Snow cover related camouflage mismatch decreases survival

Abstract: Climate change is expected to decrease winter severity at high latitudes, resulting in reduced days of snow cover. Several mammalian and avian species in the northern hemisphere express a seasonal colour coat (SCC) making them white in winter periods and brown or dark in summer. Reduced number of snow-covered days causes an increasing camouflage mismatch between the white coat of animals expressing SCC and their winter background. Camouflage is thought to be the function of coat colour, lowering detectability by predators. Due to climate change, snow cover is expected to start later in autumn and end earlier in spring at high latitudes. Despite some observed species plasticity in timing of moulting, climate change is occurring at such a rate that plasticity is thought to be insufficient to cope with the changing environment. In this study, decoys resembling the average size of SCC species in Scandinavia were used to assess the difference in detection by predators between mismatched and matched individuals. Decoys were used in camera trap clusters consisting of three camera traps, one with no decoy, one with a white decoy and one with a brown decoy. Clusters were placed during periods of snow cover and after snowmelt to test how a camouflage mismatch affects detection by and interaction with predators in both open meadow habitats and closed forest habitats. Images from camera traps were classified, the data was analysed using generalised linear mixed models and survival analysis to determine which factor explained predator detection best and how being mismatched affected survival of decoys. I found that mismatched decoys attracted more predators in comparison to matched decoys. In addition to increased attraction of predators, survival probability of mismatched decoys decreased more rapid than matched decoys. This effect was stronger in closed forest habitats in comparison to open meadow habitats, hazard of being in open habitats was overall lower than in closed habitats. These results suggest that the decline of populations expressing SCC could indeed be caused by decreased survival due to mismatching camouflage. If adaptation, either morphological or behavioural, is not able to keep up with the rapidly changing environment, species expressing SCC will undergo increased predation pressure potentially causing rapid population declines.