Seasonal Patterns in Roosting Flocks of Starlings and Common Grackles

Abstract

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.

Heritable basis for choice of group size in a colonial bird

“…Variation in group size has been observed in foraging groups, leks, extended family groups, migratory herds and flocks, communal roosts, and breeding colonies (1)(2)(3)(4)(5)(6)(7)(8)(9). This natural variation in group size has been used to measure consequences of sociality, such as reproductive or foraging success and predator avoidance through vigilance, and to infer the selective advantages of grouping (10)(11)(12)(13)(14)(15)(16).…”

Distribution Pattern and Characteristics of Grey Starling Sturnus cineraceus Summer Roosts in the Eastern Kanto Area

“…DAVIS (1970) found that European Starlings abandoned summer roosts in October; he related the change in flock size with gonadal change in the starlings. CACCAMISE et al (1983) also observed the abandonment of many summer roosts of European Starlings in autumn.…”

Bird use of grain fields and implications for habitat management at airports

“…Red-winged blackbird flocks can shift from small groups of breeding birds in summer to million plus winter communal roosts with other species (Yasukawa and Searcy, 1995). Communal roosts of starlings and common grackles peak from June to November, often exceeding 2000 birds (Caccamise et al, 1983). From these communal centers, starlings have been observed dispersing up to 50 miles to foraging areas such as row crop fields (Hamilton Iii and Gilbert, 1969) and even establish diurnal activity centers (Morrison and Caccamise, 1990).…”