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Bats Lose Out to Historic Trees in Sydney

Flying foxes can defoliate trees, but should the Royal Botanic Garden shoo this vulnerable species from its grounds?

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Flying foxes roost in the trees in Sydney's Royal Botanic Gardens in 2008. (Photo by Sarah Zielinski)

In downtown Sydney, just behind the iconic Opera House, lies the Royal Botanic Garden, 75 acres of flowers, trees and grassy areas first established in 1816 on the site of Australia’s first farm, Farm Cove. The gardens are a place for tourists and the people of Sydney to explore and enjoy, and they’re also a site for conservation research. Because this is one of the biggest green spaces in the city, the gardens are home to plenty of wildlife, including flocks of cockatoos and bats with wingspans a yard wide.

While the cockatoos can be annoying (especially if you’re stupid enough to feed them), the bats—called grey-headed flying foxes—have become a real problem, at least in the eyes of garden management. These mammals are herbivores and leave the human visitors largely alone (though they can at times be incredibly creepy). However, they damage the garden because they defoliate trees. In the more than 20 years since the bats took up residence in the gardens, they’ve killed 28 mature trees, 30 palms and many other plants and damaged another 300. Most worrisome, they settled in the Palm Grove, site of many of the oldest trees in the garden, including historic, exotic species collected from places such as Malaysia and New Guinea. So several years ago the management of the garden decided that the flying foxes had to go.

But grey-headed flying foxes are a species on the decline (IUCN lists them as vulnerable) and protected in Australia. They’ve lost foraging and roosting habitat in many places, and commercial fruit tree growers consider them a pest and kill them (either illegally or with permission from the government).

The Botanic Garden couldn’t kill the bats, though, so they came up with a plan to force them out. They would play recorded noise in late autumn and early winter just before dawn—making it difficult for them to sleep peacefully after a night of foraging—and around sunset, giving them an early wake-up call. The idea is that the bats would be so annoyed that they would decide to roost somewhere else. Wouldn’t you leave a hotel if the people in the neighboring room played loud music when you were trying to fall asleep and you kept getting 3 a.m. wake-up calls?

After several reviews and many delays, the Botanic Garden finally implemented its plan this month. By last week, there were only about 10 bats left in the gardens. The rest appear to have fled a couple of miles south to Centennial Park. The Botanic Gardens will now turn its efforts to restoring the areas damaged by the flying foxes.

The story may not end there, however. The recorded noises will be played only until sometime in July. After that, it would be too disturbing for pregnant flying foxes, who could abort due to the stress, or for new mothers who might be separated from their babies. But flying foxes move seasonally, and come September or October, bats from outside the area could decide the gardens look like a great home.

Garden management is hopeful that the plan will work. After all, the Royal Botanic Gardens Melbourne successfully removed their own grey-headed flying fox population in 2003 using similar methods. Those bats can now be found in nearby Yarra Bend Park.

But was the removal of the flying foxes from the Sydney gardens really necessary? When I first heard of this plan, shortly before my latest trip to Sydney in March, I was sad to hear that the bats would soon be gone. They were one of my favorite memories from my first trip there—looking up on a beautiful fall day to see hundreds of these little Draculas hanging above me. While I was in Sydney this year, I met with Tim Cary, a bat researcher at Macquarie University. He made a good case for why stressing out these animals was akin to torture and contended that the plan was doomed to fail. (Cary suggested tenting the Palm Grove with netting to keep the bats out.)

I also met with Mark Salvio, director of the Royal Botanic Garden, and we spoke at length about the level of destruction, the plans to get rid of the flying foxes and the levels of review and restructuring that the plans had gone through over the years. This isn’t something that is being done without any consideration for the consequences to the grey-headed flying fox species. And as much as I enjoyed the bats during my visits, I could understand that the Garden had placed its foliage as a higher priority–that’s why it exists, to preserve the gardens and their history. (After all, I doubt that the Smithsonian Institution would let its collections be destroyed by, say, insects in the warehouse, even if those insects were an endangered species.)

Did Sydney’s Royal Botanic Garden make the right choice? Is stressing the bats a truly horrible thing to do? Will it even work? We’ll have to wait and see on that last question. As for the other two, I know where Cary stands. Where do you?

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About Sarah Zielinski
Sarah Zielinski

Sarah Zielinski is an award-winning science writer and editor. She is a contributing writer in science for Smithsonian.com and blogs at Wild Things, which appears on Science News.

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