Hybrid camouflage variation: Snowshoe hares molt from a brown coat to a white coat in winter. In some populations, however, where winter snow is less extensive, hares molt from a brown coat to a brown coat. Jones et al. show that regulation of the pigmentation gene Agouti is responsible for the winter coat color change. Hybridization with jackrabbits has led to introgression around this gene that facilitates the brown winter morph. Hybridization appears to have provided important adaptive variation to the snowshoe hare. Science , this issue p. 1355

Changing coats with the season: Many species of mammals and birds molt from summer brown to winter white coats to facilitate camouflage. Millset al.mapped global patterns of seasonal coat color change across eight species including hares, weasels, and foxes. They found regions where individuals molt to white, brown, and both white and brown winter coats. Greater proportions of the populations molted to white in higher latitudes. Regions where seasonal coat changes are the most variable (molting to both brown and white) may provide resilience against the warming climate.Science, this issue p.1033

Wildlife must adapt to human presence to survive in the Anthropocene, so it is critical to understand species responses to humans in different contexts. We used camera trapping as a lens to view mammal responses to changes in human activity during the COVID-19 pandemic. Across 163 species sampled in 102 projects around the world, changes in the amount and timing of animal activity varied widely. Under higher human activity, mammals were less active in undeveloped areas but unexpectedly more active in developed areas while exhibiting greater nocturnality. Carnivores were most sensitive, showing the strongest decreases in activity and greatest increases in nocturnality. Wildlife managers must consider how habituation and uneven sensitivity across species may cause fundamental differences in human–wildlife interactions along gradients of human influence.

Increasingly, measures of glucocorticoid levels (e.g., cortisol), key components of the neuroendocrine stress axis, are being used to measure past hypothalamic-pituitary-adrenal (HPA) activity to index psychological and physiological stress exhibited by wildlife for assessing individual and population-level well-being. However, many intrinsic and extrinsic factors affect HPA activity in animals. Using American black bears (Ursus americanus; n = 116) as an ecological model and hair cortisol concentration (HCC) as an integrative measure of past HPA activity, we evaluated the influence of diet, sex and the social environment on black bear HCC in a free-ranging population that spanned adjoining ecoregions with differing densities of potential conspecific and heterospecific competitors. HCC varied by sex, with female HCC ranging from 0.6 to 10.7 pg/mg (median = 4.5 ± 1.2 mean absolute deviation [MAD]) and male HCC ranging from 0.5 to 35.1 pg/mg (median = 6.2 ± 2.6 MAD). We also observed a three-way interaction among sex, δ¹⁴C and ecoregion, which may indicate that some differences in HCC between female and male black bears results from variability in the nutritional needs of larger-bodied males relative to smaller-bodied females, slight differences in food resources use between ecoregions as well as sex-based differences regarding the social environment. Once we understand what drives sex-specific differences in HCC, HCC may aid our understanding of the physiological responses by bears and other wildlife to diverse environmental challenges.

The distal gut is home to the dynamic and influential gut microbiome, which is intimately linked to mammalian health by promoting and facilitating countless physiological functions. In a time of increased anthropogenic pressures on wildlife due to widespread habitat destruction, loss of natural prey/foods, and rapid urbanization, the study of wildlife gut microbiomes could prove to be a valuable tool in wildlife management and conservation. Diet is one of the most influential determinants of a host’s gut microbiome; yet many wildlife agencies allow baiting to facilitate wildlife harvest, although the impact of human-provisioned foods on wildlife gut health is largely unknown. We used stable isotope analysis derived from carbon (δ ¹³C) to index the use of human-provisioned foods by 35 legally harvested American black bears (Ursus americanus), and16S rRNA gene amplicon sequencing to examine the impact of human-provisioned foods on the gut microbial diversity of black bears. We found that greater long-term consumption of human-provisioned foods was associated with significantly reduced microbial species richness and phylogenetic diversity. Our results indicate that consumption of anthropogenic foods through baiting significantly alters the mammalian gut microbiome.