Eavesdropping alarm calls of Japanese tits (Parus minor) by Eurasian tree sparrows (Passer montanus)

Mobbing is an important anti-predation strategy that can warn other potential prey, communicate predator threats and reduce predation risk. Previous studies examined how animals transmit and receive information and investigated their cognitive abilities; however, the potential effects of other ecological factors were rarely considered. This study investigated whether alarm calls of Japanese tits (Parus minor) in response to different predators would affect the responses of Eurasian tree sparrows (Passer montanus). The results indicated that: (1) sparrows differentiated heterospecific alarm calls and the level of danger from natural enemies conveyed in these calls, and the recruitment of sparrows by the alarm calls to chipmunks [11.5 ± 12.1, mean ± standard deviation (SD), n = 24] was significantly higher than sparrowhawks (2.43 ± 3.61, n = 21; Wilcoxon rank sum test, P n = 23; Wilcoxon rank sum test, P Tamias sibiricus) than sparrowhawks (Accipiter nisus), which suggested chipmunks were the main predator. Hence, besides natural enemies affecting the sparrows’ responses to heterospecific mobbing calls, flock size also influences this behavioral response. We suggest that future studies consider the effects of multiple ecological factors on the perception of heterospecific mobbing calls to accurately interpret mobbing call responses and thus better reveal the mechanisms associated with encoding, transmission, and perception of information among animals.