With only about 240 Mount Graham red squirrels left in the wild, the species’ population is running dangerously low. Once thought to be extinct, the squirrels — identified by their small bodies and narrow heads — are now the focus of a one-and-only Mount Graham red squirrel breeding program being developed at the Phoenix Zoo.
Specially equipped with staffing and resources, the zoo’s Conservation Center hopes to one day provide squirrels for release into newly developed habitats, or into existing areas where there no longer are active squirrel middens. Stuart Wells, director of conservation science at the zoo, answered a few questions about the disappearing species and the challenges the program faces.
Tell us about the Mount Graham red squirrel.
The Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis) has been isolated within the upper regions of the Pinaleño Mountains of Southeastern Arizona for an estimated 10,000 years following the receding of glacial bodies, causing an island effect. This is the only location of this subspecies in the world. The squirrel was listed as endangered in 1987 because of its limited distribution, reduction of habitat and threats to existing habitat. These listing factors were caused by anthropogenic (human-caused) factors, as well as by naturally occurring conditions. The population estimates have remained at or below 300 for the past 10 years.
Why did the Phoenix Zoo decide to start a breeding program for the squirrel?
In 2006, the zoo answered a call from the U.S. Fish and Wildlife Service to help develop a pilot breeding program. Their concern was raised due to the prevalence of drought conditions, and the fact that no viable ex situ (off-site) reproductive efforts had ever been achieved.
In 2011, while we were in the process of obtaining the breeding permit, Mount Graham was experiencing the worst drought since the last wildfire. The Fish and Wildlife Service asked us to hold an emergency-action population of squirrels, at least until the threat of wildfire had abated. We took in four squirrels at that time and began collecting information necessary to develop basic care standards and housing requirements.
Walk us through the efforts at the Phoenix Zoo to help maintain the population.
Currently, we house two adult male Mount Graham red squirrels. They are both considered to be in excellent health, although we have had some challenges at keeping them within goal weight. This appears to be a function of metabolic changes associated with the season, rather than a problem with dietary intake. We have developed a system for regulating their dietary intake based upon seasonal metabolic changes to maintain ideal body weight.
The two females that we were holding died suddenly within a week of one another in July of 2012. We believe that stress related to visual proximity to the other squirrels may have contributed.
The males are housed in separate enclosures, and a visual barrier is in place to reduce stress. Each enclosure is also equipped with two nesting boxes. The squirrels typically choose one box to sleep in, and one box is used to cache food and other items, such as walnut shells, chewed pine cones, bones, etc., thus acting as a midden.
The squirrels are provided with artificial light on a timed schedule consistent with seasonal changes, as well as natural light via windows located at the facility. The building where the squirrels are housed is maintained at 65 degrees year-round to keep them acclimated to the average temperatures occurring in their natural habitat.
What challenges does the program face?
It is challenging to develop an ex situ breeding program for this species. Both genders are highly territorial and defend the boundaries of their midden from other squirrels. The only time this territoriality is relaxed is when the female is receptive for breeding. Field studies have determined that the window of receptivity for females is only a few hours for one day of the year. At the breeding center, we must determine when that window is accessible, and for how long. If introductions are conducted at the wrong time, the squirrels could inflict serious injury to each other as a result of their territoriality.
We use a variety of tools to help us determine this window. We will use behavioral observations and observable changes in physiology. Zoo professionals have a particular expertise in developing ex situ animal husbandry protocols as a result of being charged to maintain animals, outside of their natural habitats. The Conservation Center focuses on developing breeding programs for species that are intended to be returned to the wild. This adds another layer of complication because it is important to maintain the behavioral and sociological components necessary for predator avoidance and breeding.
We welcome these challenges and look forward to developing a successful breeding program for the Mount Graham red squirrel.
— Kirsten Kraklio