Feeding rates, search paths, and surveillance for predators in great-tailed grackle flocks

Abstract

Feeding rates, search paths, and surveillance behaviour of great-tailed grackles were measured to test the hypotheses that flocking influences: (a) feeding rates, (b) search behaviour, and (c) predator detection.Peck rates of grackles feeding on open grass meadows in Gatun, Panamá Canal Zone, did not vary with flock density and variation in peck rates was also independent of density. When grackles were in denser flocks, their search paths were straighter and, during the wet season only, they moved slower in denser flocks. Female grackles in denser flocks paused less often to scan the surrounding environment, presumably for potential danger.Although they were not strongly influenced by flocking, feeding and search behaviour of grackles was strongly affected by the sex of the grackles, the season, and the local feeding area. Grackle feeding behaviour hence seemed less closely adjusted to flocking than to other environmental factors.