Abert’s Squirrel, Sciurus aberti
Abert’s squirrel (Sciurus aberti) is a tree squirrel that is native to the North America. It is also known as the tassel-eared squirrel. Its range extends from the Rocky Mountains all the way into Mexico, with large populations appearing in Colorado, Arizona, New Mexico, and the Grand Canyon. Its range is slightly fragmented, with most populations being isolated to the Rocky Mountains, but the introduced populations in the Graham and Santa Catalina mountains of Arizona are stable. There have also been confirmed reports of this squirrel in Spanish Peaks State Wildlife Area, by Mellott and Choate, possibly extending its range by 43 miles.
Abert’s squirrel derives its common name from the American naturalist John James Abert, who was also the leading military officer in the Corps of Topographical Engineers. This squirrel holds nine subspecies, all of which were previously recognized as separate species.
Abert’s squirrel can reach an average body length of 1.9 feet, with a tail length of up to 9.8 inches. The most distinguishing feature of this squirrel is its ear tufts, which can reach a length of up to 1.8 inches. Its long fur is typically grey in color, with a pale or white fur on the underbelly and a visible red stripe running down the back. Individuals that reside in the rocky foothills of Colorado bare black fur all over. If not for these colorations, Abert’s squirrel would look very much like the Eurasian Red Squirrel.
Abert’s squirrel prefers a habitat within ponderosa pine forests, in arid and cool areas of these trees. The squirrels prefer mature trees that can produce more pinecones, which are a main source of food. The average home range of each squirrel varies depending upon its location and the seasons, but studies show that the nest habitats have ponderosa pines with a diameter of twenty inches.
Abert’s squirrels depend heavily on the ponderosa pine for food, shelter, and nests. Summer nests can also be built within Gambel oak and occasionally cottonwood trees. Instead of building nests within the pine trees, these squirrels will build their nests on branches, because they are too large to fit inside the tree.
Most nests, although they vary in size depending upon location, are located in the upper third region of the tree crown. These can be found against trunks, or in dips or boles on top of the branches, as far up as 90 feet. Often times, the crowns in which the nests are placed are supported by “witches brooms”, infestations of the dwarf mistletoe tree. During the winter, a mother and her sub adult baby will share these nests. The nests are built by females Abert’s squirrels, using pine twigs that can reach a diameter of .5 inches and a length of up to 2 inches. These shelters are typically used year round.
Abert’s squirrels are diurnal, but they may be active right before sunrise. The typical mating season may vary upon location, but in central Arizona, mating typically occurs from May 1 to June 1. A study conducted with eight litters showed an average litter size of three to five hairless young. Between three to six weeks, the mother will transport her young to a larger nest. By seven weeks of age, the tail fur has grown in and the ears are held erect. These babies are weaned at ten weeks of age and are fully grown by 16 weeks.
The typical diet of Abert’s squirrel consists of plant materials from the ponderosa pine, including the seeds, buds, cones, and bark. It will also consume soft fungi, bones, carrion, and antlers. These squirrels will choose to eat the seeds of the Mexican pinyon over those of the ponderosa pine if they are available. They have been known to eat the acorns of Gambel oaks as well. These squirrels consume most of their water from the pine materials they eat, but they will drink from standing water like stock ponds or rain puddles.
Because the ponderosa pine only produces cones every three to four years, Abert’s squirrels will begin eating the pine seeds once they start to grow. Each squirrel can consume up to 75 cones per day when available. Between the months of October and November, the seeds will be separated from the cones and stray seeds will be eaten off the ground. During the winter, the inner bark of twigs takes up the majority of their diet and they can eat up to 45 twigs per day.
It is though that the northern goshawk may consume so many Abert’s squirrels that their populations will not grow, as suggested by Reynolds. Other possible common predators include grey foxes, hawks, coyotes, and bobcats, although there are no confirmed reports of this. The mortality rate of these squirrels is thought to be high due to injuries, like broken teeth, and food shortages. Abert’s squirrel appears on the IUCN Red List with a conservation status of “Least Concern”.
Image Caption: Abert’s Squirrel (Sciurus aberti). Credit: NPS/Wikipedia