INFLUENCE OF FORAGING AND ROOSTING BEHAVIOR ON HOME-RANGE SIZE AND MOVEMENT PATTERNS OF SAVANNAH SPARROWS WINTERING IN SOUTH TEXAS

We used radio telemetry to examine Savannah Sparrow (Passerculus sandwichensis) homerange size and foraging and roosting behavior on Padre Island National Seashore in south Texas during January and February, 2002 and 2003. Savannah Sparrows maintained fixed home ranges in winter. Mean home-range size (95% Kernel Home Range [KHR]) was 9.1 ha with a mean core area (50% KHR) of 0.9 ha. Within home ranges, mean foraging and roosting areas were 5.6 and 6.6 ha, respectively. Three distinct habitat types were used by Savannah Sparrows on the island: foredunes (adjacent to the ocean), interior grasslands, and lagoons. Birds using the foredunes had significantly larger home ranges and traveled longer distances between their foraging and roosting locations, always moving inland to roost. Roosting and foraging areas overlapped less for these birds (20%) compared with the overlap for birds found in interior grasslands (45%) and lagoons (55%). The greater distance traveled to roost sites by birds foraging in the foredune habitat appeared to be related to increased exposure in that habitat type. Savannah Sparrows selected foraging areas with less vegetative biomass and more bare ground than random sites. Roost sites had greater total (live) cover than foraging and random sites. Savannah Sparrows foraged alone or in loose aggregations with conspecifics. Birds roosted alone or in aggregations of up to 30 individuals. Savannah Sparrows often roost outside of their foraging areas; this study draws attention to differences in space use for roosting and foraging Savannah Sparrows. Although Savannah Sparrows maintained relatively small home ranges, they occasionally moved at larger spatial scales, suggesting a need for intact grassland patches much larger than the average home-range size. [PUBLICATION ABSTRACT]