Stress‐induced variation in protein utilization and plasma glucose in a male passerine bird from urban and rural populations

In mammals, stress increases the secretion of glucocorticoids, resulting in the mobilization of energy substrates such as glucose. We investigated the mobilization of glucose and proteins in a wild‐caught male passerine, the Abert's Towhee, Papilo aberti , in response to mild acute stress. Birds were captured from urban and rural populations and blood samples were collected immediately after capture and 60 minutes later (after handling and mild restraint‐induced acute stress). Birds were then transported to the laboratory where they were allowed to acclimate for 12–38 days prior to collecting another blood sample. Plasma glucose (P Glu ) did not increase in response to acute stress, but significantly increased by 11.8% and 5.5% in urban and rural birds, respectively, after birds were brought into captivity. This increase may be related to the ad libitum availability of high quality food. No further changes in P Glu were observed over the following 38 days. Plasma uric acid significantly decreased by 34.1% in birds from urban locations and 51.7% in birds from rural locations in response to acute stress, suggesting decreased protein utilization in both populations. Neither P Glu nor plasma uric acid differed between birds originating from urban and rural populations. Ongoing studies are aimed at measuring plasma glycogen to determine if glycogenolysis contributes to the captivity‐associated increase in P Glu .