The Complex Relationship Between High Temperatures and Avian Breeding Success: Insights From a Global Review.

Climate change is one of the major threats to biodiversity. Understanding how species cope with increasing temperature is of prime importance when assessing population viability. We present a systematic review of the association between high temperature and the breeding success of wild birds. We focus on avian species, as they are widespread throughout the world and benefit from numerous long-term monitoring programs. We conducted a survey in the Web of Science library and retained 229 studies based on our eligibility criteria. We qualitatively assessed whether studies investigated the effect of high temperatures. High temperatures were defined in regard to the average temperature recorded at the study site. The species thermoregulation was taken into account depending on the information available. We were able to extract the local climate type (i.e., arid, temperate, continental, polar, and tropical) for 135 studies. Temperate and continental climates were over-represented, and studies were more likely to investigate the relationship between hot events and breeding success in arid environments. The relationship between high temperatures and breeding success is highly complex, as it most likely involves a combination of "direct" effects (mediated through thermoregulation) and "indirect" effects (mediated through phenology, food availability, trophic interactions) and may vary depending on the system studied. Finally, we present some considerations for future studies, in particular regarding species' sensitivity at high temperatures.