Glucocorticoids and activity in free-living arctic ground squirrels: Interrelationships between weather, body condition, and reproduction

The dynamic relationship between glucocorticoids and behavior are not well understood in wild mammals. We investigated how weather, body condition, and reproduction interact to affect cortisol levels and activity patterns in a free-living population of arctic ground squirrels (Urocitellus parryii). As a proxy for foraging and escape behaviors, collar-mounted accelerometers and light loggers were used to measure above-ground activity levels and the amount of time squirrels spent below the surface, respectively. Fecal cortisol metabolites (FCMs) were quantified to assess glucocorticoid secretion in squirrels. Male and female squirrels differed in above-ground activity levels and time spent below-ground across the active season, with males being most active during mating and females most active during lactation. We also found that female, but not male, squirrels exhibited seasonal variation in FCM levels, with concentrations highest during mid-lactation and lowest after the lactation period. In female squirrels, the seasonal relationships between breeding stage, activity, and FCM levels were also consistent with changes in maternal investment and the preparative role that glucocorticoids are hypothesized to play in energy mobilization. Body condition was not associated with FCM levels in squirrels. As predicted, deteriorating weather also influenced FCM levels and activity patterns in squirrels. FCM concentrations were affected by an interaction between temperature and wind speed when seasonal temperatures were lowest. In addition, above-ground activity, but not time spent below-ground, positively correlated with FCM levels. These results suggest that, although ground squirrels avoid inclement weather by remaining below-ground, activation of the stress axis may stimulate foraging activity.