Tag: white-tail deer

Bark Eaters

For the indigenous peoples of our region bark was a starvation food, but for many animals, bark is a regular, or at least occasional, component of the winter diet. Most of the thickness of a woody plant stem or branch consists of dead wood and bark cells, but the innermost layer of the bark, located between the wood and the outer bark, is made up of living cells. This stratum, known as the cambium, is responsible for the production of new tissues when growth resumes in the spring. It’s no more than a few cells thick, but for both human and animal consumers these living cells are the only part that provides useful nutrition in the winter.

Bark feeders leave conspicuous evidence of their activity, and this evidence is especially obvious in early spring before it gets obscured by plant growth. With careful observation it is usually possible to pinpoint which species the bark eater belonged to. In the photo below you see the results of cottontail rabbits feeding on downed branches of black cherry. The branches were relatively low to the ground, within reach of a rabbit either standing on the ground or supported by the winter snowpack. The rough appearance of the chews is characteristic of rabbit feeding–the bites penetrate to varying depths, often beyond the cambium into the sapwood. Gouges made by the incisors can be seen in several places.

Rabbit chews on staghorn sumac, shown in the next photo, show similar irregularity in the depth of the debarking. Rabbits seem to take in more woody material than they really need to, perhaps because they can make use of it through coprophagy. Rabbits have an intestinal pouch called a caecum in which partially digested material is fermented by beneficial bacteria. The soft stools produced by this process are passed out of the anus and eaten, allowing the animal to absorb more nutrients before expelling the twice-digested material as fecal pellets.

Chews made by squirrels are usually higher above ground level than rabbit chews and don’t show as much irregularity in depth. The staghorn sumac stems in the next photo were fed on by gray squirrels. Young, vigorously growing stems like these have thin bark and are an attractive meal for a hungry squirrel.

A close-up of one of the stems in the preceding photo is shown below.

The debarked patch on the staghorn sumac branch shown in the next photo was about four feet off the ground. This was an older stem with thicker bark, but gray squirrels had no trouble removing it to get at the cambium.

Deer occasionally feed on bark and leave tooth gouges similar to, but larger than those of squirrels. Their debarking is generally found between two and five feet off the ground. Since deer lack upper incisors, they can only access bark by drawing their lower incisors upward. This leaves thin hanging flaps of tissue like those seen on the staghorn sumac stem in the photo below.

Porcupine chews, like the one on beech in the next photo, have a more organized appearance. They can be anywhere from ground level up, but are often seen high on the trunk or upper branches.

Beaver chews, like rabbit chews, are limited to the reach of an animal standing on the ground or on the snowpack. The tooth marks are organized in regular patterns, sometimes in neat rows like those on red maple in the photo below. The upper incisors made the small digs in the bark and the lower incisors created the long grooves below them.

Our smallest bark feeder is the meadow vole. The buckthorn shown in the photo below was fed on by meadow voles working below the level of the snowpack. Tiny tooth marks can be seen at the edges of some of the dark areas. Meadow voles prefer to stay hidden under the snowpack, so their chews are generally located close to the ground.

In the next photo you see debarking by a pileated woodpecker on a big tooth aspen. Woodpecker feeding is often mistaken for mammal chews, but woodpeckers mine dead trees to get at insects, while rabbits, rodents, and deer chew on living trees to access the cambium. Woodpecker feeding can occur at any height, from downed logs on the ground to trunks and branches high in the canopy. The debarked area is textured by the digs and gouges made by a bird beak rather than mammal teeth.

Deer, meadow voles, and squirrels resort to feeding on bark only when other foods aren’t abundant, but for beavers, porcupines, and rabbits bark is a mainstay of the winter diet. Once the growing season begins the choice of foods becomes more diversified, but in winter and early spring the living cells hidden within the branches and twigs of woody plants can make the difference between life and death.

Leafy Disturbances

Leaves: at this time of year the woody plants are bare of leaves, and last summer’s weather-beaten foliage covers the forest floor in all directions. Is there anything we can learn about the lives of animals from this seemingly mute carpet? The answer is a resounding yes! In the photo below we see a well-used deer trail. The dry, undisturbed leaves on either side contrast with the darker, disturbed texture in the trail. Even when it’s compressed, deciduous leaf litter is harder to walk on than pre-existing trails, so deer often create runs between bedding and feeding areas.

It’s not as easy to detect deer tracks if they’re not on well used trails. The next photo shows an individual deer track, orientated toward the right. The hoof pressed down into the leaf litter and the outer rims left curved depressions on the top layer of leaves. But if you just were hiking along, would this print attract your attention? Probably not. To find individual deer prints it helps to study areas where the animals have spread out from obvious trails into feeding or bedding areas.

