The roosting and foraging requirements of insectivorous bats in an urban environment

© 2013 Dr. Caroline Maree WilsonMost urban areas around the world are continuing to increase in size and density. Urbanisation results in extensive loss and fragmentation of habitat and is a key process threatening the conservation of biodiversity worldwide. Many populations of insectivorous bats (hereafter bats) have declined in urban areas, for reasons that are poorly understood. In order to predict future trends in the distribution and abundance of bats in urban areas, and design cities to provide habitat for bats, a better knowledge is needed of their preferences and requirements for particular habitat elements within the urban mosaic. This project aims to determine the roosting and foraging requirements of bats across Melbourne, Australia. To identify bat roosts and roosting behaviour, I radio-tracked 95 Gould’s wattled bats Chalinolobus gouldii at three sites in Melbourne which represented two urban habitat types: open parkland (Royal Botanic Gardens (RBG)) and regenerated bushland reserves (Valley Reserve and Blackburn Lake (bushland sites)). Large hollow-bearing trees were limited at these sites, which is typical of much of the urban landscape. Chalinolobus gouldii roosted within a range of native and exotic tree species, but showed preference for certain roost tree characteristics (greater DBH, height and decay stage) compared to available trees, as well as certain tree types (e.g. small dead trees). Chalinolobus gouldii used a greater range of cavity types (including dead leaves and loose bark) in Melbourne compared to rural areas (fragmented farmland and extensive forest); possibly in response to a paucity of large hollow-bearing trees. Some evidence was found suggesting bats modified their roosting behaviour in urban environments; this included the greater reuse of roosts at the RBG compared to the bushland sites and in forested areas where more hollow-bearing trees were available. Radio-telemetry was also used to investigate the foraging habitat selection and foraging behaviour of C. gouldii within open parkland (RBG) and a bushland reserve (Valley Reserve). A total of 21 C. gouldii were radio-tracked at night. Bats displayed a preference for foraging in areas with relatively high levels of tree cover and in close proximity to water. Chalinolobus gouldii foraged within the urban matrix, especially around Valley Reserve, where there was less impervious surface in the matrix compared to the RBG. Bats typically foraged within 1 km of their roosts, which is considerably less than what they are capable (Individuals of C. gouldii can forage up to 21 km from their roosts). This suggests that there were sufficient foraging resources close to roosts in this study, which could be attributed to the amount of edges and linear strips of vegetation in urban areas. The provision and protection of trees across the urban landscape will benefit C. gouldii and other bat species which rely on high levels of tree cover. Nocturnal aerial insects and bats were sampled at 60 study sites distributed along an urban-rural gradient. Ten sites each were located within six land-use categories (industrial areas, residential areas, golf courses, recreational parks, remnant bush reserves and riparian vegetation), representing varying levels of human modification. I found that insect abundance and biomass was negatively influenced by urbanisation and positively influenced by number of trees and tree cover. Insect abundance and biomass was greater in riparian and remnant areas than in golf courses, recreational parks and industrial areas. These habitat types also had a higher density of trees than golf courses, recreational parks and industrial areas. A positive relationship was found between insect abundance and biomass and the activity and species richness of bats. Results suggest that managing urban areas to maximise insect abundance, by maintaining diverse and structurally varied habitats, would benefit bat populations. This study highlights the importance of trees as roosting and foraging habitat for bats. The protection of dead, decayed and large old trees is essential for providing roosting habitat. Tree planting and measures to ensure regeneration (i.e. reducing mowing in urban parks) will also provide foraging resources for bats and an ongoing replacement of hollow-bearing trees for roosting. The findings from this study will assist in the formulation of policy and management decisions to ensure the long-term survival of bats in urban environments