Effect of dietary lipid level on lipid passage rate and lipid absorption efficiency in American robins (Turdus migratorius)

Thrushes consume a variety of fruit that differ greatly in nutrient composi tion, especially Lipid content. Thrushes may be efficient at extracting ene rgy from fruit diets by changing how they digest meals differing in lipid c ontent. We tested for this capability in American robins (Turdus migratoriu s) by acclimating them to diets differing in Lipid content and measuring pa ssage rate and absorption efficiency of ingested Lipids with radiolabeled m arkers. Birds acclimated to high-lipid (26% and 40% dwt) diets ingested les s dry matter and retained ingested lipids in their gastrointestinal tract t hree times longer than when acclimated to a low-lipid (9%) diet. Absorption efficiency did not differ among diets (similar to 74%), suggesting robins minimize feeding time rather than maximize rate of energy gain when process ing meals. Thus, robins slowed intake and passage rate of dietary Lipids wi th increasing dietary Lipid concentration while maintaining a steady Lipid absorption efficiency. J. Exp. Zool. 283:408-417, 1999. (C) 1999 Wiley-Liss , Inc.