Rock squirrels are rarely sighted in Evergreen

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By Sylvia Brockner

It was shortly after we moved to Colorado that my late husband and I were birding one morning in Red Rocks Park, and we saw our first rock squirrel.

Rock squirrels are the biggest of all the many ground-squirrel clan, and despite the fact that they are ground squirrels, they are quite capable of climbing over rocks and boulders and even well into trees as if they thought they were tree squirrels.

Red Rocks Park is typical of the type of habitat they prefer in this area, so I didn’t realize at the time that seeing this squirrel was such a special occasion. In the intervening 45 years, I have seen this big squirrel on only two other occasions. This is why I think of them as being rare instead of as abundant as they are listed in most of the literature.

Rock squirrels are nearly as large as the Abert’s squirrel but not anywhere near as graceful or elegant as this beautiful tree squirrel. Rock squirrels have the longest tail of any of the ground squirrels. It is nearly as long as the head and body and is fully covered with short hair, giving it a bushy appearance rather than the plume-like appearance of the tree squirrel’s.

In color, they are mostly gray-flecked with dark gray or black. This gives them a mottled appearance. In some areas, the flecking is heavier over the upper back, head and shoulders, making the rear appear almost black. They are rather large-headed, short-necked and blunt-nosed compared with the tree squirrels, and therefore appear less graceful.

Rock squirrels are found on rocky hillsides, in rim-rock canyon country, talus slopes and riparian woodlands, but rocks or rock outcroppings are an essential part of their habitat. They are adaptable to human development and are increasingly found in rock outcroppings within cultivated and urban areas. While they traditionally nested in burrows below rock piles, they have adapted to using piles of automobile tires in junkyards, riprap construction along streams or even beneath a wood rat’s pile of debris.

Rock squirrels make a main burrow beneath a protective pile of rocks, with side tunnels and chambers that are used as storage chambers, toilets, etc. The nest is an enlargement along the main tunnel, lined with shredded bark and other soft plant material. They have three to nine young, with an average of five, and may have two litters per year.

Rock squirrels eat a large variety of food from blossoms and buds to fresh greens, fruits and seeds, especially acorns, many insects and the flesh of nesting birds and small animals. The two rock squirrels that I saw at Red Rocks were in different locations in the spring. They were both high in the treetops, eating the sweet, swelling buds of the cottonwood trees. They probably tasted pretty good after a long winter surviving on dry acorns.

They have cheek pouches in which they can carry food to store, and they do store winter supplies. However, they can be seen out foraging on pleasant spring-like winter days, an indication that they do not hibernate in a deep winter sleep but probably sleep intermittently when the weather is bad. No one knows what goes on in the burrow for sure.

The only rock squirrel I have seen locally lived in a rock pile on the southeast corner of the Evergreen golf course. This large pile of rocks looked like it had been dumped just off the course in the rough, perhaps just as a place to store them for future use. At any rate, the male used the topmost rock as his lookout, and they had a nest burrow beneath the pile for several years.

Further south and in Mexico, they are actually active all winter, and in extremely hot summer weather, they aestivate to escape the heat. When cooler fall weather comes, they become active again.

Rock squirrels are apparently susceptible to bubonic plague. They have fleas, as many wild animals do, which carry the disease and spread it. Statistics from human cases of bubonic plague suggest that about 40 percent of the cases have been traced to rock squirrels.

So, as interesting as they are, you don’t want to encourage them in your backyard, especially if you have small children or dogs.