Decline of the boreal willow grouse (Lagopus lagopus) has been accelerated by more frequent snow-free springs

Abstract

Climate change has influenced a range of species across the globe. Yet, to state a noted decline in the abundance of a given species as a consequence of a specific environmental change, for instance, spatially explicit long-term data are a prerequisite. This study assessed the extent to which prolonged snow-free periods in autumn and spring have contributed to the decline of the willow grouse, the only forest grouse changing into a white winter plumage. Time-series data of willow grouse numbers from summer surveys across the study area were integrated with local data on weather (snow cover), mammalian predator abundance and hunting intensity. Modelling was conducted with a hierarchical Bayesian Poisson model, acknowledging year-, area-and location-specific variability. The results show that while willow grouse numbers had decreased continuously across the study landscapes, the decrease was accelerated at the sites where, and during the years when the preceding April was the most snow-free. This indicates a mismatch between the change into a white winter plumage and the presence of snow, turning the bird into an ill-camouflaged prey. The results thus also confirm past hypotheses where local declines of the species have been attributed to prolonged snow-free periods. Across our study area, autumns and springs have become more snow-free, and the trend has been predicted to continue. Thus, in addition to conservation actions, the future of a species such as the willow grouse is also dependent on its ability to adapt to the changed environmental conditions.

A genus at risk: Predicted current and future distribution of all three Lagopus species reveal sensitivity to climate change and efficacy of protected areas

“…Willow ptarmigan are also sensitive to changes in climate which influence recruitment rates (Hannon & Martin, 2006;Martin & Wiebe, 2004;Slagsvold, 1975;Steen et al, 1988). In Europe, Melin et al (2020) demonstrated that population declines in Finland were more pronounced in years when the preceding April was snow-free, while Selås et al (2011) showed that chick production in Norway was related negatively to summer temperatures in the two previous years.…”

Iterative model predictions for wildlife populations impacted by rapid climate change

“…Changes in winter climate concern also snow duration, which is now shorter than in the past, due to late snow arrival and early snow melt (Descamps et al, 2017; Liston & Hiemstra, 2011). Late onset of winter has been shown to hamper survival of color molting species including ptarmigan (Henden et al, 2020; Melin et al, 2020), likely due to camouflage mismatch resulting in elevated predation rates (Zimova et al, 2016). We used daily temperature data to calculate mean temperature (°C) in the core winter season (December t −1 –March t ) and onset of winter (Julian day).…”

Fitness and fur colouration: Testing the camouflage and thermoregulation hypotheses in an Arctic mammal

“…Arctic species, such as the Arctic fox Vulpes lagopus, that exhibit colour polymorphisms and undergo seasonal colour moults, are interesting models for testing the relative importance of background matching as a camouflage tactic versus a role for thermoregulation in fur colour polymorphism. Species that undergo colour moult are of special relevance because long-term climate change has the potential to cause a mismatch in the seasonal camouflage that results in higher predation risk (Atmeh et al, 2018;Melin et al, 2020;Mills et al, 2013;Zimova et al, 2016). The Arctic fox has two colour morphs: white and blue.…”