SIMULATED BEHAVIORAL ENERGETICS OF NONBREEDING AMERICAN ROBINS - THE INFLUENCE OF FORAGING TIME, INTAKE RATE AND FLYING TIME ON WEIGHT DYNAMICS

We describe the development of a simple model representing individual energetic and time budget activities of a nonbreeding American robin ( Turdus migratorius). In the model, values for energetic costs and phys ical activity were derived from various literature sources, and are in fluenced by the proportion of time spent in each activity, time of day , and bird weight. We used multiple combinations of intake rates, fora ging times and activity budgets to simulate weight dynamics. In our si mulations, a robin had to forage between 21-50% of daylight hours mere ly to maintain its weight, far more than some studies predict. A robin gained weight by increasing time spent foraging, increasing food inta ke rates or decreasing flight activity. This model can be a useful too l in exploring the effects of various combinations of behavioral and e nergetic activities on robin weight. It can also serve as a baseline f or future analyses involving the influence of various human activities in American robin behavior and weight dynamics. (C) 1998 Elsevier Sci ence B.V. All rights reserved.