I’ve been getting more and more interested in squirrels. Like all animals, their lives are shaped by the seasons, and there’s much to discover if you can find and decipher the signs they leave. In late summer 
squirrels bite off oak twigs to get at the ripening acorns, and the “nip twigs” (minus acorns) can be found scattered under oak trees. The acorn remnants–shell fragments and partly eaten acorn meats–may also be found on the ground or on nearby logs or stumps where a squirrel has a good view of its surroundings while feeding.
In September I found these apparently uneaten acorns, along with cap and shell fragments, scattered on the ground beneath some red oak trees. The acorns were intact, but every one was marred by brown spots. 
This puzzled me at first, so I got out my magnifier and took a closer look. I noticed that there were tiny tunnels in some of the brown spots, and one even had a minute, worm-like insect larvae. I also saw indistinct gouges in a few of the brown spots that looked a lot like tooth marks. Mystery solved! The squirrels were feeding on acorn weevils, often found inside acorns and much richer in calories than the acorns themselves.
We’ve had a very wet fall, 
and fungi have been popping up everywhere. I’ve been surprised to see how fond squirrels are of mushrooms. I’ve repeatedly come across mushrooms which had been plucked from where they had grown, carried to some other spot, and partly or almost completely eaten. Bite marks sometimes showed along the edges, and there were always discarded pieces scattered around–squirrels seem to be sloppy eaters. 
Slugs and snails also seem to love mushrooms, but they simply make broad, shallow gouges in the caps and the mushrooms remain standing where they grew.
When the weather turns colder squirrels give up their summer leaf nests 
and move into more sheltered lodgings, often in hollow trees. Instead of using leaves, they line their nests with fibrous material. The inner bark of this dead branch was stripped off by a squirrel and used to provide warm insulation for its nest. The smoothly denuded wood surfaces and hanging remnants are typical of squirrel work. 
In addition, there are usually a few gouges made by the animal’s incisors somewhere in the debarked area. Dead branches are the most common source of good nest lining material, but the bark of living honeysuckle and other shrubs is a favorite material where they are available.
You may have been wondering which squirrels I’ve been talking about. Actually, I’ve purposely avoided naming them because I’m often not sure. Our mixed forests host both red and gray squirrels, not to mention northern and southern flying squirrels, and it’s often difficult to know which species left a particular sign. I suspect that the oak nip twigs and the weevil feeding were done by gray squirrels, but red squirrels also feed on acorns. I’m pretty sure both red and gray squirrels eat mushrooms, and all of our squirrels line their winter nests with fibrous material. There are some types of sign–certain kinds of marking, and large middens under conifers–that can definitely be attributed to a particular species; more about those in future blogs. Until then, we’ll adopt the wise tracker’s attitude and recognize the limits of our certainty.