ROOSTING AND DIURNAL MOVEMENTS OF RADIO-TAGGED AMERICAN CROWS

Cooperatively breeding birds characteristically defend territories in which they forage and roost all year. In contrast, the cooperatively breeding American Crow (Corvus brachyrhynchos) is notorious for large feeding and roosting aggregations during the non-breeding season. These observations suggest a pattern of fidelity to diurnal activity centers (DAC's) with daily movements to roosts and areas of superabundant food, much like the movements of communally roosting blackbirds and starlings. We radio tagged and color marked crows at a farm in central New Jersey to examine roost use and fidelity to territories during the winter. Birds exhibited two distinct movement patterns. Seven of 11 crows returned to the farm daily where they maintained stable territories in groups of 4-5. These "DAC-based" crows left the farm early in the afternoon and travelled to large communal roosts 14-18 km from the farm. The largest roost (> 5000 crows) was 4.5 km from a landfill where thousands of crows fed daily. DAC-based birds sometimes stopped at landfills in transit to roosts. Although they were almost always together at the farm, crows from the same group usually did not travel together or make the same stops between the farm and the roost. In contrast to DAC-based crows, the other birds rarely returned to the farm and were difficult to find during the day. These "vagrant" crows were most often found at landfills and probably were not part of stable groups, although they used the same roosts as DAC-based birds. Vagrants disappeared during the middle of the winter, suggesting that they were not permanent residents in the study area.