Large urban trees are keystone structures for Australian microbats

Large trees are keystone structures for a range of taxa. Insectivorous bats depend on large trees for roosting habitat, such as hollows and peeling bark, as well as habitat for their prey. However, large trees are in decline in urban areas globally. We sought to determine if the richness and activity of insectivorous bats in urban environments is associated with the occurrence of large trees; and in which urban landscape context large trees have greatest benefit for insectivorous bats. Using ultrasonic bat detectors set at 83 sites spanning temperate and subtropical cities in eastern Australia, we identified 20,026 bat passes from 16 microbat species and four species complexes. We found strong positive associations between four bat metrics (mean nightly activity, richness and activity of edge-adapted bats and vespertilionid bat activity) and the number of large trees ≥50 cm DBH. We also found evidence that large trees supported a higher richness of edge-adapted bats in areas with lower woody vegetation cover. Our data indicate that the value of large trees for edge-adapted bats is enhanced when large trees are isolated – a relationship previously demonstrated for birds but not bats. Large trees in urban greenspace, especially trees in isolation, offer valuable habitat that supports a substantial community of insectivorous bats. Our results highlight the importance of retaining large, isolated trees (both native and non-native) in urban greenspace for bat conservation.