Coping with extreme free cortisol levels: Seasonal stress axis changes in sympatric North American flying squirrels

Most environments exhibit predictable yearly changes, permitting animals to anticipate them. The hypothalamic-pituitary-adrenal (HPA) axis is a key physiological pathway that enables animals to cope with such changes. Monitoring glucocorticoid (the end products of the HPA axis) levels in wild animals throughout the year can improve our understanding of how this pathway responds to different conditions. For this study, we collected 18 months of data on two species of North American flying squirrels (Glaucomys sabrinus and G. volans) living in a southern Ontario forest where temperature and food availability fluctuate dramatically throughout the year. These squirrels are active year-round, nest communally, and rely on scatter hoarded foods in the winter months. Flying squirrels have extremely high levels of free plasma cortisol relative to other mammals, but it is unknown how these levels are affected by environmental and reproductive factors. For both species, our goals were to (1) validate an enzyme immunoassay (EIA) to measure their fecal glucocorticoid metabolite (FGM) concentrations and (2) assess yearly differences, seasonal changes, and the influence of sex, reproduction, and ambient temperature on FGM concentrations in each species. In the lab, we successfully validated the use of antibody 5α-pregnane-3β, 11β, 21-triol-20-one EIA for FGM analysis in both species. In the field, neither sex nor reproductive status (breeding condition or not) were linked to FGM concentrations in either species. FGM concentrations were higher in autumn compared to the spring and summer. There were no other seasonal differences. We discuss possible explanations for the autumn peak in FGM concentrations (increased energy expenditure and social nesting changes), as well as outline possible avenues for future research. Understanding how individuals and populations respond to environmental change is a critical goal in evolutionary ecology, particularly in the context of a rapidly changing Anthropocene.

Effects of environmental factors on the behaviour and nest group sizes of Smith's bush squirrels, Paraxerus cepapi, in a Zambezian bioregion

The responses of wildlife to environmental factors are of conservation importance. However, the absence of relevant information due to inadequate studies, and lack of understanding of the influences of environmental factors on wildlife, particularly in the Zambezian bioregion, remain a conservation concern. For instance, there is a shortage of knowledge on the relationship between fixed effects of environmental factors and behaviour as well as nest group sizes of Smith’s bush squirrels, Paraxerus cepapi Smith, 1836. Our study examined the relationship between fixed effects of several environmental factors (i.e., with focus on ecological factors) and the behaviour as well as nest group sizes of the bush squirrels in and around Zambia’s Chembe Bird Sanctuary (CBS). Flight initiation distances (FIDs) as an index of bush squirrel behaviour, and nest group sizes were simultaneously surveyed to understand the drivers of biological and population responses, respectively. The results revealed that higher tree height (m) and larger canopy coverage (%) could increase FIDs for bush squirrels. The nest group sizes of bush squirrels could also increase with canopy coverage (%) and presence of termite mounds. By focusing on the two different squirrels' responses, the results of this study highlight the most important environmental factors to consider in minimizing the impacts of human activities on bush squirrels, especially in conservation planning and management by taking into consideration the bush squirrels’ natural history, habitat protection and safe distance between humans and bush squirrels.