Understanding bird migration by combining telemetry data with an individual-based model

We present an individual-based model of the northward, spring migration of Western Sandpipers (Calidris mauri). The model simulates daily movements of birds between stopover sites along the Pacific coast of North America to their Alaskan breeding grounds. At each site, food or energy intake is influenced by the density of other birds at the stopover site; mortality due to predation is influenced by both numbers of conspecifics at the site and by individual fuel stores of the migrating birds; and flight distance is affected by wind conditions and individual fuel stores. Movement between sites and stopover behavior is controlled by individual decision rules. We use optimization of arrival time and fuel levels at arrival to find behavioral rules. Western sandpipers have been tracked during spring migration for several years by attaching radio transmitters to birds. We use likelihood analysis to compare the migration patterns of model birds to the data and ask how well behavior generated by optimization produces matches the observations.