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Caught on Camera: Sierra Martens and Flying Squirrels Using Wildlife Passage

The adorable Sierra Marten pictured below was caught on wildlife camera in October. The camera was set up to study animal movement under a new road crossing structure known as the “toad road” in Sierra National Forest.

A marten (weasel like mammal) looks up at the camera
A Sierra Marten caught on wildlife camera in October 2019.

The USGS and USFS research team working on the project affectionately call this elevated road segment in Sierra National Forest a “toad road” because it was intended as a potential way for threatened Yosemite toads to pass under roads and avoid vehicle collisions. But the cameras are showing that it’s not just toads that are using this space! The team has been documenting all of the species using the elevated road segment as part of their research. In addition to Yosemite toads, skunk, weasel, rubber boa, gartersnake, and a variety of lizards and rodents have been spotted using the underpass.

The Sierra marten (Martes caurina sierra) is a mammal in the weasel family about the size of a house cat. It lives in high elevation forests of the Sierra Nevada and southern Cascades. It eats mostly smaller mammals, including Douglas squirrels, snowshoe hare, voles, and flying squirrel.

A marten (weasel like mammal) walks under a wooden underpass
A Sierra Marten (Martes caurina sierra) caught on wildlife camera in October 2019 passing beneath an elevated road segment built to study usage of the underpass by the Yosemite toad.

Some of these marten prey have also been spotted on the cameras—the photo below features a Humboldt’s flying squirrel (Glaucomys oregonensis).

Squirrel-like animal looks up at the camera
The photo features a Humboldt’s flying squirrel (Glaucomys oregonensis) caught on a wildlife camera. The camera was set up to study animal movement under a new road crossing structure known as the “toad road” in Sierra National Forest.

This species, found only on the West coast, was classified as a new species distinct from other flying squirrels in North America in 2017, based on mitochondrial DNA. Flying squirrels can’t really fly like birds or bats, but they can glide between trees with the help of the patagium, a furry membrane that stretches from the wrist to the ankle. They also spend time on the ground—perhaps on occasion moving under the “toad road.” It’s not clear yet whether the Humboldt’s flying squirrel is using the elevated road segment to pass under or just hanging out near the cameras, but the research team may find out soon enough.

The study may have started with the Yosemite toad, but the research team has been pleased to observe these mammalian visitors in the course of their work. All of these species face threats to their forested mountain habitat, including wildfires and climate change.


Yosemite toad
A remote capture image of a Yosemite toad seen crossing beneath "toad road" structure built atop a forest road in the Sierra National Forest. Reseachers are exploring tools, such as this elevated road structure, or "toad road," to reduce vehicle strikes to this threatened species.

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