Northern Waterthrush - Evidence for Limited Habitat Availability on Wintering Grounds

Multiple Space-Use Strategies and Their Divergent Consequences in a Nonbreeding Migratory Bird (Parkesia noveboracensis)

Joseph A. M. Smith, Leonard R. Reitsma, Peter P. Marra

We investigated the relationships among space-use patterns, home-range attributes, and individual characteristics to determine the consequences of different space-use strategies for the overwinter physical condition of Northern Waterthrushes (Parkesia noveboracensis). We have elsewhere demonstrated that heterogeneity in food availability drives the movement decisions of site-persistent and itinerant individuals during the nonbreeding period. Here, we show that intraspecific competition played an important role in determining where individuals initially and eventually settled. Territoriality, characterized by aggression, sitepersistence, and exclusive home ranges, was more often found in males. Territorial birds gained mass over the winter, whereas birds that made midseason home-range shifts or that had home ranges with high intraspecific overlap tended to lose mass over the winter. The benefits associated with territoriality may be the result of maintaining higher-quality territories that were both wetter and had higher food availability than less exclusive home ranges. Our results suggest that despotism in the form of territoriality drives patterns of habitat occupancy, and in this system, high-quality habitat appears to be limiting for the Northern Waterthrush. This may have long-term consequences for the success of individual birds, because continued destruction of naturally limited habitats such as coastal mangroves, and predictions of a drying climate on wintering areas, have the potential to severely affect populations.