Influence of urban edges on stress in an arboreal mammal: a case study of squirrel gliders in southeast Queensland, Australia

There is growing recognition that ecological research must expand its focus beyond inference based on pattern-process relationships to the direct measurement of ecological and physiological processes. Physiological assessment is important because vertebrates cope with unpredictable and noxious stimuli by initiating a stress response. However, an over-activation of the acute stress response by numerous novel and potentially stressful anthropogenic pressures, including those associated with urban edges, has the potential to generate chronic stress and a greater susceptibility to disease, reduce fecundity and survivorship. An individual's physiological response to edge habitats with varying degrees of contrast to the adjacent disturbed urban matrix (e.g. major vs. minor roads), may provide insight into their survival likelihood in fragmented urban landscapes. Although demographic changes in wildlife resulting from urbanization have been documented, only recently have physiological consequences been examined. We addressed this problem using a case study of the squirrel glider (Petaurus norfolcensis) in the fragmented urban landscape of southeast Queensland, Australia. Hair samples were used to enable a comparison of hair cortisol levels in individual squirrel gliders, providing an indication of potential stress. We applied a linear mixed-effect modeling approach clustered by patch to quantify the influence of site-level habitat factors and relative abundance comparative to edge contrast on hair cortisol levels. We found that edge type had a strong positive effect on hair cortisol levels; but this depended on the availability of abundant nest hollows at a site. We conclude that individual hair cortisol concentration, providing an index of stress, was lowest in interior habitats and highest in edge habitats adjacent to major roads. Furthermore, gliders occupying low edge contrast habitats adjacent to residential areas and minor roads, and containing abundant tree nest hollows, had low-moderate hair cortisol levels. This highlights the potential importance of these habitats for the conservation of arboreal mammals such as the squirrel glider in urban landscapes.