cedar Waxwings eat aerial and vegetation-borne animal prey, whereas American Robins eat vegetation-borne and terrestrial prey. The fruits eaten by Cedar Waxwings are characterized by high sugar and low lipid content. American Robins, like other North American thrushes, eat sugary and lipid-rich fruits, suggesting contrasting digestive strategies in waxwings and thrushes. This perspective is reinforced by the correspondence between these birds' diets, the timing of breeding in relation to availability of preferred foods, and flocking patterns.