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

This study was conducted in Lingshui, Hainan (18°29′ N, 110°4′ E). Located in the southeast of Hainan Island, Lingshui experiences a tropical monsoon climate with abundant sunshine and heat, and the terrain mainly comprises agricultural land (Liu and Liang 2021).Sparrows and Japanese tits are widely distributed across China including the tropical Hainan Island (Zheng 2023). At our study sites, sparrows and Japanese tits typically encounter various predators including sparrowhawks of the hawk family (Accipitridae) (Zheng 2023) as well as Pallas's squirrels (Callosciurus erythraeus) and maritime striped squirrels (Tamiops maritimus) of the squirrel family (Sciuridae) (Smith 2009).This study investigated whether alarm calls of Japanese tits (Parus minor) in response to different natural enemies 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 they show mobbing behaviors at variable intensities; 2) the response of sparrows to mobbing calls of Japanese tits seemed to be stronger than that of Japanese tits to conspecific mobbing calls, which was possibly due to flock size; 3) both sparrows and tits were more sensitive to alarm calls in response to chipmunks (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 influence 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.