In the Field: Studying a Rare Red Fox
Last winter, while sorting through images from cameras installed in northern Yosemite, wildlife biologists spotted something extraordinary: a Sierra Nevada red fox. The rare mammal had not been seen inside the park for nearly 100 years.
The Sierra Nevada red fox (Vulpes vulpes necator) is one of two native fox species in Yosemite (the other is the grey fox). They’re the only subspecies of red fox (Vulpes vulpes, the world’s most widely distributed carnivore) native to California. They’re shy, smaller and darker than non-native red foxes, with long white-tipped tails and black fur behind their ears. And they’re extremely uncommon: Scientists estimate that only 20-30 of the animals live in the Yosemite/Sonora Pass area.
With support from our donors, Yosemite’s wildlife biologists are working to learn more about this elusive species. They’re using images from motion-activated cameras, as well as hair and scat samples, to study the distribution and diversity of the park’s Sierra Nevada red fox population, while also gaining information about the species that share the fox’s habitat. Predators such as coyotes and mountain lions compete with the fox for prey. Snowshoe hares and Douglas squirrels are important food sources. Non-native red foxes pose a potential threat: Interbreeding could reduce the Sierra Nevada red fox subspecies’ genetic diversity and ability to reproduce.
Ultimately, park biologists aim to use information from the cameras and DNA samples to inform wildlife management decisions that will lead to a self-sustaining Sierra Nevada red fox population.
Earlier this month Ryan, our project coordinator, joined a Yosemite wildlife team for a three-day trip through the park’s northern wilderness to update existing cameras and install new survey stations. Each station is equipped with “scent lures" that helps draw animals into the camera’s view. A hair snare system below the lures captures fur samples that biologists can analyze to learn more about the Sierra Nevada red fox and other animals that visit the stations.
The stations are deep in the backcountry, 15 miles from the nearest trailhead. Ryan’s team spent one field day covering 6 miles off-trail at around 10,000 feet as they set up three new survey stations and reset two existing cameras. For the NPS wildlife crew, those long days of hiking at high elevations are no problem — they’re in prime hiking condition after a summer field season that included work on several other donor-funded projects, from studying how fire affects endangered owls to surveying for bighorn sheep and using environmental DNA to find suitable habitats for yellow-legged frogs.
Before the end of the trip, the team also installed another four cameras near a backcountry lake. Three or four more will be set up next week, for a total of 16 cameras ready to gather snapshots this winter. Along the way, the crew collected eight memory cards containing several thousand photos, which the biologists review for signs of the rare fox and other wildlife.
While the team was in the field, the U.S. Fish and Wildlife Service released a decision that could affect the future of the Sierra Nevada red fox: The agency designated the “Distinct Population Segment” of Sierra Nevada red fox in the Yosemite/Sonora Pass area a Candidate Species under the Endangered Species Act (ESA). As a “candidate,” the fox isn’t added to the Endangered Species List, but the agency acknowledged the threats to the population. As one Yosemite biologist pointed out, there’s a good chance the decision will lead to threatened or endangered federal listing in the near future.
In the meantime, the research that Yosemite’s wildlife biologists are doing could help make that “good chance” a reality, while helping the park map out a path for protecting one of North America’s rarest mammals.