Influence of Moisture and Food Supply on the Movement Dynamics of a Nonbreeding Migratory Bird (Parkesia noveboracensis) in a Seasonal Landscape

Abstract

We radiotracked Northern Waterthrushes (Parkesia noveboracensis) in four habitats in Puerto Rico during two winters (i.e., January–April) in 2003 and 2004 to determine the ecological determinants of diurnal space use and overwinter sitepersistence in this species. The majority of birds (69%) were sedentary and used a contiguous area within a single habitat over the winter period. A smaller percentage (31%) initially used a contiguous area within a single habitat but then permanently moved from that area to another disjunct location (mean = 418 m). Most of these movements were out of the two habitats (dry forest and Black Mangrove) that became the driest from January to mid-March and into wetter mangrove areas. The primary determinants of movement probability were moisture and food availability on each bird's home range. Foraging areas of birds that eventually moved were drier and had lower food availability than areas used by site-persistent individuals. The sites that these itinerant birds moved to were wetter and had higher food availability, which suggests that individuals moved in response to changing resources. Our results (1) indicate that habitats used by this species differ in suitability and (2) support previous findings that turnover rates within a habitat could serve as an indicator of habitat quality. The ability to predict behavioral responses of individuals to habitat conditions that vary across space and time is essential for understanding individual and population responses to habitat loss and the effects of a changing climate in the New World tropics.