Bush rats are again to reclaim their place on this Australian park

This article is from Hakai Magazine, an internet publication about science and society in coastal ecosystems. Read extra tales like this at

By day, the shrubby clifftops of North Head, a thriving slice of bushland on the northern entrance of Sydney Harbour, Australia, are a well-liked strolling spot for city nature lovers. But when night time falls, this coastal reserve is dominated by a colony of bush rats, one of the frequent native rodent species scampering alongside the shores of southeast Australia. For anybody fortunate sufficient to identify one of many tennis ball–sized rodents, their endearing look units them aside from their invasive kinfolk.

“They’re like little dumplings,” says Viyanna Leo, a wildlife ecologist on the Australian Wildlife Conservancy, a nonprofit group working with the Sydney Harbour Federation Trust to preserve North Head, including “[they’re] fairly spherical and fluffy.”

The 250-hectare headland hasn’t all the time been a bush rat kingdom, although. Following a century of being vilified and exterminated from areas round Sydney Harbour, the bush rat inhabitants in North Head was worn out many years in the past by urbanization, habitat fragmentation, and predation by feral cats and foxes. The reserve was overrun by a gang of black rats, an invasive species that’s discovered on each continent besides Antarctica. While bush rats assist keep the ecosystem’s native species, black rats wreak havoc. At North Head, they wasted no time plundering the burrows and tree hole nests of small mammals and gorging on hen eggs, says Leo. “They have been inflicting plenty of issues.”

But when given the prospect, bush rats will be formidable ecological gatekeepers. In 2014, Leo and her workforce started reintroducing bush rats to North Head to drive out their intrusive counterparts. The rewilding effort is working, with annual wildlife surveys exhibiting that black rat numbers dropped from an estimated 112 in 2019 to 29 by 2020. In May 2021, a mere 9 black rats have been captured. The venture harnesses the bush rat’s innate territorial streak. The native rodents outcompete black rats for habitat and meals, and Leo suspects that North Head will in the future be a bush rat–solely stomping floor. “If they’ve obtained the fort, they will keep the territory,” she says.

Fluffy, tennis ball–sized bush rats will be formidable ecological gatekeepers. After their reintroduction to North Head, Australia, the native rodents started to drive out a gang of invasive black rats. Image courtesy of Wayne Lawler/Australian Wildlife Conservancy.

For the reintroduction effort, Leo and her workforce captured 180 bush rats over three years from considerable populations in Muogamarra Nature Reserve and Ku-ring-gai Chase National Park, each situated roughly 30 kilometers northwest of North Head. The researchers lured the rats into traps with a healthful meal of oats, honey, and peanut butter, then assessed the animals’ genes to make sure they have been various sufficient to construct a flourishing new colony at North Head. After inserting a microchip into every rat, the workforce set the rodents free on the headland. Each yr after their launch, Leo and her workforce have surveyed the inhabitants and picked up tissue samples from rats born at North Head to evaluate how genetic range has held up over time.

The outcomes of a 2022 study coauthored by Leo are optimistic. The first bush rats born at North Head have been extra genetically various than the animals captured at Muogamarra and Ku-ring-gai in 2014, due to the wholesome mixture of distinctive genes within the new inhabitants’s founding members.

While this range had dropped barely by 2019, it was nonetheless akin to that of the Muogamarra and Ku-ring-gai colonies. Leo and her workforce will proceed to watch the North Head rats, however she’s assured they’ve the genetic wherewithal to deal with any environmental shifts that may happen. And the inhabitants is slowly rising: in 2022, the workforce recaptured over 200 bush rats on the headland. “It’s a really strong inhabitants,” says Leo, who expects the colony will probably be much more resilient than the rats in Muogamarra and Ku-ring-gai.

While most reintroductions give attention to giving threatened species a lift, it’s simply as vital to prioritize frequent species in conservation efforts and rewilding tasks, says Emily Roycroft, an evolutionary biologist specializing in native mammals and inhabitants genetics on the Australian National University. For occasion, native rodents act as tiny engineers that form the ecosystems they inhabit, spreading seeds, churning the soil, and maintaining insect populations in examine.

Native rodents present basic ecosystem providers, says Roycroft, who was not concerned in Leo’s venture. “We know that if [rodents] have been as soon as there, they have been enjoying a task.”

Relocating frequent species just like the bush rat may present a great gown rehearsal for riskier reintroductions, provides Roycroft. If one thing goes flawed when reintroducing a typical species, there’s usually sufficient time to tweak the strategy and take a look at once more. But when researchers are coping with a species that’s on the point of extinction, they solely have one shot to get it proper. “It may be the final likelihood for that individual species to ascertain a brand new inhabitants,” says Roycroft.

Leo suspects the bush rats have reclaimed their territory for good at North Head, which is now freed from feral cats and foxes and shielded from city sprawl. “They’re just about established now,” she says. “I feel they’ll proceed to do effectively.”

This article first appeared in Hakai Magazine and is republished right here with permission.



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