Energy Balance in a New Zealand Bat (Mystacina tuberculata): Thermoregulation, Roost Choice, and Diet

Abstract

Seasonal and latitudinal differences in ambient temperature (Ta) differentially impact the energy budgets of endotherms, which maintain homeostasis via physiological and behavioural traits including roost choice, thermoregulation, and diet. During periods of negative energy balance, small mammals, such as bats, use torpor to reduce energy expenditure and therefore energy demands. Most thermal physiological research has focused on species from the extremely seasonal Northern hemisphere, while comparatively few have examined species living in the less seasonal Southern hemisphere. My thesis evaluated how seasonal, and latitudinal differences in energy balance relate to variation in roosting sociality, torpor expression, and diet among three populations of New Zealand lesser short-tailed bat (Mystacina tuberculata). I quantified Ta, roost temperature, and skin temperature responses by individuals and used molecular analysis to compare the diets of three distinct populations (Pureora, Eglinton, and Hauturu). In Pureora, individuals used communal roosts more often in summer than winter, and more often in Pureora than Eglinton during summer. During winter, individuals from Hauturu preferred to roost in uninsulated punga (Cyathea dealbata), which was contrary to Pureora and Eglinton individuals, who preferred insulated tree roosts. Torpor expression was greater for individuals in solitary roosts, in winter compared to summer, and in higher latitude compared to lower latitude sites. In contrast to previous morphology-based diet studies, Lepidoptera and Diptera accounted for nearly 90% of amplicons identified from faecal matter. Dietary diversity was higher in summer than winter, higher in lower latitude compared to higher latitude sites, and higher in juvenile bats compared to other demographics. I demonstrate that M. tuberculata have a varied roosting, thermoregulatory, and dietary strategy, likely to meet the site-specific challenges of their environment.