ECOLOGY AND ENERGETICS OF SANDERLINGS MIGRATING TO 4 LATITUDES

We examined ecophysiological responses of Sanderlings (Calidris alba) to their nonbreeding environments in New Jersey (USA), Texas (USA), Punta Chame (Panama), and Puerto Viejo (Peru). Daily energy expenditure (DEE; measured using doubly labeled water) was strongly influenced by the thermal environment, being higher at colder locations, and equivalent to 4.2 times the basal metabolic rate in New Jersey, 2.8 in Texas, 2.1 in Panama, and 2.7 in Peru (200, 135, 100, and 129 kJ/d; n = 10, 5, 10, and 16, respectively). Time budgets varied among locations, but in all cases feeding and roosting accounted for approximately 90% of daylight hours. Feeding times were 55% in New Jersey, 90% in Texas, 40% in Panama, and 45% in Peru, suggesting that Sanderlings required more time to satisfy their food requirements in Texas than in the other locations. Total body mass and body fat increased linearly with decreasing long-term mean January air temperature but, because of the synchronous increase in energy expenditure, predicted survival times during food deprivation increased only slightly. Individual Sanderlings experience different living conditions throughout their non-breeding distribution, with DEE and nutritional reserves being determined primarily by temperature. Time budgets vary accordingly to accommodate these demands.