Behaviour and HPA axis activity differ but are not correlated among urban versus rural eastern grey squirrels (Sciurus carolinensis)

Abstract

Urbanization is one of the greatest threats to the natural world, therefore, it is a pressing need to understand how wildlife populations are responding to anthropogenic environment. This study investigated whether behaviour and hypothalamic pituitary adrenal (HPA) axis activity (i.e. stress) differed between urban and rural eastern grey squirrels and whether behaviour correlated with HPA axis activity. I characterized behaviour using open field tests (OFT) and quantified stress physiology via two hormone metrics: 1) acute dexamethasone-ACTH hormone challenges to measure HPA axis responsivity and 2) fecal glucocorticoid metabolites (FGMs) to assess integrated glucocorticoids levels. I found that urban squirrels tended to be more active during the OFT, have reduced HPA responsivity and elevated FGMs compared to their rural counterparts. However, phenotypic correlations between behaviour and HPA metrics were absent. Therefore, this study advances our knowledge of phenotypic differences and their correlations among urban and rural squirrel populations.