By Sean Munoz, Communications Intern
High in the rugged mountains of southeastern Arizona, a squirrel fights for its survival. The Mount Graham red squirrel, Tamiasciurus fremonti grahamensis, an elusive subspecies found only in the isolated peaks of the Pinaleño Mountains, has become a symbol of both ecological fragility and resilience in the face of endangerment. Once abundant in its sky island home, the Mount Graham red squirrel is listed as endangered, with an estimated population of fewer than 250 individuals remaining in the wild. The subspecies’ struggle is a complex web of habitat loss and fragmentation, climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.
Learn more about climate change , and the ongoing tension between development and conservation.
Unique Habitat
Mount Graham is the highest peak in the Pinaleño Mountains, which are part of the sky islands, a collection of isolated mountain ranges scattered across southern Arizona. The sky islands are specific mountaintops surrounded by a contiguous sea of desert, offering unique biomes including mixed-conifer and spruce-fir forests, crucial for species like the Mount Graham red squirrel.
These ranges, which rise dramatically from the surrounding desert floor, provide a rare microcosm of biodiversity, harboring species found nowhere else on Earth. The Mount Graham red squirrel is one such species. Its home is found only in the conifer forests of the upper elevations of the mountain, where it creates its midden—a collection of past meals and cool storage for future ones located at the base of tree. It survives on a diet of mainly conifer seeds and fungi.
Current Challenges
Over the past few years, the Mount Graham red squirrel has faced severe challenges in its native habitat. Threats like wildfires, climate change, human impact, and nonnative species have left this squirrel struggling for a place to call home. The introduction of Abert’s squirrels in the 1940s has also caused problems for the Mount Graham red squirrel.
“They have all of the same food and nesting resources,” said Brittany Garza, a U.S. Fish and Wildlife Biologist. “Abert’s squirrels are more adapted to open environments, which can lead to competitive pressure on the red squirrel in places where the forest has opened up because of wildfire.”
Endangered Species Listing
First listed as endangered in 1987 under the Endangered Species Act, the Mount Graham red squirrel has experienced a roller coaster of a growing and declining population. After the devastating Frye Fire in 2017 reportedly left the population with 35 individuals, red squirrel experts worked with the Forest Service to develop a feeding program to provide food for the squirrels using feeders placed near their remaining middens.
“The Forest Service put on their snowshoes and hiked 35-pound bags of rodent chow out to these places to keep food in the feeders. We were really worried that the squirrels’ middens in which they cache all their food for the winter had burned and we didn’t know if they could make it through the winter, so we wanted to supply them with food at that time,” said Marit Alanen, a U.S. Fish and Wildlife Biologist. The Arizona Game and Fish Department also works with the Forest Service and U.S. Fish and Wildlife Service to host an annual census, where participants count active squirrel middens. In 2024, the population estimate was 233, a substantial rise from the estimate of 35 in 2017. This shows the squirrel subspecies has strong tenacity to keep its place in our world.
Preserving and Increasing the Population
Biobanking is one modern solution to this problem. Taking a small tissue sample such as an ear punch has allowed the U.S. Fish and Wildlife Service to store genetic material to possibly bolster future populations with squirrels potentially cloned from these founding genes.
Brian Small, a U.S. Fish and Wildlife Biologist focused on recovery and restoration says, “By making proactive decisions now, we’re able to take a more thoughtful approach to collections, rather than waiting until it’s too late. This foresight allows us to act at a time when biological diversity is critical. We know that high diversity is indicative of a healthier system, and maintaining that diversity is key to preserving ecosystem health. By capturing and preserving more of this diversity, we increase the chances of sustaining a resilient and healthy system for the future.”
The Frozen Zoo® at the San Diego Zoo Wildlife Alliance holds 11 samples taken from these red squirrels and each holds the possibility of ensuring the continued survival of the Mount Graham red squirrel. These samples, carefully collected and preserved, could ultimately contribute to the subspecies’ recovery and help mitigate risks from population decline.
The Arizona Center for Nature Conservation (ACNC) at the Phoenix Zoo also has a captive breeding pilot program with the goal of breeding these squirrels and releasing them back into the wild. The program has been ongoing for about 10 years, with just a few squirrels being kept at the Phoenix Zoo as part of the pilot project. There have been challenges in breeding squirrels in captivity, but the Zoo has made some remarkable discoveries.
“The squirrels are proving to be a hard nut to crack in terms of breeding them in managed care,” said Alanen. “However, through the efforts at the ACNC, we now know that female Mount Graham red squirrels' cycle through their breeding cycle a few times each spring, which means there are several opportunities each year to successfully breed them rather than just one like we originally thought.”
Currently, the U.S. Fish and Wildlife Service, Arizona Game and Fish Department, Forest Service, Animal and Plant Health Inspection Service, and University of Arizona, as well as the Phoenix and San Diego Zoo, have dedicated resources to manage, monitor, and develop solutions to save this truly unique squirrel.
