Snow cover constrains the behavioural flexibility of a winter-adapted bird

Behavioural flexibility is an important way in which animals respond to changing environmental conditions. During winter, snow cover is an important seasonal refuge that provides thermal insulation and protects overwintering species from predators. However, snow depth and quality can be highly variable throughout winter and it is unclear how species that use snow cover adjust their behaviour with changing winter conditions and in complex landscapes. During winter months, Ruffed Grouse Bonasa umbellus spend a large portion of time roosting in trees, understorey and, in some cases, subnivean environments. Importantly, the ability to roost under snow has been associated with reduced stress levels and increased overwinter survival. Across three winters, we studied plasticity of roosting behaviour across a diversity of winter conditions and land-cover types. In line with predictions, Grouse were more likely to use snow burrows when snow was deep and powdery, and experienced higher temperatures in snow roosts compared to other roost types. However, snow roosting behaviour did not vary strongly across land-cover types, and Grouse were not more likely to use snow burrows at lower temperatures, potentially because snow roosting may serve to protect them from predators regardless of winter weather conditions. Both the snow conditions necessary for snow roosting and the occurrence of snow roosting behaviour were relatively rare during our 3-year study (only 3% of all roosts were snow burrows). Loss of winter refugia due to warming winters and declining snow cover may limit the use of behavioural flexibility for winter-adapted species to cope with environmental change.