Eastern Gray Squirrel

Scientific Name	Sciurus carolinensis
Survival Strategy	Active All Winter
Conservation Status	Least Concern

Phenology

Spring
In late March or early April, the spring litter of 2-6 young eastern gray squirrels is born in a tree cavity. The young will nurse until they are 50 days old.

Summer
After mating in June, a second litter is born in a leaf nest (drey) in late July or early August. The second litter will stay with the female over the winter.

Fall
The most critical tasks for squirrels in the fall are forage for calorie-dense nuts to cache for winter and build a layer of fat (brown adipose tissue) to burn as fuel in the winter.

Winter
Gray squirrels do not hibernate and are active all winter except during extreme weather when they remain in a drey or den. Mating for the spring litter happens in February.

Behavior

Food Caching
Eastern gray squirrels scatter-hoards nuts in the fall to prepare for winter. Sometimes they will pretend to bury a nut they are holding to trick other squirrels. This “slight of paw” trick is called “deceptive caching.” Using their acute sense of smell, they can relocate the nuts through snow nearly a foot deep. Squirrels will not recover over half of the buried nuts, and some of those will sprout new tree seedlings.

Dens and Dreys
Eastern gray squirrels will spend their nights and cold days in a tree cavity that serves as a den or in a nest of leaves 30 feet up a tree. They will often repurpose woodpecker holes to use as dens. Squirrels preferred dens for over-wintering and when brooding newborn squirrels. Several adult gray squirrels will share a shelter to conserve heat in colder months.

Nests, also known as dreys, are found in large trees’ upper branches and are made of twigs and leaves. Dreys can be a fire hazard due to squirrels’ propensity for chewing on electrical wires. Females often move their litters between dens and leaf nests in response to weather, predators, or parasite infestations.

Physiology

Brown Fat
Eastern gray squirrels build a layer of brown fat, also called brown adipose tissue, to help generate heat in the winter. Brown fat has more mitochondria than white fat, and these mitochondria act like fat-burning stoves which produce heat quickly.

Head-first Descent
The eastern gray squirrel is one of the few mammals that can descend a tree head-first. Using its flexible ankles joints, the squirrel can turn its hind feet backward, allowing its claws to grip the tree bark. House cats cannot do this, and it’s why they have difficulty climbing down from a tree.

Fur Color
The eastern gray squirrel commonly occurs in several colors. While gray is the predominant color, some local populations are black (melanistic). Less common are squirrel populations that are white (leucistic). Studies indicate that black-morph animals have 18% less heat loss. This advantage may explain why black-morph squirrels are more common in the northern part of their range.

Diet
Eastern gray squirrels are opportunistic foragers. Most of their diet is “mast” (the fruits, seeds, and nuts of trees and shrubs). These omnivores will also eat crops such as corn and wheat, mushrooms, and insects. They will even eat bird eggs and nestlings.

Lifespan and Mortality
The average life span of an adult eastern gray squirrel is six years. Only 25% of gray squirrels survive their first year.

Predators
Common predators of gray squirrels include hawks, owls, weasels, skunks, red foxes, and humans. Occasionally a squirrel crossing a stream may be taken by freshwater fish such as largemouth bass.

Climate Vulnerability
There are no known vulnerabilities due to climate change at this time.

Never stop learning
First Nations: The Ojibwe word for squirrel is “misajidamoo.”

Invasive Species: In 1876, a landowner in England released a pair of gray squirrels brought from America. Today there are over 2.7 million grey squirrels in the UK, pushing the native European Red Squirrel to near extinction. Gray Squirrels carry the Squirrelpox virus, which is highly contagious to red squirrels. While the gray squirrels have an immunity, this virus is fatal to red squirrels.

References

The Ojibwe People’s Dictionary: Squirrel https://ojibwe.lib.umn.edu/main-entry/misajidamoo-na

University Of Richmond. “Researchers Tackle The Nutty Truth On Acorns And Squirrels.” ScienceDaily. ScienceDaily, 26 November 1998. www.sciencedaily.com/releases/1998/11/981126102802.htm

The Scatter Hoarders | Forest Society https://forestsociety.org/something-wild/scatter-hoarders

Caching for where and what: evidence for a mnemonic strategy in a scatter-hoarder https://royalsocietypublishing.org/doi/full/10.1098/rsos.170958

Squirrels Actually Organize Their Nut Hoard — Here’s Why https://animals.howstuffworks.com/mammals/squirrels-really-organize-nuts.htm

100 of the World’s Worst Invasive Alien Species http://www.iucngisd.org/gisd/100_worst.php

Lawniczak, M. 2002. “Sciurus carolinensis” (On-line), Animal Diversity Web. Accessed December 05, 2021 at https://animaldiversity.org/accounts/Sciurus_carolinensis/

Squirrel nests: A night in a drey, Illustration, and text by Patterson Clark, Washington Post, December 11, 2012 https://www.washingtonpost.com/wp-srv/special/metro/urban-jungle/pages/121211.html