by Jay Watson, Co-Executive Director, New Jersey Conservation Foundation
If you’re like many New Jerseyans, you probably haven’t given much thought to squirrels, except maybe wondering how to keep them out of your birdfeeders. They’re so common in every New Jersey community – rural, suburban and urban – that a lot of people don’t give them a second glance.
But these cute, charismatic critters do have a fan base, especially in Princeton, where squirrels with unusual all-black coloring are the unofficial mascot of Princeton University. (The official college mascot, the tiger, is certainly more fearsome … though a team called the Black Squirrels would be cool!)
And if you’re a fan of oak trees and forests, you should also be a fan of squirrels, since they play an important role in helping spread oaks by carrying and burying acorns away from the parent trees.
There are even scientists who study squirrels and their behaviors. In case you’re wondering, the science of studying squirrels is called “sciuridology,” and one of the nation’s prominent sciuridologists is Dr. Karen Munroe of Baldwin Wallace University in Ohio.
In a recent podcast, Munroe shared her love for squirrels and discussed their lives and behaviors with host Alie Ward, whose show explores the various “ologies” of science. Squirrels, she noted, are found everywhere in the world except Antarctica, with a total of 289 species globally. Chipmunks are a close cousin.
In New Jersey, our most common squirrel is the Eastern gray squirrel. Eastern grays live in deciduous forests, where they feed on acorns and other tree nuts, including walnuts and hickories. But they’re equally at home in suburbia, and in urban parks and street trees.
Princeton’s famous black squirrels are actually Eastern gray squirrels with a gene mutation that affects their coloration. These “melanistic” populations are also found in several other places in the United States and Canada. Biologists speculate that their darker fur may give them two advantages: absorbing more of the sun’s heat to help them survive winter’s cold, and making them more visible to drivers when crossing roads, and thus less likely to get hit by cars.
The black morph of Eastern gray squirrels is totally natural and nothing new. As Princeton University professor Henry Horn has pointed out, Dutch explorer David de Vries described in his 1655 journals “squirrels as black as coal” in the landscapes of what is now called New Jersey.
Gray squirrels are “scatter hoarders,” and will hide food everywhere within their feeding range of about seven acres. In addition to collecting tree nuts, they’ll gather mushrooms and other fungi to dry and place in their nests to help keep them nourished over the winter.
According to Munroe, squirrels instinctively know which acorn species are most perishable. For example, acorns from white oak trees germinate in the fall, so squirrels will consume them before red oak acorns, which germinate in the spring. Squirrels don’t remember where they’ve buried all of their caches, so plenty of acorns survive to sprout new trees.
Research has shown that acorns handled by squirrels have a better chance of germinating than acorns left on the ground where they have fallen, said Munroe. Interestingly, even acorns that are partly nibbled by squirrels can successfully sprout.
Acorns aren’t necessarily squirrels’ favorite food, though. The tannins in acorns make them bitter, so squirrels will go after tastier nuts when they’re available. “Why would you bother eating an acorn when you can eat an almond or a walnut or a peanut?” Munroe asked.
Squirrels don’t hibernate in winter, but go into a “torpor.” This state has been described as “hibernation light” — a deep sleep with a very slow metabolic rate to conserve energy. Squirrels spend most of their winter days in a torpor, but may be active for a few hours at midday when temperatures are the warmest.
During their months of torpor, squirrels spend most of their time in their nests, known as drays. These globe-shaped structures in high tree branches are built for maximum protection from the cold, with twigs on the outside, an insulating layer of leaves in the middle, and a cozy inner layer of soft moss and fur. Groups of squirrels, often families, will huddle together for warmth. According to Munroe, squirrels build multiple drays within their territory, so they don’t necessarily sleep in the same place every night!
As their name indicates, Eastern gray squirrels are native to the eastern United States and Canada. But Munroe notes that they have been introduced to other parts of North America and even Europe, where they’re considered invasive.
In addition to Eastern gray squirrels, New Jersey’s squirrels include American red squirrels, which are smaller than grays and a rusty brown in color; and Southern flying squirrels, whose loose folds of skin between their front and rear legs form a parachute that allows them to glide from branch to branch. This state we’re in may also have smaller populations of Northern flying squirrels and fox squirrels.
Seeing a squirrel in your yard or neighborhood park may not be as much of a thrill as spotting a coyote, fox or bobcat, but they’re part of nature and valuable to our ecosystems. “We really do have squirrels to thank for most of our trees and mature hardwood forests,” says Munroe.
They are entertaining little acrobats that are just trying to make it through the winter. Look around at the beautiful oak trees in your community and think of the diverse habitat they provide for all sorts of insects and birds. You might give your squirrels a break this winter at your birdfeeder!
To learn more about squirrels, listen to Munroe and Ward’s sciuridology podcast, at www.alieward.com/ologies/sciuridology. The website includes helpful links to many squirrel-related topics.