Final comments and implications for roost management
State-level management guidelines, including the Flying-fox Camp Management Policy (State of NSW and Office of Environment and Heritage 2018) and the Flying-fox Roost Management Guideline (State of Queensland Department of Environment and Science 2020) outline several camp-based management approaches that involve the modification or removal of vegetation within roost sites. ‘Routine camp management actions’ include the removal of tree branches or whole trees, weed removal, trimming of understorey vegetation, and minor habitat augmentation. The aim of such actions are often to encourage roosting in alternative areas of the roost (e.g. Geolink 2010; EcoLogical 2014), or to increase the sustainability of existing roosting habitat for flying-foxes (e.g. Ku-ring-gai Council 2018). These actions are considered to be low impact activities (Department of Environment and Science 2020b) and do not require referral under the EPCB act (Commonwealth of Australia 2015), however these actions may considerably alter the structure of roost vegetation and decrease the suitability of a roost as habitat (Ku-ring-gai Council 2018). For example, the removal of mature weed vines in the canopy and midstory, as well as the clearing of understory, can reduce the structural complexity of roost vegetation. This may have immediate and direct effects on roosting flying-foxes, and may accidently cause bats to disperse or adjust use of roost trees in ways contradictory to conflict management. This may also have long-term, indirect implications for the ability of flying-foxes to survive extreme weather events, by altering roost macroclimate and removing physical refuge needed at times of extreme heat (Welbergen et al. 2008).
Individual and council-level roost management plans developed by local governments under the guidance of these policies, commonly utilise these vegetation management measures (e.g. EcoLogical 2014; Logan City Council 2015; Sunshine Coast Regional Council 2016; Ku-ring-gai Council 2018), though the long-term implications for flying-foxes of vegetation works are rarely noted (with the exception of Ku-ring-gai Council 2018). We recommend that vegetation removal should not be considered low impact by default. Routine management actions should follow a mosaic pattern (State of NSW and Department of Planning Industry and Environment 2019), or target weeding on a weed-by-weed case basis (Ku-ring-gai Council 2018), and seek to maintain refuges in the mid- and lower storeys at all times. Special care not to disturb bats should be taken in identified core areas of the roost.

Conclusion

This study takes a thorough, multifaceted approach to better understand the ecology of flying-fox roost use and structure in Australia. We build upon broad-scale knowledge of historic roosting occupancy and abundance patterns, and provide updated baseline information on roosting structure in urban and peri-urban roosts by providing fine-scale spatial, and temporal data on roost and tree use. Specifically, we demonstrate high variation in patterns of occupancy and abundance between roosts sites, and provide updated demographic information including the spatial and temporal distributions of males and females within roosts. We also show evidence of sympatry and indirect competition between species, including spatial segregation of black and grey-headed flying-foxes within roosts, and seasonal displacement of both species by little red flying-foxes. The outcomes of this research will be of immediate, practical benefit to management and conservation of flying-fox roosts in Australia, and meets research needs specifically identified in the draft Recovery Plan for the Vulnerable grey-headed flying-fox. The level of spatial and temporal detail provided in our empirical study will be important in designing management plans that are sensitive to flying-fox habitat needs, and in identifying and protecting important habitat areas within roosts that are reflective of current movements and preferences. Most importantly, we highlight that a one-size-fits-all approach to roost management will be inappropriate, given the extent of variation between sites even within a regional area. Fine-scale information on roost tree preferences will also improve understanding of the potential impacts of existing conflict management strategies involving vegetation removal, including buffer creation, and can guide vegetation removal efforts to heed these habitat requirements. This information is timely, and much needed in advance of the recently announced Environmental Trust grants program for flying-fox habitat restoration, and in the face of continued and increasing urbanisation of flying-foxes in Australia.

Acknowledgements

We would like to thank Beccy Abbot, Kirk Silas, Devin Jones, Liam Chirio, Rachel Smethurst and Cara Parsons for their assistance in the field. Fieldwork for this work was supported by a Paddy Pallin Research Grant and a ‘Grants in Need’ science grant awarded to TJL, sponsored by the Paddy Pallin Foundation, The Royal Zoological Society of NSW and The Foundation for National Parks and Wildlife, and the National Science Foundation (a Coupled Dynamics of Natural and Human Systems grant DEB1716698 and a DARPA PREEMPT program Cooperative Agreement #D18AC00031). TJL was supported by an Endeavour Postgraduate Leadership Award and a Research Training Program scholarship sponsored by the Australian Government, AJP was supported by an ARC DECRA fellowship (DE190100710) and a Queensland Government Accelerate Postdoctoral Research Fellowship, RB was supported by a Griffith University Honours Allowance and an EFRI Honours Thesis Write-Up Scholarship, and RKP was supported by USDA National Institute of Food and Agriculture (Hatch project 1015891). This research was conducted under a Griffith University Animal Research Authority permit (DEB-1716698), a Scientific Purposes Permit from the Queensland Department of Environment and Heritage Protection (WISP17455716), a permit to Take, Use, Keep or Interfere with Cultural or Natural Resources (Scientific Purpose) from the Department of National Parks, Sport and Racing (WITK18590417), a Scientific Licence from the New South Wales Parks and Wildlife Service (SL101800) and general and products liability protection permit (GRI 18 GPL), and with permission to undertake research on council and private land. The content of the information does not necessarily reflect the position or the policy of the U.S. government, and no official endorsement should be inferred. We acknowledge the Danggan Balun, Kabi Kabi, Turrbal, Widjabul Wia-bal, Yugambeh and Yuggera Ugarapul people, who are the Traditional Custodians of the land upon which this work was conducted.