young squirrel on pine tree with rose in background

Squirrels in our Backyards

Mammals / Denver, Year-round

The most common squirrel in the Willow Spring Open Space and in our backyards is the Eastern Fox Squirrel. It is not native to this area but has thrived here in our urban forest.

A Bit about Squirrels

Fox Squirrels (Sciurus niger) are in the Order Rodentia, or Rodents. Rodents make up 1/3 of the mammal population on Earth! In addition to squirrels, Rodents include mice, beavers and porcupines. The most common characteristic among rodents is that they have four incisor teeth that are used for gnawing. The incisors grow throughout the animal’s life and are kept to the right length by being worn down by chewing. If they don’t get worn down, they can grow through the animal’s skull!

Fox Squirrels are further classified into the Sciuridae Family. Animals in this Family are primarily diurnal (active in the day), have bushy tails, four toes on the front feet and five on the back. They include chipmunks, marmots, ground squirrels, tree squirrels, flying squirrels and prairie dogs.

Fox Squirrels are recognized by having yellow to brown fur on their backs with lighter orange fur below. Their tail is bushy and they are 10-15 inches long, plus their tail which is another 9-14 inches long. They weigh only 1.25 to 3 pounds. Their ankle joints are very flexible, allowing their feet to rotate 180 degrees and climb down trees head-first.

The Life of Fox Squirrels – What they eat

Fox Squirrels are classified as Tree Squirrels, but spend a lot of time on the ground in search of food. They are omnivores, eating fruit, nuts and buds, along with bird eggs and insects such as moths and beetles. They bury nuts for eating in the winter when the food is more scarce, and sometimes end up planting trees when they don’t eat those nuts they buried. One food source they are especially fond of is from a bird feeder, and they are very adept at getting around all the anti-squirrel measures that people take to keep them away from their bird feeders!

squirrel on bird feeder
Fox squirrel at birdfeeder

Predators of Fox Squirrels

These squirrels are a prey animal, and have to be careful for predators. In addition to being great at climbing trees and leaping up to 15 feet from one to another, they try to confuse predators by running back and forth in different directions, stopping and starting. While this may work well for their animal predators, such as foxes, coyotes and birds of prey such as red-tailed hawks and great horned owls, this doesn’t work out for them as well when trying to avoid cars.

Nests and Raising Young

If you see a big messy nest of leaves and sticks high up in a tree, that is most likely a Fox Squirrel nest, also referred to as a “drey”.

ball of leaves in the limbs of a bare tree
Squirrel Nest

These nests are used for shelter and to raise their offspring. If a Fox Squirrel finds a suitable tree cavity, they also will use that as their nest.

Fox Squirrel mothers generally have 2 litters of 2-5 babies each year, one in the spring and the other in the early summer. Newborn babies are naked and are cared for by their mothers for the first 7-8 weeks. Then, after weaning, they are fully independent at 16 weeks. When the mother has to leave the nest during the first weeks, she will cover the babies with leaves to hide them from predators.

Winter adaptations

Fox Squirrels do not hibernate in the winter. They eat as much as possible in the fall to put on extra fat, and their fur also helps them endure the weather. They also retreat to their nests for warmth at night.

In conclusion…

Although Fox Squirrels are not native to this area, they provide an important link in the food chain. They can be fun to watch as they run up and down trees, and they provide many hours of research for birders trying to keep them out of the bird feeders!

References and Further Reading