The main culprit in the squirrel number drop seems to be a die-off of more than 16,000 spruce and fir trees, which produce the squirrel's preferred food--seeds from cones.
"Spruce and fir trees in the higher elevations continue to be decimated by insect infestation," said Genice Froehlich, wildlife staff officer for the Safford Ranger District of the Coronado National Forest.
"We anticipated decreases in activity in the spruce-fir areas, but [squirrel] midden use in the transition and mixed conifer areas also appears to be decreasing," she said.
A June 4-8 survey conducted by biologists from the Forest Service, University of Arizona, U.S. Fish and Wildlife Service and Arizona Game and Fish Department found only 15 percent of the squirrel middens, or homes, in spruce and fir forest were occupied. In mixed conifer forest it was 48 percent occupied, while in transition forest it was 46 percent occupied.
Previous squirrel counts over recent years have been much higher. In fall 1998, 549 squirrels were estimated to be present. That number fell to 528 in fall 1999, then 474 in fall 2000, according to USFS records. The spring 2001 estimate is about 326 squirrels--a number that has not been seen for nearly a decade.
Froehlich has been warning that as the number of insect-killed trees increases, she expected to see lower numbers of red squirrels. In the fall of 1999, Froehlich said, "An increase in the number of spruce trees killed by spruce beetle infestation coupled with a poor spruce cone crop seem to have resulted in a decrease in midden activity in areas with Engelmann spruce trees.
"We've been experiencing some die-off in the spruce forest. As a result, we are seeing drops in squirrel occupancy rate, especially in spruce, that are fairly drastic. As more spruce trees die, the rates of occupancy may decline," Froehlich said nearly two years ago.
That prediction has now come true to a dramatic extent.
"The main thing I want to reiterate," she said recently, "is this infestation is far from over. Maybe 16,000 trees were killed last year. It could be the same number this year."
Froehlich said the options of chemically treating individual trees or selectively cutting them aren't promising.
"The infestation is so widespread, it's pretty useless to do any forest-wide treatment. And stepping up our controlled burning in the spruce and fir forest would not help. It will kill all the live trees if we burn in the spruce and fir," she said.
At present, Coronado National Forest has burned about 75 acres out of 1,100 acres approved for controlled burns. The forest gained approval for burning 1,100 acres over five years from the U.S. Fish and Wildlife Service in October 2000.
OTHER FACTORS causing the drop in squirrel numbers, according to the Forest Service, are loss of habitat caused by the Clark Peak fire in 1996, successive years with poor cone crops, winter snow accumulations that have been absent in past years, construction of an astrophysical facility and a possible shift of squirrel activity to areas lower in elevation on the mountain.
Robin Silver of the Center for Biological Diversity in Tucson blames the population drop on the construction of telescopes on the mountain by the University of Arizona, and a loss of squirrel habitat.
"The squirrels are endangered because of piecemeal loss of habitat. The controllable piecemeal loss to date is the loss of 1,000 trees and interference with squirrel migration by astronomers. Also, fire suppression activities are aimed solely at saving Columbine Cabin. They jeopardize the squirrel," he said.
"The only variable we can control is to make sure habitat destruction is stopped. That means that the telescopes should be removed, along with Columbine Cabin and the Bible Camp, and habitat restoration should be pursued as soon as possible," Silver said.
Buddy Powell of Steward Observatory, which operates the three telescopes now on top of Mount Graham, said squirrel numbers actually increased in the 1990s during the time of major telescope construction.
"We've been on the mountain since 1989, and during the heavy construction, squirrel population went from about 125 to 550. We know well over 1,000 acres are affected by bug infestation. From the LBT, we see massive devastation of the spruce and fir. We're only eight acres--we're just 8/1,000ths of this issue," he said.
"We have a very small footprint on this mountain. The bottom line is, if 1,000 acres were killed by bugs, how much impact did eight acres have?"
JEFF HUMPHREY, A SPOKESMAN for U.S. Fish and Wildlife Service and the agency that oversees the recovery of endangered species, said large die-off of spruce and fir trees and the drop in squirrel numbers have caused the agency to reevaluate its species recovery plan.
"The condition of the forest there is of great concern to us. So we contacted a number of people to see if we can reconvene a recovery team," he said.
Members of the new team will include representatives from the Forest Service, AGF, USFWS and independent specialists in rodents and tree succession.
"I imagine initially they'll do some review of how squirrels can survive on Mount Graham given the present forest conditions. Can they move? Are they moving? Is there enough habitat to maintain them?" he said.
When asked whether captive breeding of squirrels was an option, Humphrey said, "That is an option. Its viability would be studied."
When asked if another option included the removal of the three telescopes now atop the mountain, Humphrey said, "It's something we're not considering right now."
He did point out that the telescope presence "opens the canopy" of the forest and thereby changes the forest microclimate in unpredictable ways.
Humphrey pointed out the die-off of trees and the drop in squirrel numbers may be a part of the natural biological order on Mount Graham.
"There's evidence that die-offs like this have occurred over the millennia, and they have probably had a role in the natural cycle on Mount Graham. We need to assess if this current cycle is something the [squirrel] species can tolerate, like it probably has in the past," he said.
Humphrey also raised a concern about the fire danger from thousands of standing dead trees. Such fires could spread to healthy parts of the forest on Mount Graham. He said his agency and the Forest Service are looking at ways to expedite controlled burns to reduce the fire danger from standing dead timber.