Shallow mounds of fresh soil, scattered remains of spiny cactus fruit, and small holes around the base of boulders and shrubs are the first signs to look for. If you are walking in the desert hills or along trails around the neighborhood and find these clues, you may spot one of the three species of ground squirrels that share our big backyard. In the cooler mornings and evenings, a patient observer will almost certainly catch a glimpse of one of these common native rodents in the area.
Most abundant of the three are Round-tailed Ground Squirrels, also known as Spermophilus tereticaudus to mammalogists. The Latin translates to “seed-lover with round tail.” Looking like miniature prairie dogs, just nine inches long including their thin, furry, black-tipped tail, the pale tan squirrels will sit up on their hind legs to survey their territory, then retreat into one of their holes at the slightest threat. Like the prairie dog, these tiny squirrels are also social, living in family colonies of about a dozen. They are also very vocal, peeping and chirping to each other to warn of danger. Their elaborate network of tunnels and chambers may have several dozen entrance holes leading to chambers three feet below the surface. As with all ground squirrels, their ears are small and flattened against their head, an adaptation that helps them to navigate underground more easily.
About twice the size of the Round-tail, and less common at this elevation, is the Rock Squirrel, Spermophilus variegatus. Their fur is a darker “variegated” color, sometimes looking white-spotted or mottled gray. Rather than a round tail, they sport a broad bushy tail like a tree squirrel. By no means limited to rocks, these squirrels are adept climbers and can be seen up in trees and on roofs as well as perching as sentinels on top of rock walls or boulders. When threatened they will make a loud, shrill whistling sound. Unlike the Round-tail, these squirrels are mostly solitary except when mating or raising pups. They are also the most likely to invade your home, being bold enough to scavenge around in a garage or patio for food.
Ammospermophilus harrisii, the Antelope Ground Squirrel, is the third, whose Latin name means “sand and seed-loving, named after Harris.” You’ll easily recognize an Antelope Ground Squirrel by the racing stripes running down their sides, plus a flat furry tail that arches over their backs when they run for cover. These are the most desert-adapted of the three, being the only one that is active year round, even during midday in the summers. To the contrary, Rock squirrels and Round-tails will both be dormant in their dens during the hottest and coldest times of the year, and are rarely seen during midday whenever temperatures hit triple digits. Like the Rock Squirrel, they are solitary unless mating or raising pups. Their warning call is a chattering sound. Of the three, the Antelope is least common around housing areas, and more likely to be seen in more rocky territory of the wild desert.
Although all the ground squirrels are named as “seed lovers,” they are also opportunists that feed on cacti, insects, carrion, bird eggs, roots and green vegetation whenever available. They are extremely well adapted to desert climates, deriving nearly all of their water from the food they eat. Being prey species, they are hunted by coyotes, owls, hawks, snakes, fox, and bobcat. But if they survive the hardships of desert life and are quick enough to evade predators, they can enjoy basking in the morning sun, raise a few litters of pups, and eat seeds for a few seasons.
Since May 2005, I have written a natural history column for a neighborhood newsletter published by Jennifer Moore called "Our Big Backyard: Natural History of the Deem Hills," and since 2010, "A Suburban Naturalist."All of these columns are reproduced here. Deem Hills is a City of Phoenix Desert Preserve located just north of Happy Valley Road in north central Phoenix, and just west of I-17. The Preserve and adjacent hills comprise over 900 acres of open space with several miles of hiking trails. For more perspectives from the Deem Hills and suburban Phoenix, also check out my companion blog, Kat Tracks.
As a naturalist with a special interest in botany and plant ecology, some of my greatest passions are to explore, photograph and write about native plants. If I can spark an awareness or interest in natural history in others along the way, that is my greatest reward.