COS 92-4 - Success in the city: A case study of urban tolerance in an Australian bat species

Abstract: The rapid expansion of cities worldwide is introducing unprecedented environmental conditions, forcing species to adjust or go locally extinct. Previous studies have shown that the most ‘urban adapted’ species are those that can increase in density via increased offspring production, higher adult survival, and higher immigration rates. However the extent to which each strategy is employed and the potential condition or fitness costs to successful urban fauna is unknown.

Gould’s wattled bat, Chalinolobus gouldii, is Australia’s most common urban bat species. In this study, we compared life history and condition traits among populations of C.gouldii using a mark-recapture approach asking ‘is there a life-history tradeoff between condition and reproduction in urban areas’? We examined age structure, recruitment and two measures of body condition (an index of wing damage and ectoparasite load) among populations occurring at 10 bat box sites along an urban gradient (ranging from sites with 1 dwelling per ha to 15 dwellings per ha). We predicted that urban sites would have greater rates of immigration or recruitment, but contain individuals in poorer condition.

We found C. gouldii was the most dominant bat box user (n=520 bats banded), however we also recorded significant box use by six other species. Chi-squared tests revealed no difference in the age structure of populations along the urban gradient, with the proportion of adults and juveniles remaining consistent. Levels of wing damage also did not vary between populations (p > 0.05). Using general linear mixed models, we found no difference in the abundance or diversity (p > 0.05) of bat ectoparasites per individual bat along the urban gradient.

No change in life history and condition traits among bat populations along our urban gradient suggest this species is highly adapted to urban life. Gould’s wattled bat may be responding to urban land use change at a larger spatial scale than measured here, or alternatively life history and condition traits may instead respond to variations in climate, food and roost resources rather than ‘urbanisation’ per se. Longer-term monitoring along a larger gradient is recommended to improve understanding of how this species copes in challenging environments. However, knowledge on where and how bats use bat boxes is greatly needed to improve habitat management to cater for a greater number of bat species in urban areas.