Stress load in European ground squirrels living in habitats with high and low human impact

Anthropogenic land use and its after-effects are potential sources of stress for European ground squirrel (Spermophilus citellus) populations, which increasingly have to cope with human impact throughout the species’ range. To determine whether habitat alteration impacts the stress load of free-ranging populations in Austria, we live-trapped and faecal-sampled individuals both in a nearly unaltered steppe habitat (TD) and in a strongly altered alfalfa meadow (FB). Overall and seasonal faecal cortisol metabolite (FCM) concentrations were analysed and compared between the two study sites. FCM levels of adult males and of juveniles of both sexes were higher at FB than at TD. Adult females showed no such differences, but exhibited increased faecal progesterone metabolites (FPM) levels at both sites during June. Our results indicate that human activities affected stress load in adult males and juveniles. The altered vegetation led to highly abundant food at FB and, together with the isolation of the habitat, caused a high population density. This apparently intensified social stress in certain periods of the active season. Elevated FCM levels in both adult males and juveniles at FB coincided with the period of highest population density, when all juveniles had emerged from the natal burrows, and hibernation had not started yet. At the same time, predation pressure and human recreational activities also peaked. The highest FCM levels were found in juveniles at FB shortly after natal emergence, suggesting that this age class is most vulnerable to social stress, predation and human disturbance. The lack of a measurable stress response in adult females may be due to increased progesterone concentrations attenuating the stress-induced elevation of glucocorticoids.