Fall is mating season for whitetail deer, and back then the males were spending most of their time trying to attract females. Bucks made scrapes on the ground and left their scent at the site by depositing urine in the scrape. They also left their olfactory signature by rubbing their foreheads and faces on overhanging branches. The signs of these mating rituals often last into spring. In the photo below (taken a few weeks ago) you can see a scrape just below an overhanging branch still bearing a few leaves.

A close-up of the scrape has a weathered look but still shows signs of deliberate disturbance.

Deer aren’t the only animals that clear leaves. Turkeys sweep leaves aside as they search for insects and other edible tidbits beneath the leaf litter. In the photo below debris lies on top of the leaves at the bottom and lower right, showing that the turkey stood facing the upper left as it tossed the leaves backward. By using both of its feet the bird created a roughly triangular cleared patch.

But turkey feeding scrapes aren’t always triangular. In the next photo you see one that’s more irregularly shaped. There can be a lot of variation in the shape of the cleared area and the amount of displaced debris.

Buck scrapes and turkey scrapes can be quite similar, but there are ways to tell them apart. First, deer mate exclusively in the fall, so buck scrapes discovered in the spring will show signs of several months of weathering. Turkeys make feeding scrapes in all seasons, so at this time of year they range from fresh to weathered in appearance. Both of the turkey scrapes shown above are relatively recent, while the buck scrape in the preceding photos had been created about five months earlier.

Another difference between deer and turkey scrapes is their distribution. An individual buck usually makes a limited number of scrapes, almost always associated with overhanging branches, in an area he is patrolling. Turkeys usually feed in groups, and they go wherever the eating is good, so turkey scrapes are likely to be more numerous and scattered more irregularly.

Squirrels also disturb leaves. The next image shows a cleared area at the base of a tree. When I found this I wondered if it was the result of frequent use as a take-off spot by squirrels.

To check, I looked at the bark above the cleared spot (shown in the next photo) and saw that the moss and outer bark had indeed been abraded. I’m attributing this to squirrels, the most common tree climbers, but I can’t entirely eliminate the possibility that it was a raccoon. Other climbing animals are unlikely because they are less likely to climb one tree repeatedly.

Like turkeys, squirrels search for buried nuts and insects, especially in the spring when stored food supplies may have run out. Both red and gray squirrels obtain these items by digging small holes. In the next photo you see a dig made by a squirrel. Debris from the hole can be seen below and to the right, so the squirrel must have been facing the upper left as it dug.

Here’s another image of a squirrel dig, this time in a layer of pine needles. If the buried object was a nut or acorn the hole usually retains a firm impression of the object. In the digs shown in both photos the bottoms of the holes were loose and irregularly shaped, so the food items were probably insects.

Deer also dig at leaf litter in search of nuts and acorns. White oak acorns are consumed by many animals and birds, so they disappear soon after they drop. The higher levels of tannins in red oak acorns make them less palatable, so they mostly lie uneaten on the ground until soaking rains leach the tannins out. But once they’re more digestible red oak acorns are sought out by many animals, including deer. Where red oaks are the predominant oak species, areas of churned up leaves like those in the next photo (taken last December) can be found in late fall and winter. You can see fragments of acorn shells and meats the deer dropped as they chewed.

If there’s a heavy, wet snowpack in late winter that compresses the leaves, deer feeding areas may be hard to recognize by the time spring arrives. But after winters with little snow like the one we just had, the signs are evident. A few weeks ago I went back to the area where the photo above was taken to see what it looked like. In the photograph below you can see that the leaves still lie loosely in piles and windrows. There aren’t any acorn fragments to be seen–if the deer weren’t interested enough to gather them up they would have been eaten by other animals like squirrels, mice, raccoons, crows, foxes, or even fishers. You’re not likely to find fresh evidence of deer foraging for acorns because the fall crop has been mostly consumed.

Areas where the leaves were not churned up by deer (or turkeys) look very different. Fall rains and the little snow we did have were enough to flatten autumn’s leaf fall into a smooth-looking mat like the one pictured below.

Some places cleared of leaves are more mysterious . Is this the work of a deer? Or a turkey? Actually, neither.

When you see the same spot in the more distant shot shown below, you’ll see what moved the leaves: water. The close-up above comes from the area in the lower left quadrant of the distance shot below. During a heavy rain, water flowed down the trail on the right and spilled over the edge into the leaves. As the water rushed downhill it made channels in the leaves and moved them into heaps along the edges.

Leaves have stories to tell, and to understand them we need to get familiar with undisturbed leaf litter. Once we begin to pay attention to leaves, and to places that depart from the unaltered baseline, we’ll have a whole new window into the lives of animals.