Mt. Graham red squirrel in a breeding program at the Phoenix Zoo. Photo by Tara Sprankle / Phoenix Zoo

Photo by Tara Sprankle / Phoenix Zoo

PHOENIX - "Al" and "Bob" bound across their cages when Stuart Wells opens the door to their room at the Phoenix Zoo's conservation center.

It's an act of aggression, says Wells, the zoo's director of conservation and science. The Mount Graham red squirrels, isolated atop the Pinaleño Mountains in Southeastern Arizona, are territorial and defensive.

They are also endangered.

The Phoenix Zoo is Noah's Ark for the only two Mount Graham red squirrels in captivity. Large cages once holding ferrets received climbing structures and nesting boxes filled with camel hair and paper to house the squirrels. A black board at the back of one cage separates the two physically and visually.

Al and Bob could be the first incorporated into a pilot breeding program awaiting approval from the U.S. Fish and Wildlife Service.

But the captive breeding efforts won't start immediately. Al and Bob, as you may have guessed, are both males.

Four red squirrels were brought here in July 2011 when officials feared wildfires on the mountain could wipe out the population. The two females died last summer for no apparent reason, Wells said.

In the meantime, field researchers and program planners are learning what they can about the squirrels to determine how to breed the species. Females are in heat only about one day per year and are aggressive toward one another the rest of the time.

"That may take years," said Wells, the squirrels' population manager. "We don't know much about them. They're challenging - I do know that."

Listed as endangered in 1987

Not everyone is sure the Mount Graham red squirrel population can wait that long.

The Fish and Wildlife Service began working on a plan for captive breeding in 2006 and has since had help from the zoo and other agencies, said Marit Alanen, a biologist with the service who is based in Tucson. The plan aims to breed squirrels and release them into the wild as a "buffer" for the natural population, she said.

It could be approved as early as this spring, though it's been stalled before, she said.

Mount Graham red squirrels were first listed as endangered in 1987 based on their declining population. That decade, the University of Arizona supported building telescopes in their habitat on Mount Graham.

The UA is required to maintain a squirrel monitoring program as part of that construction.

Additionally, the Arizona Game and Fish Department, U.S. Forest Service and U.S. Fish and Wildlife Service monitor the population and release an estimate of their numbers each year.

The 2012 population was 214, down slightly from the 2011 estimate of 240, according to a release on the count. The population has settled between 200 and 300 since the late 1990s, it said.

Though the numbers are stable, they are low, said John Koprowski, professor of wildlife conservation and management at the UA and director of the Red Squirrel Research Project.

The effects of the telescopes and roads on the population have been minimal since Koprowski joined the project in 2000, he said.

Instead, population threats have come in the form of low food availability, habitat destruction from fires and insect infestation.

Competition for food

Red squirrels also face competition for the same food supply from the Abert's squirrel.

With so many threats and so few squirrels, one natural disaster could put the population in peril, Koprowski said.

This concern is what led the Fish and Wildlife Service to initiate plans for a captive breeding program as a part of the recovery efforts for the species, Alanen said.

The service enlisted the help of the Phoenix Zoo, which has had success breeding and releasing other local species such as black-footed ferrets, springsnails and Chiricahua leopard frogs.

Several facilities could join the Phoenix Zoo in breeding squirrels, including one in Bloomington, Ill.

"At the time the decision was made, the whole reason it was even suggested is the team felt there was a need there," Alanen said. "There could be a catastrophe up there."

The plan calls for capturing no more than 16 squirrels during the 10-year pilot program, Alanen said. Then a recovery team would determine whether to launch a full breeding program. No more than 10 percent of the squirrel population would be handled during any one year.

Field research will play a role in capturing the squirrels and starting the breeding process, Alanen said. The Fish and Wildlife Service has worked with Koprowski to determine the best practices to include in the proposal.

Koprowski will provide information in areas such as where to capture squirrels as well as the seasonality of mating behaviors, he said.

"You have to time that very well," Koprowski said. "The rest of the year they're very aggressive toward each other."

Those breeding the squirrels will be careful to monitor population genetics to keep the gene pool diverse, Wells said. The wild squirrel population has undergone genetic testing, which will be used in the breeding plan.

The service opened the proposal to public comment from September to October 2010. Seven parties responded with concerns ranging from how capturing squirrels for the program will affect the population to how released squirrels will behave in the wild, Alanen said.

Each comment must receive a response and will be incorporated into a revised plan, she said. Or commenters will receive a response explaining why no changes were made.

Keepers gaining knowledge

The process has been stalled at that stage.

"We get pulled in different directions based on priorities," Alanen said.

The zoo has a limited ability to learn about breeding with its two males, but keepers are gaining knowledge on squirrels in captivity, Wells said.

Staff has worked to determine a diet that keeps the two at their ideal weights. The squirrels have to forage for the food as they would in the wild and have no direct contact with keepers, Wells said.

Wells has created a guide on keeping Mount Graham red squirrels in captivity that includes information such as at what temperatures they can live, how they should be housed and diet. The guide is updated as the zoo learns more about the squirrels.

Still, successful captive breeding could take years. Wells said he hopes a disaster doesn't strike Mount Graham in the meantime.

"It's tenuous," he said. "That's why we're so interested in starting a program."

Brenna Goth is a NASA Space Grant intern. Email: