High temperatures inhibit quantity discrimination of conspecifics in a wild bird

Abstract Temperatures globally are increasing, resulting in numerous behavioral consequences for wildlife. Mobbing, a collective antipredator response important for many species, is one such behavior affected by high temperatures. Recent research has shown the number of individuals involved in a mobbing event to be an important determinant of whether individuals join in, suggesting a role for numerical abilities in this behavior. However, whether temperature affects an animal's ability to discern the number of conspecifics involved in a mobbing event has not yet been investigated. Temperature-induced cognitive declines may affect the processing and decision making involved in the anti-predator response, potentially leading to maladaptive anti-predator behaviors. We presented wild great tits (Parus major) with playback of the mobbing calls of 1 or 5 conspecifics at different temperatures (from 16 to 35 °C; representing temperatures both within and outside of the thermoneutral zone [15 to 30 °C] of this species), to determine if temperature affected their mobbing response. We found a quadratic relationship between temperature and the number of mobbing calls produced by great tits, with the number of calls produced by individuals decreasing at higher temperatures, regardless of playback treatment. Importantly, while great tits showed a stronger approach response to 5 compared with 1 caller at low temperatures, they failed to do so at higher temperatures, either due to an impaired ability to discern the number of mobbing individuals, or an altered thermoregulation-predation risk trade-off at these high temperatures. Inappropriate anti-predator responses in the heat are likely to have substantial effects on survival, particularly as temperatures continue to rise.