The Natural History of the Mount Graham Red Squirrel (MGRS)
Geographical distribution of the genus Tamiasciurus in the western U.S.
The Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis) is a subspecies of the North American red squirrel (Tamiasciurus hudsonicus). The geographical distribution of the North American red squirrel ranges from Alaska, the Yukon, the Northwest Territories, and Quebec southward as far as the Rocky Mountains of New Mexico and Arizona in the west and the Appalachian Mountains of South Carolina in the east. The Mount Graham red squirrel, however, is found only in the Pinaleño Mountains of Graham County, Southeastern Arizona.
With the exception of the flying squirrel, North American red squirrels are the smallest species of tree squirrel in North America. The squirrel measures about 30 cm (approx. 12 inches) from the nose to the tip of the tail and weighs about 225g (approx. 8 ounces). The fur on the back and sides of the red squirrel is brownish-red and the underparts are white with a black stripe separating the two colors. The ear tufts and the limbs are also brownish-red. They have a prominent white eye ring and the tail is brownish-red above and grey with white flecks below.
While the Mt Graham red squirrel subspecies exhibits only slight phenotypic differences (slightly smaller body size and slightly narrower skull) than other red squirrels found in North America, genetic evidence does support the distinction of this subspecies (Sullivan and Yates. 1994. Storm over a Mountain Island. University of Arizona Press, Tuson, AZ).
Red squirrels are diurnal (active during the day) although they may occasionally be active during the night. Activity patterns are strongly influenced by weather patterns; high winds, rain, snow, and low temperatures reduce activity. Red squirrels do not hibernate during the winter months and most activity during this time of year occurs during mid-day hours when temperatures are highest. In summer the squirrels are most active during early morning and late afternoon hours, and in the spring and fall activity levels are equally distributed throughout the daylight hours.
Red squirrels are highly territorial and will vigorously defend the area surrounding their hoard of food by using territorial vocalizations and by chasing intruders away. They not only attempt to keep red squirrels and other competitors at bay, but also exhibit territorial defense behaviors against predator species. The most common territorial behavior is a vocalization called a chatter (or rattle) call. This vocalization serves to announce the presence of an individual to its neighbors, warning them to stay away and avoid costly aggressive encounters.
Common Red Squirrel Vocalizations
|chatter or rattle||territorial defense, announce presence, signature call for individual recognition|
|bark or chirp||Alarm call, indicate presence of predator|
|screech||used alone or with chatter in defense|
|growl||aggressive defense, used during chases and fights|
|squeak||indicates agitation, often precedes chirps|
|buzz||mating, by male approaching female|
Chatter calls are often used: when a squirrel first emerges from its nest, when it returns to its territory, after caching food or feeding, and upon sighting an intruder. Barks are most often given in long series, sometimes lasting for several minutes up to an hour. Squeaks are given in response to a potential threat and increase in intensity if the threat does not diminish. They often progress into barking sessions. Growls are most commonly heard during chases and fights over territories or females. Squirrels caught in live traps will also growl when approached. The squeak and buzz calls are the first calls developed by juveniles and are used to call to their mother.
Watch a red squirrel mating chase with buzz calls