The role of alarm responses in the formation of mixed-species flocks of heathland birds

Summary Birds of ten species with similar short flight distances from a human intruder associated with stonechats (Saxicola torquata), which have large flight and alarm call distances. The attendants probably took advantage of the domain of safety around the stonechat, produced by the difference in flight distance. Stonechats have no reciprocal advantage, and were not seen to initiate flocks.Flocks were formed with both calling and silent stonechats. Benefits in the latter case probably include early warning of danger, but there may also have been a reduction in vigilance by attendants.The relative flocking activity of attendant species (number of associations observed; percentage of incidents with silent stonechats; rate of warning calls by stonechats joined) was related to the species' average flight distance from an intruder (Fig. 1). Possible explanations are consistent with a correspondence between flocking tendency and the degree of benefit obtained.