Seasonal Differences in Community-level Mobbing Responses of Passerines Toward a Diurnal Owl in Taiwan

Prey use a variety of anti-predator behavior, including alarm calling and approaching predators, and may adjust these behaviors by evaluating their benefits and costs. However, it remains unclear how prey expresses anti-predator behavior across seasons, when both breeding status or predator diet may influence perceived risk. We conducted nine-minute playback surveys (six-minute quiet period and subsequent three-minute playback) using calls of Collared Owlet (Glaucidium brodiei), a diurnal owl that preys on passerines, at 93 sites during breeding season and non-breeding season in Taiwan. We quantified whether the small passerine birds approach and make alarm call or not to quantify mobbing response. We found that probability of making alarm calls did not differ between seasons (30.88% and 29.15% in breeding and non-breeding season, respectively), whereas probability of approaching was higher in breeding (25.63%) than in non-breeding season (13.28%). To verify that responses were specific to predator cues rather than to loud vocalizations in general, we conducted supplementary playbacks using calls of a non-predatory species, Taiwan Barbet (Psilopogon nuchalis), which elicited markedly lower mobbing responses. Together, these results indicate that small passerine birds mob in both seasons but reduce the use of higher-risk behaviors against predators during the non-breeding season, consistent with seasonal variation in predation risk.