Seasonal Coat Colour Moult and Mismatch in Ezo Mountain Hares ( Lepus timidus ainu ): Phenotypic Plasticity and Snow Cover Effects in Hokkaido, Japa

ABSTRACT

Seasonal coat colour (SCC) moult has evolved in numerous species to maintain camouflage in contrasting seasonal environments. Variations in snow cover patterns, particularly shifts in the timing and duration of snow cover, increase challenges for coat colour‐changing species, yet few studies have evaluated how mountain hares ( Lepus timidus ) in Asia respond to these changes. Here, we study how SCC moult phenology and coat colour mismatch in Ezo mountain hares ( Lepus timidus ainu ), a subspecies endemic to Hokkaido, Japan, differ between seasons and between years, and how these patterns are influenced by snow cover and ordinal day (photoperiod). We compared spring and autumn moults between 2 years (2021 and 2024) with contrasting snow‐cover conditions at Takino Suzuran Hillside National Government Park, Hokkaido, Japan. In 2021, snowmelt occurred earlier in spring and the onset of persistent snow cover occurred later in autumn, and 2024 was characterised by later spring snowmelt and an earlier onset of persistent snow cover in the autumn. Using camera traps, we quantified SCC moult phenology and the occurrence of coat colour mismatch and analysed their relationship with snow cover and ordinal day using Bayesian multinomial logistic regression. Our results revealed distinct seasonal moult phenology, with an earlier spring moult in 2021 than in 2024, while autumn moult phenology remained consistent between years. Coat colour mismatch occurred predominantly in autumn in both years and in spring only in 2021. In spring, snow cover significantly increased the probability of hares retaining a white coat, whereas snow cover had no significant effect on autumn moult. This is the first detailed quantification of SCC moult phenology and coat colour mismatch in mountain hares in Asia, addressing a key geographic gap in SCC moult phenology research. Our findings are consistent with patterns reported in mountain hares in Europe and snowshoe hares ( Lepus americanus ) in North America, while also revealing region‐specific dynamics in Hokkaido, where SCC moult phenology shows strong seasonal dependence and limited differences between years. Together, these results highlight the need to understand moult dynamics in mountain hares in Japan and how environmental conditions, particularly regional snow cover, influence moult phenology and mismatch risk in snow‐adapted species, and are consistent with phenotypic plasticity, although between‐year variation does not allow inference of individual‐level plastic responses.