Winter mortality of a passerine bird increases following hotter summers and during winters with higher maximum temperatures

Climate change may influence animal population dynamics through reproduction and mortality. However, attributing changes in mortality to specific climate variables is challenging because the exact time of death is usually unknown in the wild. Here, we investigated climate effects on adult mortality in Australian superb fairy-wrens (Malurus cyaneus). Over a 27-year period, mortality outside the breeding season nearly doubled. This nonbreeding season mortality increased with lower minimum (night-time) and higher maximum (day-time) winter temperatures and with higher summer heat wave intensity. Fine-scale analysis showed that higher mortality in a given week was associated with higher maxima 2 weeks prior and lower minima in the current fortnight, indicating costs of temperature drops. Increases in summer heat waves and in winter maximum temperatures collectively explained 62.6% of the increase in mortality over the study period. Our results suggest that warming climate in both summer and winter can adversely affect survival, with potentially substantial population consequences.

Automated summary

Climate change can affect animal population dynamics by influencing reproduction and mortality. This study found that adult mortality in Australian superb fairy-wrens increased during the nonbreeding season and was associated with lower minimum winter temperatures, higher maximum winter temperatures, and higher summer heat wave intensity. Increases in summer heat waves and winter maximum temperatures accounted for 62.6% of the overall increase in mortality observed over a 27-year period. These findings suggest that climate warming in both summer and winter can have detrimental effects on survival and potentially significant population consequences.