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Small carnivores play an important role in ecosystems, but their often hidden lifestyle makes them generally hard to observe. Camera-trapping methodology shows great promise as a standardized monitoring tool for small carnivores. The European polecat (Mustela putorius) is a species of conservation concern, listed on the Annex V of the EU Council’s Directive on the conservation of natural habitats and of wild fauna and flora. Because of this, EU member states have to report the status of their polecat populations regularly. However, standardized methods to estimate the population size of polecat populations are currently lacking. We present a tube-based camera-trapping system, the Polecam, designed to obtain photographs of the facial masks of individual polecats. We tested the system in four study areas in southern Sweden during Spring and Autumn 2021. We obtained 52 observations of polecats, out of which we were able to identify 38 (73%) to individual. From these observations, we estimated area and season specific estimates of density for five season-area combinations using a multi-session spatial capture-recapture model. Density estimates ranged from 0.84 to 2.7 individuals/1000 ha, similar to the estimates from similar landscapes in other countries in Europe. We also obtained observations of six other species of small carnivores, suggesting that the Polecam could be used for multi-species monitoring, as well as density estimation of European polecats.

Many species show range expansions or contractions due to climate change induced changes in habitat suitability. In cold climates, many species that are limited by snow are showing range expansions due to reduced winter severity. The European polecat Mustela putoriusoccurs over large parts of Europe with its northern range limit in southern Fennoscandia. However, it is to date unknown what factors limit polecat distribution. We thus investigated whether climate or land‐use variables are more important in determining the habitat suitability for polecats in Sweden. We hypothesized that 1) climatic factors, especially the yearly number of snow days, drive habitat suitability for polecats, and that, 2) as the number of snow days is predicted to decline in the near future, habitat suitability in northern Sweden will increase. We used a combination of sightings data and a selection of national maps of environmental factors to test these hypotheses using Maxent models. We also used maps of future climate predictions (2021–2050 and 2063–2098) to predict future habitat suitability. The number of snow days was the most important factor, negatively determining habitat suitability for polecats, as expected. Consequently, the predictions showed an increase in suitable habitat both in the current distribution range and in northern Sweden, especially along the coast of the Baltic Sea. Our results suggest that the polecat distribution is limited by snow and that reduced snow cover will likely result in a northward range expansion. However, the exact mechanisms for how snow limits polecats are still poorly understood. The potential range expansion might result in a population increase of the Scandinavian polecat population, in contrast to many populations elsewhere in Europe, where numbers are declining. Due to polecat predation, the expansion of the species might have cascading effects on other wildlife populations.

Animals often modify their behavior to reduce the effects of adverse weather conditions. By studying wild boar equipped with the Global Positioning System (GPS) collars, we explored the effects of weather conditions on movement and activity patterns across seasons. We found that the most prevailing strategy for wild boar exposed to stressful weather conditions is to reduce movement. Wild boar thus decreased movement at low temperatures and in precipitation during winter. We also found that wild boar increased movement in late summer, and with precipitation during late summer, despite higher food availability and facilitated foraging by the rain. We also confirm previous results that snow depth reduces movement of wild boar, likely by making movements more energetically costly.

Predation risk may affect space use and foraging patterns of prey animals, with strong down-stream effects on diet composition and ecological interactions. Wild boar Sus scrofais a notorious crop raider but also a popular game species, yet little is known about how risk perception of human hunting affects wild boar space use. We studied the effects of human hunting on the movement of GPS-collared female wild boar. We found that the hunting method affected whether the wild boar fled or hid. After fleeing into refuge ranges, wild boar moved less and preferred habitats that provided cover and forage such as mast or crops. This suggests that the wild boar tried to reduce the risk of being detected, and possibly also that they avoided competition with resident wild boar in the refuge by using forage that could not be monopolised. The type of hunting thus strongly affected the type of avoidance behaviour displayed by wild boar, with implications for their movement and space use. This suggests that adjusting hunting method to season could be an important management tool for minimising crop losses.