I just love squirrels! You won’t hear many bird nuts like me professing a love for these four legged, bird food robbing bandits. But I am not afraid to admit it.
I enjoy all squirrels but in particular I really enjoy the tree squirrels. All squirrels are broken into two groups—tree squirrels and ground squirrels. For example, the Eastern Gray Squirrel and Fox Squirrel are types of tree squirrels while Chipmunks and Woodchucks are types of ground squirrels.
Tree squirrels are mammals that belong to the order Rodentia or more commonly known as the rodents. There are over 1,600 species in this group which constitutes one third of the 4,500 species of mammals living on earth today. In other words, one in three mammals walking this earth is a type of rodent.
Looking at the fossil record, tree squirrels appear to have originated in North America and subsequently spread to Eurasia, Africa and South America. The morphology of squirrels hasn’t changed much over the past 5 million years. In fact, squirrels have changed so little over this time that most authorities refer to tree squirrels as living fossils.
Currently there are 26 species of tree squirrels in the genus Sciurus, with 3 species found in Eurasia and the remainder found in North and South America. The reason for their success is their ability to eat energy rich seeds and nuts and live in trees where other mammalian predators find it hard to go.
So what makes a rodent a rodent? Scientist look at the skull and teeth to classify mammals. Squirrels lack canine teeth. The canines are the sharp pointed teeth located between the incisors and the molars or cheek teeth. The incisors of a squirrel or any other rodent for that matter are strong prominent teeth with a chiseled edge on the inner surface that equips the animal with tremendous gnawing ability. Like other rodents the incisors of a squirrel are open rooted and grow continuously through its life. Gnawing on thick shelled nuts and other hard surfaces keep the incisors from growing too long. An incisor that grows unchecked, called a malocclusion, can eventually pierce the skull and kill the animal.
The jaws of a squirrel are amazingly strong and powerful. Combine the jaw strength with razor sharp incisors and you have a nut cracking and seed eating machine that will stop at nothing feed itself. One of the things I find fascinating about tree squirrels is their inability to digest cellulose. Cellulose is the chief component of green plants. Cellulose is a polysaccharide comprising up to 90 percent of a plant. Most herbivores (animals that only eat plants) require symbiotic organisms (usually bacteria) to aid in the digestion of cellulose, whereas many other species, including squirrels, are unable to digest cellulose. In other words they cannot live on green plants and must restrict their diet to the energy rich seeds and nuts.
Let me just stop right here for a moment and digress just a bit. Many people believe that if they see an animal such as a squirrel or deer eat something in the wild, it must be safe for people to eat. Nothing could be further from the truth. For example, both squirrels and deer have been known to eat deadly Amanita mushrooms without any ill effect. If you or I were to eat one of these mushrooms you would not survive. Simple as that.
Now back to the squirrels. Tree squirrels are well adapted to a life in the trees. This is called an arboreal lifestyle. All tree squirrels have extremely strong legs and elongated toes or digits, each equipped with a very sharp recurved claw. In addition their hind legs and feet can rotate 180 degrees, allowing squirrels to scamper down trees headfirst and hang from limbs to reach nuts for food and leaves for their nests.
By far the tail of a tree squirrel is its most distinguishing feature. It is a multi-functioning appendage that aids in balance when scampering and jumping around on thin branches in the tree tops while at the same time helps to regulate heat loss and is also used as a flag or signal when communicating with other squirrels.
In general tree squirrels have excellent eyesight. Aside from the primates, such as apes and monkeys, tree squirrels are one of the few mammals that can see in color. The position of their eyes is also very important. Set wide apart on either side of the head, tree squirrels posse an extremely wide field of view. Anyone who has tried sneaking up on a squirrel knows what I mean.
Although tree squirrels are mostly diurnal (active during the day) tree squirrels possess extra light gathering cells, called cones, in their eyes which allow them to see in very low light of dawn and dusk. Excellent eyesight allows them to keep watch for predators. Now can you see why I like squirrels so much? Until next time…