Colorado has 19 species of squirrel*, in every corner of the state, though no single species lives everywhere. Each has its own ecosystem where it thrives, and our diverse state has many ecosystems!
But what, exactly, is a squirrel? Aside from being one of the most charming words in the English language and my dad’s nickname for me, they are members of the family Sciuridae, rodents who stand up on their hind legs and are frequently social. Marmots, chipmunks, and prairie dogs are also in this family, but we are going to talk about them in other places, so we’ll just focus on squirrels here.
The little guy I drew below is the Golden-Mantled Ground Squirrel, often mistaken for a chipmunk but lacking stripes on its head. They live in a wide variety of habitats, from lower elevations to the timberline, and hibernate in the winter. They live in rockier areas.
The Richardson’s ground squirrel, also known as the Wyoming ground squirrel, is similar but without a striped fur pattern. They live above 6000 feet in elevation in small colonies and hibernate much of the year, emerging in April and heading back underground in early autumn.
The Thirteen-lined ground squirrel is more solitary than others; it lives in small burrows it digs for itself and can be seen late into autumn, and lives in grasslands, mostly in the eastern part of the state.
The Spotted ground squirrel is small and solitary; it is also one of the few mainly herbivorous squirrels (though it will eat insects). They burrow to make tunnels in which to store their food, shelter, and hibernate. Like many squirrels, they enjoy time outside to sun bathe and groom.
The Rock squirrel is the largest ground squirrel in Colorado. Surprise surprise, they live in rocky areas, and also love to climb trees.
White-tailed antelope squirrels live throughout the southwestern USA and into the Baja region of Mexico. They have a large home range, frequently ranging about four acres in a day.
The Red squirrel is also known as the pine squirrel or the chickaree; they are energetic and you can see them often running around, chittering noisily, on the bark and branches of coniferous trees. Interestingly, they do not hibernate. Instead, they store caches of seeds in hollows and holes in the ground. Seeds they do not eat often grow into new evergreen trees.
Albert’s squirrels are distinctive because of their huge ear tufts (and they are sometimes known as tassel-eared squirrels). The color grades from dark in northern Colorado to light in southern Colorado. They live in ponderosa pine forests specifically between 5000-8000 feet in elevation and are only found in Colorado, New Mexico, Wyoming, and Arizona. They are one of my favorite squirrels!
Fox squirrels are large and live primarily in eastern Colorado (they are one of the most common squirrels found in North America east of the Rocky Mountains). In Denver, if you see a squirrel in a park, chances are you are seeing a Fox squirrel – they produce litters twice a year, so breed quickly, and are a species that seems to get along well with humans, enjoying our trash and anyone they can convince to leave out food for them. They are also invasive species to Europe and generally tough for predators to kill (though my dog Nori did manage to kill a particularly dumb one in a very traumatic moment for me in the front yard). This is because they can leap up to fifteen feet and are extremely fast movers and climbers.
Finally, the northern flying squirrel, our newest known squirrel, is fascinatingly different from our other squirrels. For one thing, they are nocturnal. They are from the only genus of flying squirrels in North America, although like all flying squirrels, they are actually gliding using a patagium, a membranous body part, rather than truly flying. The Wikipedia page for them has a great description of their flying mechanism:
“From atop trees, flying squirrels can initiate glides from a running start or from a stationary position by bringing their limbs under the body, retracting their heads, and then propelling themselves off the tree. It is believed that they use triangulation to estimate the distance of the landing as they often lean out and pivot from side to side before jumping. Once in the air, they form an "X" with their limbs, causing their membrane to stretch into a square-like shape and glide down at angles of 30 to 40 degrees. They maneuver with great efficiency in the air, making 90 degree turns around obstacles if needed. Just before reaching a tree, they raise their flattened tails, which abruptly changes their trajectory upwards, and point all of their limbs forward to create a parachute effect with the membrane to reduce the shock of landing.”
* We actually only knew of 18 until recently, however there have now been multiple credible sightings of the northern flying squirrel.