Data collection
Mountain hares predominately inhabit boreal and alpine habitats. They have a circumpolar distribution spread across Europe and Asia from Britain and Ireland in the west to Japan in the east (Angerbjorn and Flux 1995). They are native to Norway and are found throughout the country, with their distribution ranging from sea level to around 1,600 m, which is above the tree line. Population size within Scandinavia is thought to be decreasing (Pedersen and Pedersen. 2012, Elmhagen et al. 2015, Pedersen et al. 2017) resulting in the species being classified as “near threatened” in the 2015 Norwegian Red List (Henriksen and Hilmo. 2015).
We utilized images from camera traps that were deployed by the SCANDCAM project (viltkamera.nina.no), originally designed to monitor Eurasian lynx (Lynx lynx ) (Hofmeester et al. 2021). Camera traps were deployed in multiple study areas in an extensive grid with approximately one camera per 50 km2 grid cell (Figure 1). For this study, we selected all mountain hare records from the period between 25th November 2010 and 25th June 2019. Images containing mountain hares were recorded at 678 locations from 2010-2019 spanning a latitudinal gradient from 58°N to 69° N and altitudes from 0 to 841 m a.s.l. in Norway (Figure 1). To reduce pseudo-replication, we discarded observations recorded within 60 minutes of the previous observation. Mountain hares and invasive European hares (Lepus europaeus ), which are also present in south eastern Norway (Viken County), were differentiated using the species descriptions contained in Smith et al (2018). When mountain hares were identified, we classified moulting stage in three categories (Zimova et al. 2020a) estimating the proportion of the hares’ coat (excluding the long white belly) which was white. 1) Hares with ≥90% white fur were classified as “white”, 2) hares with ≤10% white fur were classified as “brown”, and 3) all other hares were classified as “moulting”. All images were accessed on viltkamera.nina.no and were visually classified by one of two observers, and quality controlled whenever the observer was uncertain of how to classify the images.