Population Trends of the Mount Graham Red Squirrel

Population Trends of the Mount Graham Red Squirrel

The Mount Graham Red Squirrel Monitoring Program (RSMP) conducts a quarterly census of the squirrel population within their monitored areas (all areas within 300m of the Mount Graham International Observatory and Access road; and two non-construction, control areas). Biologists visit each midden site, examine it for evidence of red squirrel activity, and observe for extended periods of time to determine the presence of a resident squirrel. Multiple visits are often made to midden sites to verify the residency of a squirrel, and attempt to determine its sex, age, and any natural marks or tags.

Throughout the course of this study slight differences in red squirrel numbers between the construction and non-construction study areas have been observed. However, many natural disturbances such as fire, insect outbreaks, and fluctuations of food resources have caused significant declines in population size of these monitored squirrels. Additional research is, therefore, needed to isolate these factors in order to determine what impacts telescope construction and operation may have on the squirrel population.

The following figure depicts mountain-wide red squirrel population estimates and disturbance events through time. These population estimates are the result of inter-agency censuses conducted by Arizona Game and Fish Department in conjunction with the U. S. Fish and Wildlife Service, the U. S. Forest Service and The University of Arizona. Mountain-wide population estimates are obtained from press releases that follow interagency censuses.


MGRS population timeline 1986 - 2019
Melissa Merrick Mt. Graham red squirrel (T. f. grahamensis) population estimates in the Pinaleño Mountains, Arizona USA 1986 – 2019 relative to disturbance events.


The following graph represents data collected in the RSMP monitored areas only. 



Summer and winter Mt. Graham red squirrel population size by forest community type
University of Arizona Red Squirrel Monitoring Program Summer and winter Mt. Graham red squirrel (Tamiasciurus fremonti grahamensis) populations (including juveniles), by forest community type, June 1989 - December 2019, University of Arizona Red Squirrel Monitoring Program study areas, Pinaleño Mountains, Graham County, Arizona.

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