Communal roosting is often a regional phenomenon that involves wide-ranging and long-lasting relationships among associations. We examined roosting behavior on a scale sufficiently large to detect regional and seasonal patterns. For five roosting seasons (June-November), we studied the population dynamics of all roosting flocks of European Starlings (Sturnus vulgaris) and Common Grackles (Quiscalus quiscula) located within a l,OOO-km2 census area in central New Jersey. Roosts were active from 3-20 weeks and ranged in size from 2,000 to over 100,000 individuals. The total roosting population (TRP) in "major" (>2,000 birds) flocks increased through early summer, generally achieving maximum size in mid-August when the largest number of roosts was active. When TRP was largest, size of major roosts varied greatly (range 2,000-100,000 individuals). Through late summer and early fall, size and number of major roosts and TRP declined. By late fall few major roosts were active, but those remaining were large (> 30,000). Movements of individual birds (radio-tagged) suggested that changes in size of TRP resulted largely from exchange of the local population between small, "minor" roosts (largely undetected and not included in roost censuses) and major flocks. Current hypotheses concerning the functional basis of communal roosting do not adequately explain patterns of roosting behavior that we observed. BRENNER, F. J. 1965. Metabolism and survival time of grouped starlings at various temperatures. Wilson Bull.
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