Bramble Cay melomys

The first victim of human-caused climate change

The Bramble Cay melomys or mosaic-tailed rat is considered the first mammal species to be declared extinct primarily or exclusively because of anthropogenic climate change. It lived on the Torres Strait island of Bramble Cay, one of the most narrowly limited habitats imaginable. Bramble Cay is an uninhabited sand island only 150 meters wide and 340 meters long at the northernmost point of Australia, surrounded by a coral reef of the Great Barrier Reef. The Bramble Cay melomys was considered the most isolated Australian mammal. It shared its habitat with numerous seabirds and nesting sea turtles.

Researchers at Queensland University wrote in 2013 about the Bramble Cay melomys that it inhabited perhaps the most unusual and most doomed range of any Australian mammal: an unstable coral island of four or five hectares. It is clear that climate change, which has led to rising sea levels since the early 1990s, has immense effects on an island like Bramble Cay, whose highest point rises only three meters above sea level.

In the Torres Strait, where Bramble Cay is also located, sea-level rise has been particularly high since 1993, at at least six millimeters per year. Between 1993 and 2010 alone, it rose by more than ten centimeters. A higher sea level also affects weather conditions: there were more tropical cyclones and flooding events.

According to estimates, around 97% of the vegetation on Bramble Cay disappeared as a result of repeated inundation. The island area that remains permanently above water shrank from four to 2.5 hectares. During an expedition in 2014, only 650 square meters of the islet were still covered with vegetation, and only two of the eleven plant species that had once lived there remained.

Bramble Cay melomys – fact sheet

alternative name	Bramble Cay mosaic-tailed rat
scientific names	Melomys rubicola, Melomys leucogaster rubicola
original range	Bramble Cay (Torres Strait Islands, Australia)
time of extinction	between 2009 and 2011
causes of extinction	habitat loss caused by climate change, repeated inundation of the island
IUCN status	extinct

How did the Bramble Cay melomys get to Bramble Cay?

No one knows for certain how the rodents reached the remote, isolated coral island of Bramble Cay. In a report on the conservation and taxonomic status of the Bramble Cay melomys for the Queensland Environment Department A. Dennis and D. Storch looked for explanations in 1998.

One of their theories is that there is a previously unknown mosaic-tailed rat population in the Fly River region of southern New Guinea. Bramble Cay lies only 50 kilometers from the mouth of the Fly River. Tree trunks and debris are regularly washed out and end up off the island’s coast. The rats could therefore have arrived there either on driftwood or in canoes of the Papuans, who visited Bramble Cay.

The Fly River region is still poorly explored, especially with regard to mammals, which is why it cannot be ruled out that a Bramble Cay population or a closely related species lives there. So far, however, scientists have found no further Bramble Cay rats despite intensive searches there or on other islands.

Dennis and Storch also have a second theory, which they consider the most likely. In view of the current sea-level changes in the Torres Strait, they assume that the rat from Bramble Cay is a relic species from the time when Australia and Papua New Guinea were connected by a land bridge around 9,000 years ago. This would also explain the close genetic relationship of the Bramble Cay melomys to other mosaic-tailed rats on the Australian mainland.

The number of rats on Bramble Cay steadily declined

The Bramble Cay melomys was discovered in 1845 by the Briton Charles Brampfield Yule, who reached the coral island as commander of HMS Bramble. The European explorers from HMS Bramble also gave the island its name. At that time, the rats were said to be so numerous that the ship’s crew amused themselves by hunting them with bows and arrows.

There were said to have been several hundred individuals in 1978. Another 20 years later, scientists estimated the population at about 98 animals based on 42 individuals caught in live traps. On search expeditions in 2002 and 2004, only ten and twelve animals were counted or caught in live traps. And during the annual expeditions from 2007 onward to study the turtles on Bramble Cay, no one saw a mosaic-tailed rat.

During a short visit to the coral island in 2014, nothing indicated that rats had once lived there. The search with 150 live traps and ten camera traps proved unsuccessful. In addition, the scientists recorded that almost the entire island vegetation had disappeared.

Actually a good plan, but unfortunately too late

Although their search for mosaic-tailed rats on Bramble Cay in 2014 was unsuccessful, a team of scientists came up with an optimistic plan. Under the guidance of Ian Gynther, conservation officer at the Department of Environment and Heritage Protection, they wanted to catch mosaic-tailed rats on the island in order to establish a population in breeding programs. This was intended to prevent the extinction of the species. The fact that they found no rodents during their brief island visits in 2011 and 2014 was attributed to the limited trapping effort they had undertaken.

