Mountain Hares Are Adapted to Historical Climates—Coat Colour Mismatch is Greatest in Areas With the Largest Reduction in Snow Cover Duration Over the Last 60 Years

Climate change has reduced the duration of seasonal snow cover in many areas, leading to seasonal coat colour-changing species being colour mismatched against their environment for increasingly long periods. This mismatch in camouflage can lead to increased predation, potentially resulting in population-level effects. Here we investigate how mountain hare (Lepus timidus) camouflage is influenced by climate change-induced reductions in snow cover over a 60-year period. We quantified the degree of camouflage mismatch using multiannual (2011-2018) camera trap data from 678 camera traps spread across an environmental gradient in Norway spanning from 58° N to 69° N, and from coastal to inland areas. We coupled this camouflage data with a 60-year snow cover time series on a national scale, creating two 30-year averages of snow cover duration (1959-1988 and 1989-2018). We investigated how climate change-induced reductions in snow cover correlate with coat colour camouflage and resulting mismatch. Specifically, we analysed how mountain hare coat colour mismatch varied between camera trap locations with varying reductions in the number of snow days between the two 30-year averages. We also investigated how 2011-2018 mountain hare moult phenology compared to 1959-1966 and 2011-2018 average snow cover, respectively. Coat colour mismatch was highest in areas with the greatest reductions in the number of snow days. Additionally, 2011-2018 moult phenology better matched 1959-1966 than 2011-2018 snow patterns. Collectively, our results indicate that mountain hares are not adjusting their moult phenology fast enough to track the pace at which snow cover is declining.