Australian Rodent, Bramble Cay Melomys, Now Extinct

wild rat

Story at-a-glance -

  • Bramble Cay melomys, small rodents known to live only on an approximately 9-acre low-lying island, Bramble Cay, in Australia’s Great Barrier Reef, have been declared extinct
  • Rising sea levels and storm surges likely destroyed the animals’ food sources and may have washed some of the rodents out to sea, causing them to drown
  • It’s possible a population of Bramble Cay melomys may exist on nearby Papua New Guinea, but this is purely speculative

By Dr. Becker

In Australia, conservationists had spent months planning and gaining permissions for a captive-breeding program for the critically endangered Bramble Cay melomys. These small, mouse-like rodents were known to live only on an approximately 9-acre low-lying island, Bramble Cay, in Australia's Great Barrier Reef.

Unfortunately, by the time the scientists arrived there to try to save the species, no signs of the rodents remained. Surveys of the melomys population were conducted in 2011 and March 2014, which neither detected any of the rodents.

Despite that, The Guardian reported, scientists still believed they would find some survivors in August 2014.

Ian Gynther, a senior conservation officer in Queensland's Department of Environment and Heritage Protection, led the mission to Bramble Cay to retrieve the rodents for captive breeding. He told The Guardian:1

"My colleagues and I were devastated … As each day of our comprehensive survey passed without revealing any trace of the animal, we became more and more depressed."

Last Sighting May Have Occurred in 2009

Bramble Cay melomys were the only mammal endemic to the Great Barrier Reef. When the March 2014 survey failed to detect the species, researchers returned in late August, hoping to find a different fate.

According to a report issued to the Queensland Department of Environment and Heritage Protection, which confirmed the species' extinction:2

"A thorough survey effort involving 900 small mammal trap-nights, 60 camera trap-nights and two hours of active daytime searches produced no records of the species, confirming that the only known population of this rodent is now extinct."

An anecdotal report from a fisherman who visited the cay every year for the last decade suggests the last Bramble Cay melomys were seen in late 2009.

Rising Seas Caused Bramble Cay Melomys to Go Extinct

After realizing the animals had disappeared, the scientists documented the cay's physical environment, measuring herbaceous vegetation and gathering "evidence of physical processes" that may have adversely affected the rodents. The report concluded:3

"The key factor responsible for the extirpation of this population was almost certainly ocean inundation of the low-lying cay, very likely on multiple occasions, during the last decade, causing dramatic habitat loss and perhaps also direct mortality of individuals."

In other words, rising sea levels and storm surges likely destroyed the animals' food sources and may have washed some of the rodents out to sea, causing them to drown. They further added:4

"Available information about sea-level rise and the increased frequency and intensity of weather events producing extreme high water levels and damaging storm surges in the Torres Strait region over this period point to human-induced climate change being the root cause of the loss of the Bramble Cay melomys."

Notably, the melomys were not the only creatures living on the cay. The low-lying island (its maximum elevation above high tide is less than 10 feet) is also home to important turtle and seabird rookeries, which could be at risk from continued sea-level rises and ocean flooding.

Severe Food and Habitat Loss Revealed Over a Decade

Bramble Cay melomys were reportedly first discovered in 1845 by European sailors. There were so many of the rodents at the time that it's said the seamen "sought recreation by shooting the 'large rats.'" The species was formally described in 1924 but by 1978 their population comprised only several hundred rodents, at most.

In 1998, the first formal census of the species was conducted, revealing an estimated population size of 93. By 2002 and 2004, surveys revealed only 10 and 12 individuals, respectively.

Along with declining numbers of rodents, scientists revealed increasingly uninhabitable conditions on the cay, due to erosion by wind, waves and tides.

The area of the cay above high tide decreased by nearly half (to an area of just over 6 acres) by March 2014. The amount of grasses and other herbaceous vegetation, which the rodents used for both food and shelter, also declined from about 5.5 acres to less than 0.1 acres, a loss of 97 percent over the last decade.

Birds roosting among the grasses further lessened the already scarce availability of vegetation to the rodents, which were known to avoid areas with roosting seabirds at night, the report noted. They continued:5

"Given the combination of factors at play, namely the declining trend in abundance of the Bramble Cay melomys (from a very low base) since the 1970s ...

… [T]he very small size of the species' location and the extremely small and diminishing extent of habitat at that location, as well as the likelihood of ongoing severe threats, possibly worsening with time, the species was evidently in severe peril, if not already extirpated [in 2014]."

Are Bramble Cay Melomys Gone Forever?

The scientist are confident that no melomys remain on Bramble Cay, but there's a chance they may not be globally extinct. A possibility exists that the Bramble Cay melomys may exist in the Fly River delta area of southern Papua New Guinea. Although "purely speculative," the scientists suggest surveying the area to find out.

Even the genetics of the species may be, sadly, gone for good, according to The Guardian; the location of tissue samples taken from 42 melomys in 1998 are currently unknown.

If one thing could be learned from the tragedy of the Bramble Cay melomys' extinction, it's that "conservation recovery actions need to be highly responsive," Gynther said, adding that "controversial actions, such as assisted migration for species, must be considered as climate change continues to batter animals and ecosystems."6 In other words, we waited too long to intervene and save this species.