When most of us think of squirrels, we probably think of tree squirrels. But the fact is that not all squirrels live in trees. Minnesota is home to a passel of different kinds of squirrels. From chipmunks and woodchucks (ground squirrels) to red squirrels and gray squirrels (tree squirrels), the chances are good that one or more species lives near you.

First, squirrels are rodents. A common characteristic shared by all rodents includes a single pair of incisors, both above and below. These incisors are ever-growing and the reason why rodents must constantly gnaw on wood and other objects. If they didn't chew, their incisors would become unusable. Gnawing helps hone the edges of their chisel-like teeth.

Secondly, squirrels belong to the family Sciuridae. Members of this family include flying squirrels and other tree squirrels, and ground squirrels such as Franklin's ground squirrels, chipmunks, and thirteen-lined ground squirrels. In all, Minnesota has 11 species of sciurids scampering below, on, and above ground.

Nonetheless, with all the squirrels and squirrel-like critters that we Minnesotans have the opportunity to observe, when one thinks of squirrels most would agree that what we think of are those bushy tailed, tree loving varieties that are notorious birdseed robbers.

Occurring throughout most of Minnesota, gray squirrels are one of our most common tree squirrels. Typically gray in color, the gray squirrel is sometimes black. I remember that the woodlands of my childhood in Otter Tail County were filled with large numbers of gray squirrels that included a surprising proportion of black squirrels. Though some people believe that a black squirrel is a different species of squirrel, black squirrels are simply black phases of gray squirrels.

Squirrels are intelligent, agile, and curious mammals. And for those of us who feed wild birds and have tried to devise ways to keep the furry critters out of our birdfeeders, they can also be downright maddening. I have watched gray squirrels and their larger cousins, fox squirrels, and the smaller yet feistier red squirrels, raid my feeders time and time again. A few winters ago I counted as many as 15 gray squirrels and one red squirrel - all at once - hogging the feeders and filling their bellies with my expensive black-oil sunflower seed.

Aside from the obvious differences between the two groups of squirrels - ground squirrels versus tree squirrels - the primary difference is that one group of squirrels hibernates while the other group does not. Species of ground squirrels, for example, such as woodchucks, chipmunks, and Franklin's and Richardson's ground squirrels, all retreat to burrows underground to hibernate.

Meanwhile, the tree squirrels - gray, red, fox, and Minnesota's two species of flying squirrels, the southern and northern flying squirrels - are active throughout the year. Generally, the only times that tree squirrels are inactive are during moments of rest and during severe weather (northern flying squirrels are known to huddle together in tree cavities or bird houses to keep warm, sometimes as many as a dozen or more individuals!). Otherwise, tree squirrels are constantly busy looking for food, hiding food, stealing food, or eating food.

Contrary to a bird lover's belief, squirrels (chipmunks included), eat more than just birdseed. In fact, they spend a lot more time in the woods searching for and eating natural foods than they do stuffing themselves full at our birdfeeders (though it's sometimes hard to believe when you watch squirrels putting on layers of fat because of your protein-rich sunflower seeds and suet treats).

As such, squirrels, in order to survive, depend on mushrooms, fungus, nuts, seeds of all kinds including from spruce and pine cones, fruits and flowers, buds and catkins, inner bark from trees and shrubs, leaves of all types, green grass and other broad-leaf greens, and will also lick with relish the oozing sweet sap that often drips from surface gashes or from holes drilled by yellow-bellied sapsuckers on maple and birch trees. Squirrels also eat insects, eggs, and, believe it or not, young birds.

In a story that I've written about before, I once observed this shocking behavior many years ago. When I was a boy on the farm, I was alerted to a loud ruckus coming from a pair of blue jays flying in the oak treetops next to our house. I watched the pair of jays chasing a red squirrel through the canopies of several large oak trees.

The birds were calling wildly as they tried in vain to get the squirrel to drop a young blue jay from its jaws. Evidently, the red squirrel had just raided the blue jays' nest, stole a chick, and escaped into a tree cavity with its prey. I've also witnessed chipmunks steal bluebird chicks from bird houses and I've seen evidence of Richardson ground squirrels and gray and red squirrels raiding ducks nests (on-the-ground nests and nests inside wood duck houses) to steal, eat, and cache the eggs.

Nevertheless, squirrels are indeed a fascinating group of mammals. Save for the nocturnal flying squirrel, most members of the squirrel family are daytime creatures and are usually very visible for us to watch as they go about their activities.

From the graceful leaps of tree squirrels high in the branches of trees, to docile chipmunks feeding and stuffing their cheeks on our porches, to the curious postures of woodchucks standing on lookout from safe vantages in the fields, squirrels of many types and many sizes are sure to delight as we get out and enjoy the great outdoors.

BLANE KLEMEK is a Minnesota DNR wildlife manager. He can be reached at bklemek@yahoo.com