Nursing females are more prone to heat stress: Demography matters when managing flying-foxes for climate change

Determining the underlying mechanisms responsible for species-specific responses to climate change is important from a species management perspective. The grey-headed flying-fox, Pteropus poliocephalus, is listed as vulnerable but it also a significant pest species for orchardists and thereby presents an interesting management conundrum. Over the last century, the abundance of the grey-headed flying-fox, P. poliocephalus, in Australia has decreased due to a variety of threatening processes but has increased in abundance in urban areas. These flying-foxes are highly susceptible to extreme heat events which are predicted to increase in the future under climate change scenarios. Exceptionally hot days result in many deaths, the majority of whom are females with dependent young. This study examined the behavioural responses of roosting P. poliocephalus to temperature during the summer in their daytime roosts. Bats spent about 30% of their time resting at low temperatures, however, as temperature increased, fanning displaced resting as the predominant behaviour as bats attempted to cool themselves. Females with nursing young fanned significantly more often (P=0.001) and at a higher rate with rising temperature (P<0.001) than males and females without young (average proportion of time fanning 27%, 19% and 16%, and 4.6, 2.8 and 2.5 for gradient respectively). As a consequence, nursing females also rested less with rising temperature than the other demographic groups (P<0.001). These behavioural indicators suggest that nursing mothers are more vulnerable to heat stress than any other demographic category studied. The data highlight a clear need to monitor the most vulnerable demographic units as part of any species management program.