Tyrone Lavery
Between 2010 and 2015, Tyrone Lavery and his colleagues searched tree hollows and set up camera traps and aluminum boxes. They were trying to capture evidence of the Vangunu giant rat, Uromys vika.
Stretching about 18 inches long with its tail, the vika's body is about the size of a guinea pig. It's been known to eat green coconuts, but researchers had never seen a live rat.
Despite its large size, the giant rat was difficult to spot. Between 2020 and 2021, researchers finally snapped dozens of images of what they believe are four different individuals. The rodents live in the unlogged forests on Vangunu, one of the Solomon Islands.
"It is just very rare," Lavery told Business Insider via email. He's a mammalogist at the University of Melbourne. "Not many of them exist."
He and colleagues from Solomon Islands National University published the images of the critically endangered rats in the journal Ecology and Evolution.
"This comes at a critical juncture for the future of Vangunu's last forests – which the community of Zaira have been fighting to protect from logging for 16 years," Lavery said in a statement.
The Solomon Islands government recently gave a company permission to log the area, the Australian Broadcasting Corporation reported.
Now that there's proof the rats are still living in the forests of Vangunu, the researchers hope the Solomon Islands government will help with the Indigenous community's efforts to conserve its habitat.
"If these forests are not protected, Uromys vika will go extinct," Lavery told BI.
In addition to their small numbers, there were other reasons the rats were difficult to find.
First, they're nocturnal. Second, "they live in dense, complex forests," Lavery said. They often hang out in trees up to 100 feet from the ground.
The Indigenous community at the village of Zaira had deep local knowledge of the rats that relatives have passed down for generations, Lavery said. The researchers asked for their help in locating the vika.
"Local knowledge was essential because this is a rare species, and it's also a challenging environment to conduct research in," Lavery said.
The people at Zaira told the researchers the rats sleep in a species of tree called a Dillenia, which often have hollows in their branches. In addition to coconuts, the vika also eat the local ngali nut (Canarium indicium).
Tyrone Lavery
The researchers placed their cameras accordingly, with most of them located high in the trees. Using a lamp stocked with sesame oil helped lure out the rats, according to the study.
In recognition of the local knowledge that assisted them, the scientists named the species Uromys vika. Vika is the existing Indigenous epithet for the giant rats.
Unlike some invasive rats that destroy island ecosystems, the Vangunu giant rat has lived in the region for millions of years and is part of the food chain.
Based on DNA testing, researchers believe the vika arrived in the Solomon Island region around 3 million years ago. "Uromys vika has been isolated on Vangunu for around 1 million years," Lavery said.
Its ancestors likely hitched a ride on a floating raft of vegetation, traveling from New Guinea, he said.
With an environment that was mostly forest, it made sense for the rats to live in the trees. The only other mammals in the Solomon Islands were bats, Lavery said.
"These rats evolved to carry out similar roles that belong to possums or monkeys in other parts of the world," he said.
They are also likely solitary animals, Lavery said, because they were photographed separately rather than in groups.
