PHOENIX – For over 25 years, the endangered Mount Graham red squirrel has been quietly battling population decline atop one of Arizona’s tallest mountains.
Endemic to the Pinaleño Mountains in southern Arizona, this species of squirrel was classified as endangered in 1987, with population numbers ranging from 35 to 550.
Habitat loss, wildfires and food competition have contributed to the dwindling population of Mount Graham red squirrels. Efforts from the Arizona Game and Fish Department, the University of Arizona, the Phoenix Zoo and the U.S. Forest Service, populations have almost doubled in the past year from 144 squirrels to an estimated 233 by end of last year.
“It was fantastic,” said Holly Hicks, a Game and Fish small mammal project coordinator. “We all just felt such relief to know that the population can recover after such a devastating wildfire.”
Mount Graham red squirrel numbers over 200 had not been seen since 2017, when the Frye Fire destroyed much of their habitat. The Frye Fire left approximately 35 squirrels total in the Pinaleños – near extinction.
“The Frye Fire happened over the summer, and our surveys happened in September, so that first year when we were up there after the fire, morale was low,” Hicks said. “People who put their whole life and soul into trying to keep an animal alive, and then to see something like that come through, it definitely can be devastating.”
Threats to Mount Graham red squirrels
Since the fire, conservation efforts have helped red squirrel populations recover from habitat loss, but resource competition with another species, the Abert’s squirrel, has brought up more issues.
The Abert’s squirrels have a bigger frame and a larger habitat range than the Mount Graham red squirrels, so when a fire wipes out much of the habitat for both, the competition for food affects the smaller red squirrels more.
Brought to the Pinaleño Mountains in the 1940s, the non-native Abert’s squirrels share all the same food and nesting grounds as the endangered red squirrels, which poses another threat.
“At the time, the research suggested that the two species – their habitats did not overlap. So the thought was, you could put them on the mountain and they would not have any impacts on any other squirrel species that were up there,” Hicks said. “But, of course, Mother Nature is unpredictable, and so are wildlife, so they have to prove us wrong at some point.”
Much of the Mount Graham red squirrels’ habitat and food source comes from spruce and fir trees, most of which burnt in the Frye Fire. A large number of mixed conifer trees – the Abert’s squirrels’ favorite – remained.
“I think red squirrels are very resilient,” said Bret Pasch, associate professor at University of Arizona’s Wildlife Conservation and Management program. “If you’re going to have an endangered species, red squirrels are a good one to have because they can really tolerate high human footprint.”Human presence on Mount Graham has been a controversial topic in the past, including legal battles over the Mount Graham International Observatory in the 1980s and ’90s. The observatory is located in what was once a prime habitat for the endangered species, but its presence has proved beneficial in some ways, Hicks said.
“They were definitely taking some of the best habitat from the squirrel to put those telescopes in, but in defense of the telescopes, I don’t think that there would be any spruce-fir left on that mountain if it wasn’t for the telescopes,” Hicks said in reference to wildfire mitigation. “When there are structures in place, that’s where the first efforts go in to protect the space.”
The geography of southern Arizona’s Sky Islands ensures that this subspecies’ range will never naturally spread beyond the Pinaleño Mountains. Miles of vast Sonoran Desert isolate each mountain, which means the red squirrels stay on Mount Graham.
Captive breeding program
The Phoenix Zoo started a captive breeding program in 2014 to try to breed a healthy population off-site, in case a fire were to strike Mount Graham again. They house four red squirrels, two male and two female, that have yet to produce offspring.
“We have this vision with our partners of being able to create another population that hopefully can serve as an additional backup on the mountain,” said Tara Harris, Phoenix Zoo director of conservation and science. “The risk of wildfire continues to be quite high for these squirrels, and so having that extra population would be really important for making sure that this squirrel continues to exist here in Arizona and in the world.”
The captive breeding program aims to reintroduce red squirrels into areas of Mount Graham they once occupied in an effort to further rebuild the population and the habitat range.
“We are still chasing that elusive thing, trying to get actual pups born here,” Harris said. “We’re hoping that this breeding season is the one.”
