Decomposition of Nitrogenous Compounds by Intestinal Bacteria in Hummingbirds

Abstract

Degradation of urinary nitrogen-containing compounds by bacteria in the ceca of birds occurs in a number of herbivorous and omnivorous species, and cecal absorption of the products of that degradation has been reported in chickens. This recycling of nitrogen may play an important role in nitrogen balance, especially in those species with low dietary nitrogen intake. We report, for the first time, degradation of nitrogenous compounds by intestinal bacteria in a bird that is nectarivorous and lacks ceca, Anna's Hummingbird (Calypte anna). Hummingbirds subsist year-round on a liquid diet with an exceptionally low-nitrogen content. Ureteral urine containing ammonia, urea, and uric acid has been observed in the lower intestinal tract of Anna's Hummingbird. Bacteria obtained from intestinal contents and homogenates of the anterior and posterior intestine of this species were able to break down uric acid, urea, and potassium urate, but not sodium urate. This degradation is the necessary first step in the recycling of nitrogen. Assessing its significance will involve determining whether the products of microbial breakdown are subsequently absorbed across the intestinal walls of these unique animals.