The Bramble Cay melomys (Melomys rubicola) was a small rat with one of the most unusual distributions of all mammals. As far as we know, the only place it occurred was the tiny Bramble Cay in the eastern Torres Strait, at the tip of northern Australia. (This sandy island is only about four hectares, or nine acres, in size.) All islands close to Bramble Cay support another closely-related species, the grassland melomys (Melomys burtoni).
Just how the Bramble Cay melomys became isolated on such a small, remote island remains a mystery. One idea is that it might have become stranded there when sea levels rose following the last ice age about 12,000 years ago. Because of the remoteness of Bramble Cay, what we knew about this animal was very limited. It fed on the low-growing succulent plants that covered the island, and by day it was found sheltering under debris, including dead turtle shells!
From the few reports available since the 1980s, we knew this species was becoming rare. However, by the time we were able to visit the cay to check on the melomys, it was too late. Our surveys could not find any sign of the animal. The cay is small with limited vegetation, so we can be very confident Bramble Cay melomys is now extinct from the only place it was known to occur in the world.
In the Torres Strait, sea levels have been slowly rising over the past 15 years. On Boigu and Saibai Islands, the ocean often floods people’s homes. In 2009, these rising seas were made worse by a big storm surge that pushed the sea well above normal levels. These high sea levels had big consequences for Bramble Cay’s vegetation, which was the melomys’ only food source. By comparing historical photographs, we can see that the area of plants found there today is only a fraction of what once occurred on the island. Logs and other debris found on the cay show that it has been flooded by salt water, causing the vegetation to die back.
We are confident the extinction of Bramble Cay melomys resulted from the combination of rising sea levels and storm surges killing off its only food source. It therefore appears to be the first extinction of a mammal caused by human-induced climate change. This example is clear because Bramble Cay is such a tiny island, but it may not be considered an unusual event in the future. There are many examples of species that are found only on tiny islands or mountain tops that may be facing similar threats from climate change in the near future.
Dr. Tyrone Lavery is a Negaunee Interdisciplinary Postdoctoral Fellow at The Field Museum. His research focuses on mammals of the Southwest Pacific and how the species on different islands have been shaped by interactions with the people that live there.