This project continues studies of mixed-species flocking in birds wintering in temperate-deciduous forest and concerns the use of the newly-discovered technique of "ptilochronology". Ptilochronology indexes the degree of energy stress on a day-by- day basis by measuring the rate of growth of a feather replacing one that has been intentionally plucked. For birds during the non-breeding season, the rate of feather growth is related to net energy intake, and can be used to monitor energy stress, the culmination of which is death. The rate of feather growth can be viewed as a sensitive indicator of the risk of starvation and, therefore, can be treated as a direct measure of the adaptiveness of behavior. Ptilochronology will be used to assess the degree of energy stress experienced by birds foraging in conspecific and heterospecific flocks of controlled composition. The technique holds promise for answering many other fundamental questions in avian ecology.//