The scientists wanted to return to Bramble Cay as soon as possible, but it took five months to obtain the required permits for breeding the animals in human care from Australian government authorities and various stakeholder groups. Gynther commented on this in 2016 in an article by Jeremy Hance in the Guardian: “Captive breeding is an expensive undertaking that requires considerable staffing, resources, and time from the parties involved. This applies especially to a breeding program whose duration cannot be foreseen, as would have been the case with the Bramble Cay melomys.”

“By the time it became clear that a breeding program was urgently needed as a conservation measure, it was already too late,” Gynther continued. According to the IUCN, the last confirmed sighting of the Bramble Cay melomys was in 2009. It probably went extinct sometime between 2009 and 2011—2015 would have been the starting point for the breeding program.

Bramble Cay melomys: Its extinction was foreseeable and avoidable

John C. Z. Woinarski, an ornithologist at Australia’s Charles Darwin University, and colleagues published a report in 2016 in which they identify decisions and procedures, for example in politics, management, or research, as well as deficiencies that stand in the way of protecting biological diversity.

The Bramble Cay melomys was one of three vertebrates endemic to Australia that became extinct between 2009 and 2014. The other two are the Christmas Island pipistrelle and the Christmas Island forest skink. The extinction of all three species was foreseeable and probably also avoidable, the scientists said.

In the case of the mosaic-tailed rat, Woinarski complains that the precarious situation of the rodents had been known for years. He assumes that the disappearance of the species was due above all to the underfunding of conservation programs. In addition, the Bramble Cay melomys may not have been charismatic enough to attract more public attention. A koala (Phascolarctos cinereus) is certainly much more successful in this regard.

Peter Hannam also pointed out in a 2019 article in the Sydney Morning Herald that the Recovery Plan for the Bramble Cay Melomys published by the Australian government in 2008 downplays the risks the rats were exposed to. According to the plan, the effects of climate change, such as sea-level rise and more frequent tropical cyclones, were not expected to have any major impact on the mosaic-tailed rat population.

Tragically, an earlier draft of the recovery plan contained the proposal to establish individuals on the island through breeding mosaic-tailed rats in breeding programs, the IUCN writes. This point was removed from the final approved recovery plan. And with it, the most effective possibility of saving the species from extinction. Instead, the ultimately approved plan included measures that were either never implemented or were insufficient to prevent the disappearance of the Bramble Cay melomys.

Melomys: a genus with numerous island endemics

Shortly after Charles Brampfield Yule first took notice of the rats living on Bramble Cay, the naturalists John MacGillivray and Joseph Jukes, hired on HMS Fly, visited the island in May 1845. They took one specimen of the unknown rat species back home—the later holotype. On the basis of this specimen, the British zoologist Oldfield Thomas finally described the species scientifically in 1924 as Melomys rubicola. The holotype is now housed in London’s Natural History Museum.

The genus of mosaic-tailed rats (Melomys) comprises 23 species. They are distributed in eastern Indonesia, New Guinea, and Australia. Most species are island endemics whose range is restricted to a single island. This also means that many species are classified by the IUCN as endangered or critically endangered. The biology and ecology of most mosaic-tailed rat species are still little studied, and this also applies to the Bramble Cay melomys.

Like all mosaic-tailed rats, it had a long, hairless tail with mosaic-shaped scales and a prehensile tip. Its soft fur was reddish brown, with a somewhat lighter underside. Compared with its three Australian relatives on the mainland, the rats on Bramble Cay were larger. Their ears, by contrast, were comparatively small.

Like other members of the genus, they seem to have been nocturnal, because observers saw numerous animals gorging themselves in the darkness on the herbaceous and coastal vegetation growing on Bramble Cay. During the day, they sought shelter in crab burrows and tree trunks.

In general, biologists assume that mosaic-tailed rats feed vegetarianly, for example on fruits, berries, and plants. In an article published in 1998 about the natural history of the Torres Strait island of Bramble Cay in the Atoll Research Bulletin, however, coastal researcher Joanna Ellison provides indications that the rats on Bramble Cay may have been different. Ellison found rat tracks leading to turtle nests. She also claims to have seen rats eating turtle eggs.