San Juan Mountains Association
This fall, while leading a group of third graders around Junction Creek campground near Durango, we were all enthralled with the bustling activities of Abert's squirrels, getting ready for winter. These small, furry, tree-dwelling animals are fun to learn about and observe.
Abert's squirrels can be grey, reddish, or black on the back, with a white belly. They weigh about two pounds; their head and body are 12 inches long and their tail is nine inches long. Their signature ear tufts are longer in the winter, and may disappear in the summer.
Abert's squirrels are found in Colorado, southeast Utah, and south into New Mexico, Arizona, and Mexico. There are nine subspecies of Abert's squirrels that are associated with different areas. They are also directly associated with ponderosa pine trees. These trees provide them with just about everything they need in terms of food and shelter. They build nests out of small branches that they can weave into a safe place to raise young.
Unlike most squirrels, Abert's squirrels are active all year round. They mate in the spring, anywhere from February to early June, and have a litter of three to four pups about 40 days later. Abert's squirrels do not hibernate or cache their food for the winter (except for mushrooms), so evidence of them can be found throughout that season.
On a simple and complicated level, Abert's squirrels are connected with their ecosystem. Abert's squirrels eat seeds from the pine cones, inner bark, buds, and pollen cones. They will pluck a mature pine cone from a tree, remove the scales, then eat the protein-packed seeds. They eat pine needles and the inner bark of twigs, the latter especially in the winter. Evidence of Abert's squirrels includes seeing the ends of ponderosa pine branches on the ground; this happens when they are getting to that inner bark. They gnaw off the ends of the branches, letting the pine needle ends fall to the ground. They retain the remainder of the branch, removing the outer bark, and eating the “phloem” or inner bark. They then drop the remainder of the twig on the ground. In the summer the squirrels will collect mushrooms, and hang them all over trees to dry. These become winter meals.
When Abert's squirrels eat some buds and shoots of the ponderosa pine, the uneaten part of the twig falls to the ground. This provides food for mule deer. Goshawks are the main predator of Abert's squirrels. Other predators may include bobcats, mountain lions, and coyotes.
Aberts squirrels return to the same ponderosa pine trees year after year, for various possible reasons. Some researchers have found that the trees the squirrels prefer have more sugary sap, as well as more carbohydrates, nitrogen and sodium, and less iron, mercury, and some monoterpenes (toxins).
The squirrels actually help the tree, in addition to using it. Ponderosa pine trees have a mutualistic relationship with mycorrhizal fungi, found in the soil. The fungi extends the reach of the tree's roots, helping it get to more water, phosphate, nitrogen and other nutrients, and the tree provides the fungi with carbohydrates. From late spring to early fall, the squirrels eat the 'fruiting body' of the ectomycorrhizal fungi — the part that shows up above ground for part of the year. This mushroom has spores throughout it, which the fungi use to reproduce. When eaten, the spores survive through the digestive tract of the squirrel, coming out in its scat, and thus being spread throughout the ponderosa pine forest, especially those trees where the squirrels like to hang out. This is an amazing trifecta of a mutualistic relationship — among the Abert's squirrels, ponderosa pine trees, and ectomycorrhizal fungi.
This winter when you are out exploring our beautiful ponderosa forests, take a quiet moment to look around — chances are you'll find evidence of some of our tree-dwelling — and tree-helping — friends around.
Gabi Morey is the Education Outreach Director for San Juan Mountains Association. SJMA is a nonprofit 501(c)(3) dedicated to public land stewardship and education. SJMA partners with the San Juan National Forest, BLM Tres Rios Field Office and Canyons of the Ancients National Monument, BLM, in addition to other organizations in SW Colorado.