Evidence of the impacts of global warming on the behaviour, phenology and demography of wild animal populations is accumulating. However, how high temperatures may affect animal cognition remains largely unknown. This is an important knowledge gap because cognition underpins behavioural flexibility, and it can be directly linked to fitness. We investigated whether high temperatures affect adult cognitive performance in the short term and long term in a wild population of southern pied babblers (Turdoides bicolor). We found that adults showed reduced cognitive performance with increasing air temperatures in the wild. Additionally, individuals that experienced higher mean daily maximum air temperatures as nestlings showed reduced cognitive performance as adults. Finally, individuals that experienced more days above 35.5 °C (a threshold associated with changes in foraging and provisioning behaviour in this species) as dependent fledglings had lower reproductive success as adults. These findings indicate that naturally occurring high temperatures can have both short- and long-term negative effects on cognition and reproductive success in wild bird populations, raising concerns for their ability to adjust to the changing climate.
