August 17, 2005
Red Squirrel Population Survey
Here is interesting population survey information provided via Arizona Game and Fish Department News Release.
The Mount Graham red squirrel, Tamiascurus hudsonicus grahamensis is an isolated subspecies found only in the coniferous forests on the Pinaleno Mountains of southeastern Arizona. This limited distribution, combined with a small population and loss of habitat, has made the Mount Graham red squirrel vulnerable to extinction. In response to concerns about the precarious status of the Mount Graham red squirrel, the U.S. Fish and Wildlife Service listed it as an endangered species in June 1987.
Every spring and fall, biologists from the Arizona Game and Fish Department, USDA Forest Service, U.S. Fish and Wildlife Service, and University of Arizona survey the red squirrel population. "We actually visit randomly chosen middens, or cone scale piles," explains Tim Snow, biologist for the Tucson office of the Arizona Game and Fish Department. "We look for recent activity such as new cone scales, fresh digging, and stored cones." Because red squirrels defend territories around these middens, biologists can estimate the population size from the percentage of middens showing recent activity.
Since 1991, inter-agency cooperators have conducted semi-annual surveys using this methodology, once each in the spring and fall. While this spring’s results represent the lowest population estimate since 1991, biologists remain optimistic that Mount Graham red squirrels can rebound from these low numbers. Small mammal populations tend to rebound if given favorable conditions. The recent reductions experienced by Mount Graham red squirrels are most likely related to habitat losses caused by insects, fire, and drought. If and when Arizona receives above average precipitation, such as the case in 1998-99, the Mount Graham red squirrel population is also likely to spike.
More detailed graph below: