Sex-dependent elevational effects on bird feather moult

Environmental conditions, including weather, influence organisms in a variety of ways. Specifically, animal males and females might be affected differently by ambient temperatures that vary in time and space. In this study, we explored the effect of elevation, which strongly determines ambient temperatures, on the speed of moult of the wing’s flight feathers in the Eurasian Blackbird (Turdus merula). Differences in moult speed may alter the wing’s surface area during the moulting process and hence may influence flight performance, including the ability to escape from predators. Sampling elevations were categorized to locations > 1000 m above mean sea level (AMSL) and locations < 300 m AMSL. We found that birds moulted their primary wing feathers faster at low elevations than at high elevations. In addition, differences in elevation-related moult speed were modulated by bird sex. Males moulted their primary feathers faster than females at high elevations but slower than females at low elevations. Our findings highlight the importance of considering sex-dependent responses to spatial environmental conditions, which may influence key properties of major annual-cycle activities and life-history processes.