"It seems a fairly sensitive creature to various types of human impacts," said Ivan Scales, a geographer at England's University of Cambridge who studies the effects of human activity on the region's vegetation.
One of the problems with gauging the threat to the giant jumping rat is the lack of historical data about the species, he adds.
For several centuries the forest has experienced successive waves of degradation, Scales says, at the hands of various conquerors, colonists, and migrant cultures, each with different ways of using the land.
Destructive patterns of land use continued into the late 20th century.
Jörg Ganzhorn is a biologist at Germany's University of Hamburg who has studied the genetic diversity of the giant jumping rat.
"When I started working there in the 1980s, the southern extent of their range was about 9 to 15 miles [15 to 25 kilometers] farther south," Ganzhorn said.
Deforestation accelerated in Menabe during the 1980s, Scales explains, when a boom in the price of corn attracted migrants from southern Madagascar hoping to grow the crop for export.
Many of the farmers stayed after the boom ended.
But that alone doesn't account for the reduction in the rats' range, Ganzhorn says.
"We really don't know enough to explain it," he said. "It could be dogs and hunting as well as habitat degradation."
The prognosis for the giant jumping rat may be better than expected, but it is still uncertain.
Madagascar President Marc Ravalomanana has announced plans to create a protected area in the region, but the project is taking longer than expected.
Meanwhile, prospectors have begun using dynamite to search for oil reserves in Menabe, causing concerns about future forest degradation.
"Talking to the villagers, they definitely have an appreciation for the degradation that's happened over the last 30 years," Scales said.
Some residents in the region are learning about the giant jumping rat's ongoing plight through an annual marathon organized by conservation agencies.
On July 31, 33 runners completed the 26-mile (42-kilometer) course starting at the southern limit of the rat's range and passing through one of Madagascar's main tourist attractions, the avenue of baobabs.
Another 112 runners followed a shorter, 13-mile (21-kilometer) route.
"I was surprised to see vazahas [foreigners] running," said a 17-year-old Malagasy student who ran the race.
"They are not usually as fast as us, but they are good too."
Kerri Poore in Madagascar contributed to this article.
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