Alternative strategies of space use and response to resource change in a wintering migrant songbird

The causes and consequences of nonbreeding space-use strategies are poorly understood. We studied 2 alternatives, sedentary and floating behaviors, in a wintering population of the Ovenbird (Seiurus aurocapilla), a Neotropical--Nearctic migrant, in response to manipulated and natural variation in food availability over 4 years in Jamaica, West Indies. Using radio transmitters, we documented in sedentary individuals use of a fixed home range, greatly overlapping those of neighbors, as well as core areas that overlapped little, suggesting that Ovenbirds defend the core of their home range as a territory. Floaters included individuals with multiple disjoined home ranges and individuals that undertook frequent excursions, but floaters always occupied relatively large feeding areas. Floaters comprised 8--17% of the population, and in some individuals, the behavior persisted in multiple winters, but the behaviors were not sex or age restricted. Sedentary birds were attracted to artificial feeding stations located within their home range. However, reduction of food availability did not induce sedentary individuals to expand or shift their home range or to adopt floater behaviors. By contrast, floaters appeared better able to exploit seasonal or experimentally induced variation in food availability by matching their space use to the resources. The physical consequences of these alternative wintering strategies were situation dependent: Whereas body mass of territorial birds was positively correlated with food availability, floaters showed the opposite response, with higher mass in food-reduced situations. These results suggest that alternative behaviors represent a trade-off in response to resource availability. Copyright 2008, Oxford University Press.