Eastern Gray Squirrels Preparing For Winter
Eastern Gray Squirrels (Sciurus carolinensis) eat about two pounds of food per week. Nuts and other seeds are at the top of the list, but fungi, berries, bird eggs and nestlings, tree buds and sap are also consumed. Because they stay active in winter, Eastern Gray Squirrels must store food in the fall in order to survive the colder months, and this food must be viable for the duration of the winter. They are what are called “scatter-hoarders” – they bury each nut separately, not all in one spot. After digging a hole 1-2 inches deep with its front paws, the squirrel places a nut in the hole and forcibly puts it in place by pounding it into the ground with its front incisors. It then fills the hole with soil and covers it with leaves. A combination of memory (experiments found that this works for about 20 minutes) and after that, scent, allows squirrels to relocate a portion of their cached nuts.
Hickory nuts are the food of choice for Eastern Gray Squirrels, in part because they have twice the calories of an average acorn. They also store well over winter, as they don’t germinate until spring. As the accompanying photograph shows, Eastern Gray Squirrels, before burying the nuts (in this case, Shagbark Hickory, Carya ovata), methodically remove the fragrant husks, leaving a pile of small pieces of husk on the ground. It’s likely this practice developed in order to prevent competitors from smelling, digging up and consuming the squirrel’s winter food supply.
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Eastern Gray Squirrels Lining Nests
Congratulations to Wanda Rice, the first Naturally Curious reader to recognize sign made by a squirrel collecting nesting material. Many people thought it might be a porcupine at work, but porcupines, as “hellomolly” pointed out in her comment, do not leave strips of bark hanging, while squirrels do.
In the Mystery Photo, an Eastern Gray Squirrel had been shredding and collecting the thin bark of a Maple Sugar sapling to line its nest with. Gray squirrels nest throughout the year, but nesting activity peaks during their two mating seasons (December -March, and May – July). They build two types of nests – large, round, leafy nests among tree branches (dreys) and cavity nests, the latter being preferred during the colder months. Abandoned woodpeckers nests as well as natural-formed cavities provide additional protection in the winter from predators as well as the elements. (Drey broods are 40 percent less likely to survive than squirrels born in tree cavities — a hole no wider than three or four inches protects them from large predators such as raccoons.) Both types of nests are lined with soft material such as lichen, moss, grass, pine needles and shredded bark.
The effect of a squirrel’s stripping a tree’s bark depends on the extent of the damage. Usually a young tree is chosen due to the thinness of the bark and the ease with which it can be stripped. Although a tree can survive with some of its bark removed, it will die if the damage is too severe or bark is stripped off around the tree’s circumference. Stripped bark not only provides nesting material but the process of stripping the bark exposes the tree’s cambium layer which contains the nutrients and sugars a tree has produced and which squirrels readily consume. (Eastern Gray Squirrel photos by Margaret Barker Clark)
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Eastern Gray Squirrel Diet Preferences
The diet of Eastern Gray Squirrels is extremely varied. Depending on the season, buds, fruit (such as the pictured crabapples being consumed), maple and oak flowers, berries, seeds, fungi, the inner bark of maple and elm, insects, and young birds are eaten. However, nuts are by far the main component, which is reflected in their distribution; the range of Gray Squirrels coincides strikingly with that of oak and hickory forests. Especially during the colder part of the year, nuts, acorns and maple seeds, or samaras, that they have stored for winter consumption are the mainstay of their diet. (Research shows that Gray Squirrels recover 85% of the nuts they store.)
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Eastern Gray Squirrels Swimming
Imagine coming upon a stick floating in a large pond only to discover the “stick” had a head and tail and was making a beeline for the shore. The fact that an Eastern Gray Squirrel (Sciurus carolinensis) had paddled half a mile to get from one shore to the opposite shore of a pond shouldn’t have come as such a surprise, as this rodent has a long history of migratory swimming behavior, but it’s such an incongruous and unexpected event that it made my companion and me initially question our eyesight and then laugh out loud.
Historical reports suggest there have been many massive Eastern Gray Squirrel migrations in the United States, beginning in 1749 in Pennsylvania. Records show the state paid three cents for each squirrel killed; over 640,000 squirrels were turned in for bounty. One migration from Wisconsin in 1842 lasted four weeks and involved a half billion squirrels. Because of the numerous squirrel migrations, John James Audubon was erroneously convinced that the squirrels on the move were a separate species from the Eastern Gray Squirrel and gave them the scientific name Sciurus migratorius. (This proved to be inaccurate.)
During the 1800’s, thousands of squirrels would periodically move en masse across roads, fields and forests, and swim across lakes and rivers (including the Mississippi and Connecticut Rivers) in an effort to disperse. The consensus is that these mass movements were a response to local food conditions. They occurred mostly during the month of September following a year in which there was a large production of food (acorns).
The most recent mass migration of Eastern Gray Squirrels in eastern U.S. occurred in 1968, when a bumper crop of acorns in 1967 was followed with a corresponding bumper crop of young squirrels in 1968. By fall, as the first litter of the year left the nest, there was a severe shortage of food. As a result, massive numbers of acorn-eating squirrels dispersed in search of food.
One Eastern Gray Squirrel swimming across a New Hampshire pond does not a migration make, but it might not be a bad idea to keep an eye out for excessive numbers of paddling squirrels and/or road-killed rodents come September. (Photo by Erin Donahue)
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Gray Squirrels Caching Nuts
Many species of squirrels, including the red squirrel, are “larder hoarders.” Each individual stores its food in one central area that it defends aggressively against invaders. Eastern gray squirrels, however, are “scatter hoarders,” collecting and burying one nut at a time throughout home ranges up to 7 acres in size. It has been estimated that up to 25 percent of the nuts that gray squirrels cache are stolen by other gray squirrels. Researchers have found that gray squirrels engage in “deceptive caching.” Carrying a nut, a squirrel will repeatedly dig a hole and then fill it in, without depositing the nut. They also will cover a spot with leaves, even though they have not buried anything in this location. Where gray squirrel densities are high, the squirrels often keep a cache in its original location for only about three days before moving it to a new location.
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