Among the many mechanisms by which humans have pushed animals to extinction, warming the planet may often have been a contributing factor. However, this is the first time that human-induced global warming, and the sea level rise that comes with it, has been identified as the primary reason for a mammal's demise.
The mosaic-tailed rat (Melomys rubicola) was always a highly vulnerable species; when first recorded in 1845, it was restricted to a 340 by 150-meter (1,100 by 500 feet) coral island called Bramble Cay. With such a tiny range, survival chances were always slim. The arrival of a competitor or changes to vegetation could easily have seen the rat joining the dodo and Tasmanian tiger. Nevertheless, reports from the 70s and 80s suggest the animals were then quite numerous.
However, it is the cause of M. rubicola's extinction that is likely to ensure the obscure rat's place in history. A report concludes that Bramble Cay has been repeatedly inundated in recent years as a consequence of rising seas, and that it is for this reason that the rat has not been seen since 2009, and is now almost certainly extinct.
Bramble Cay lies in the Torres Strait between Australia and New Guinea, and is seldom visited by humans. In August and September 2014, researchers from the University of Queensland placed small mammal traps – baited with rolled oats, peanut butter, and golden syrup – and camera traps throughout the island in the hope of finding some signs of the nocturnal mammal. Empty-handed, the researchers interviewed a fisherman who sometimes stops at the island. He said he had not seen the rat since 2009.
The highest point on the cay is 3 meters (10 feet) above the regular high-tide mark. A rise of 10 centimeters (4 inches) in sea level at nearby locations between 1993 and 2010 has done away with whatever safety margin the rat had, shrinking its area by almost 40 percent. Extreme weather events in the region in recent years have probably put the entire island under water during storm surges.
Even if the animal inhabitants survived inundation, their food supply would not, with plants at the south end of the cay flattened, apparently in a recent storm.
“Significantly, this probably represents the first recorded mammalian extinction due to anthropogenic climate change,” the report notes.
Researchers left no stone unturned in the search for Melomys rubicola. Natallie Waller
Sadly, there appears to be no evidence that these rats left a sinking island for higher ground, although the report adds that M. rubicola may have arrived at the island from Papua New Guinea's Fly River Delta 53 kilometers (33 miles) away, and relatives may survive on islands there.
The discovery is bad news for other local species, with the report noting: “Bramble Cay is the most important rookery in Torres Strait for green turtles (Chelonia mydas) and a variety of seabirds.”
According to one estimate last year, one in six living species will soon follow in its tiny footsteps.
[H/T: The Guardian]