Environmental variability and allostatic load in the Eurasian red squirrel Sciurus vulgaris

The analysis of eco-physiological parameters in wildlife may represent a priority for their conservation and management, not only to establish causal relationships, obtaining a set of raw data, but also to monitor the effectiveness of management strategies. We studied Hair Cortisol concentration (HCC) in Eurasian red squirrels Sciurus vulgaris in four selected study areas in Italy. Areas differed from one another for vegetation type, degree of urbanization and anthropic disturbance, density of red squirrel populations and presence or absence of alien squirrel species. HCC measurements showed the highest values in a high-density population, subjected to a high predation pressure (i.e. in areas characterized by deciduous vegetation). Conversely, the lowest HCC levels have been observed in areas with the lowest squirrel density, i.e. in urbanized environments, where the species is established for a rather long time, and in areas with mixed vegetation and presence of conifers. Measuring HCC provides reliable information on the long-term activity of hypothalamic-pituitary-adrenal (HPA) axis and associated allostatic load. Furthermore, it constitutes a non-invasive method of investigation. The use of hair tubes further supports our non-invasive approach. Because of its simplicity and low costs, hair collection might be applied to monitor the long-term physiological response of wild species even in larger areas, besides focusing in the promotion of citizen-science data collection. Graphic abstract