Flying-foxes relocated: but there are challenges ahead

August 2012

The relocation of the grey-headed flying-foxes roosting within the Royal Botanic Garden commenced on the afternoon of 4 June with a cacophony. Each morning since 5 June a team of staff has been present to deter the flying-foxes from roosting within the Garden. We anticipate that measures to deter roosting are likely to be required pre-dawn for months to come.

The State and Commonwealth approvals allow up to 30 minutes of noise to be used around sunset and up to 45 minutes of noise pre-dawn (stopping 30 minutes before sunrise to allow the flying-foxes enough time to fly to an alternative roost). These are the times when the flying-foxes are naturally mobile, flying out to forage during the night and flying in to roost for the day. By targeting these times we have encouraged the flying-foxes to leave the Garden and deterred them from returning.

Timing is everything some people would argue. During April 2012 the number of flying-foxes within the Sydney region was 10 times less than in April 2011. Fortuitously for the relocation, the spotted gum (Corymbia maculata) was flowering in the Hunter region and on the south coast (Kioloa) and flying-foxes flocked in large numbers to both locations (~50 000 each). This meant that there were fewer flying-foxes to be relocated from the Garden.

So where have the flying-foxes gone? The grey-headed flying-fox occurs between Bundaberg in Queensland along the coast down to Melbourne, and over the last few years around to Adelaide. There are over 200 known colonies throughout the species distribution. Studies have shown that individuals move thousands of kilometres across this area and genetically the species forms a single population. That is to say, the flying-foxes observed within the Sydney colonies are the same individuals observed in Brisbane and Melbourne. The monitoring we have conducted has identified that the flying-foxes within the Garden readily move to other colonies within the Sydney region as well as to colonies throughout their distribution. Thus, the relocated flying-foxes have been located within neighbouring colonies (e.g. Centennial Park and Parramatta Park) and colonies throughout NSW and into Queensland.

The challenge we face is to deter any flying-foxes from roosting within the Garden. From the monitoring we have conducted we expect that the flying-fox population within the Sydney region will increase through spring and summer. This may mean that increased numbers of flying-foxes will be attempting to roost within the Garden. The importance of deterring roosting becomes greater during summer as the behaviour of female flying-foxes is to crèche their young that are too heavy to carry while they forage during the night. If this occurs there are limitations to the methods we can use to deter roosting. A consequence of this may be that larger numbers of flying-foxes re-establish roosting within the Garden. The State and Commonwealth conditions acknowledge this and in a worst case scenario allow for a second relocation to be implemented.

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Botanic Gardens Trust, Sydney, Australia

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Flying-foxes relocated: but there are challenges ahead