Tannin and Protein in the Diet of a Food-Hoarding Granivore, the Western Scrub-Jay

Abstract

Plant tannins are known to impede vertebrate protein digestion. The severity of their impact on vertebrates, particularly birds, may be a function of the relative presence of lipids and proteins (or individual amino acids) in the diet. We examined the effects on six captive Western Scrub-Jays (Aphelocoma californica) of dietary lipids and proteins in artificial diets that varied in tannin activity. Tannin variation in the artificial diets was within the range of concentrations in Gambel oak (Quercus gambelii) acorns, an important winter food. Jays lost mass on low-protein diets and lost the most mass on low-protein, high-tannin diets. A significant protein-tannin interaction existed such that tannin effects were eliminated in high-protein diets. No significant changes in weight were associated with any lipid treatments.