A red squirrel. 

Courtesy of George Andrejko, Arizona Game and Fish Department

The endangered Mount Graham red squirrel's population is down to an estimated 35 due to a 48,000-acre fire that burned the mountain from top to bottom over the summer, authorities say.

A census of the squirrels showed a significant decrease from the 252 squirrels that were estimated to live on the mountain in 2016, said a news release from the U.S. Fish and Wildlife Service. The squirrel census, conducted in mid-September, found evidence of fire activity in 95 percent of the surveyed locations, with 80 percent of the locations showing at least some habitat loss.

Forty-four percent of the surveyed areas were completely burned, according to the survey conducted jointly by the wildlife service, the Arizona Game and Fish Department, the Coronado National Forest, the Arizona Center for Nature Conservation working with the Phoenix Zoo, and the University of Arizona.

The 48,000-acre fire was ignited by lightning on June 7, in an old burn scar remaining from the 2004 Nuttall Fire on the mountain, according to the federal, InciWeb information system . It burned in steep, rugged terrain on Mount Graham's slopes, in elevations ranging from 4,000 feet to the mountaintop at over 10,000 feet.

"It's at the point of being very concerning. It's very scary that the numbers are that low," said Jeff Humphrey, a wildlife service spokesman in Phoenix.

At the same time, Humphrey and Arizona Game and Fish official Tim Snow said it's possible that this survey missed some squirrels who had dispersed into peripheral habitat — outside the area usually surveyed — due to the fire.

Squirrels aren't actually counted in the census, they noted. Squirrel middens, areas of vegetation where squirrels store their cones and other food resources for the winter, are surveyed as surrogates for the actual squirrels, they said. Evidence of activity at the middens is used to estimate their population size, said Tim Snow, a Game and Fish wildlife specialist.

"This year, the forest has experienced a particularly challenging fire season, with 79 fires burning over 125,000 acres,” said Coronado National Forest Supervisor Kerwin Dewberry in the news release. “Several fires covered large portions of the mountain ranges we manage, including the Frye Fire."

The Mount Graham red squirrel is one of 25 subspecies of the red squirrel known to exist in North America. It was listed as endangered in 1987. Mount Graham red squirrels live only in the upper elevation conifer forests of the Pinaleño Mountains and feed primarily on conifer seeds. This subspecies is highly territorial and has lower reproductive rates than red squirrels in other locations.

A number of measures are under consideration to try to stabilize or upgrade red squirrel populations on the mountain, Humphrey said. Funding is being sought for addressing impacts to red squirrels from competition by the non-native Abert's squirrel, for creating artificial middens and providing some cones in them so they have food through the wintertime, he said.

Funding is also being sought to be able to use satellite imagery to look underneath tree canopy cover and see how much needle cover exists for the squirrel,  Humphrey said.

But Robin Silver, an Arizona environmentalist who has been fighting authorities for decades over squirrel protection, said the real fix for the squirrel would involve removal of the University of Arizona's telescopes, some high-elevation cabins and a Bible camp from the mountain to allow recovery of the squirrel's habitat.

Removing those structures "would allow the mountain's high elevation to grow back," said Silver, conservation chair for the Tucson-based Center for Biological Diversity.