Estimation of Energy Flow in Bird Communities: A Population Bioenergetics Model

We describe a simulation model that estimates population density flux, biomass changes, and bioenergetic demands of bird populations, especially with reference to the breeding season. changes in the population density of adults of each species considered were calculated from breeding census values and information on migratory movements. Using field or literature values for clutch size, mortality rates, and reproductive phenology, we computed the population densities of the nestling, fledgling, and juvenile age classes of each species. Given information on adult body weights, weight changes of young were obtained from a logistic function, and the age class distributions within a population were used to estimate biomass changes in each age class through time. Coupled with an ambient temperature function, the bioenergetic formulations of Kendeigh, and considerations of the energy costs of digestion, activity, molt, egg production, and growth, this allowed an area—based estimation of the daily energy requirements of each age class of a population. When a community of several populations was considered, estimates for the total community as well as for each population were made. A sensitivity test of model constants and input variables suggests that output estimates may be most sensitive to variations in digestive efficiency, adult population density, the timing of arrival and departure, and ambient temperature. In general, however, the model appears to be fairly robust. We discuss examples of model output and uses of the model in theoretical and management investigations.