Vangunu giant rat photographed for the first time

A total of four specimens of the extremely endangered rodents fell into camera traps. © Photo courtesy of Dr Tyrone Lavery

It is about twice as big as a domestic rat and even cracks coconuts: so far, the species of giant rat on the South Sea island of Vangunu, discovered in 2017, was only documented by a half-decayed specimen. But now four of the tree-dwelling rodents have fallen into camera traps. Unfortunately, these could be the first and last images of this island species. The scientists report that commercial logging is now set to begin in the small distribution area of ​​the Vangunu giant rat.

The story of the discovery of the mysterious rodent began with stories from the locals of the 509 square kilometer South Sea island. They reported a particularly large rat that lives in the trees of Vangunu's original forest and can even gnaw coconuts. This animal, known as “Vika”, piqued the interest of researchers led by Tyrone Lavery from the University of Melbourne. Because they suspected it could be a previously unknown species of rodent. But attempts to capture the animal using camera traps initially failed: peanut butter as bait only attracted the domestic rat (Rattus rattus) that had been introduced to Vangunu. So are “Vikas” perhaps just large specimens of these common rodents?

A chance discovery finally revealed that this was not the case: while felling a tree in the remaining primary forest in southern Vangunu, a strange rat was killed and then kept by the workers. In a half-decayed state, it ended up in the hands of Lavery and his colleagues. Their anatomical and genetic studies finally confirmed that it was actually a previously unknown representative of the small group of mosaic-tailed giant rats. According to its native name, it was then scientifically described for the first time in 2017 as Uromys vika. Like the other ten known members of its family, the Vangunu giant rat is characterized by its enormous size, measuring around 45 centimeters in total length.

Lured in front of the camera with sesame oil

Since 2017, however, the only evidence of the newly discovered species has been a single, half-decayed specimen. That's why Lavery and his colleagues decided to conduct another search using camera traps. With the support of the residents of the town of Zaira in southern Vangunu, they once again set up their devices in the rats' small habitat. They experimented with an alternative to peanut butter as an attractant: As the team reports, the Vangunu giant rat's preference for sesame oil became the secret to the success of their search. The scent of this substance even attracted four specimens of the rare rodents into the camera traps.

The researchers were able to clearly assign these animals to Uromys vika based on their at least twice the size of domestic rats and the characteristics of their tails and ears. There were two males and two females, who in turn differed from each other based on individual body characteristics, the researchers write. “The images document that the Vangunu giant rat still lives in the primary forests of Zaira - which, however, represents the last remaining habitat for this species,” says Lavery.

The first and last pictures?

He and his colleagues hope that their publication and the attention it brings can now benefit the protection of this ecosystem. “The results come at a critical time for the future of Vangunu’s last forests,” says Lavery. As the team reports, the residents of the village of Zaira have been fighting for 16 years to have the forest declared a protected area. But on November 1, 2022, the bad news came: the government of the Solomon Islands opened the area for commercial felling because of the particularly sought-after wood.

However, local representatives have appealed against this decision. The renewed detection of the Vangunu giant rat could now be helpful. Because, as the researchers write, destroying the forest would contradict an agreement signed by the government of the Solomon Islands. In it, it commits itself to protecting endangered species from extinction. Lavery concludes: “If the planned logging goes ahead, it will undoubtedly lead to the extinction of the Vangunu giant rat.”

Source: University of Melbourne, specialist article: Ecology and Evolution, doi: 10.1002/ece3.10703

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