MAXIMUM ENERGY-INTAKE RATE IS PROPORTIONAL TO BASAL METABOLIC-RATE INPASSERINE BIRDS

A high energy intake rate may be important for many animals, but littl e is known of factors that determine intake capacity. Birds in migrato ry disposition presumably eat at their maximum capacity and therefore form a good model for studying the energy intake capacity of animals. We measured the maximum daily energy intake (GEI(max)) and basal metab olic rates (BMR) in 22 species of migrant passerines during autumn. Bo th GEI(max) and BMR scaled to body mass (W) close to W-0.70. More impo rtantly, species with high GEI(max) for their body mass also had relat ively high BMR. BMR may reflect the size of the metabolic machinery in volved in energy uptake. The maximum daily metabolizable energy intake (DME(max)) was estimated from our GEI(max) data. The average ratio DM E(max)/BMR was 4.6. In comparison, daily energy expenditure of reprodu cing passerines have been reported in the literature to be 3.6 times B MR. This suggests that energy intake rates may not normally limit bree ding performance in passerines. Earlier studies have shown that BMR of homoeotherms reflect the rate of energy expenditure during reproducti on. Our study shows that the energy intake capacity also correlates wi th BMR, which gives new perspectives on the ecological significance of BMR.