Linda J. Spielman

Squirrel Nests

As the leaves come down it’s easier to see into the forest canopy, and the summer nests of squirrels become more visible. The photo below shows a gray squirrel nest, a leafy structure located on a supporting branch junction. Also known as dreys, gray squirrel nests are usually located in crotches or branch junctions of deciduous trees. To build a nest in a tree, a squirrel constructs a framework of twigs and stuffs it with leaves, then makes an entrance hole and hollows out the inside of the structure. A lining of soft material such as moss or dry grass is added, and a second opening is made to serve as an emergency exit. Dreys differ from bird nests in being roughly spherical, with an enclosed interior space connected to the outside through small openings. Bird nests also lack the leafy appearance of gray squirrel nests.

Red squirrel nests are similar but are likely to incorporate a variety of materials in the outer layers. They are also more likely to be built in conifers. The next photo shows a red squirrel nest located in a larch tree. Twigs and grasses form the lower part of the nest, and fragments of plastic sheeting cover the upper part.

The nest shown above was easy to see in winter when the larch was leafless, but nests located in evergreen conifers are harder to find. The one in the photo below was tucked up against the trunk of a Norway spruce tree.

Here’s another red squirrel nest which was constructed in the crotch of a Scots pine.

There’s not nearly as much information available on flying squirrel nests, no doubt because flying squirrels are nocturnal and not as easily observed as gray and red squirrels. Mark Elbroch, in Mammal Tracks and Sign, Second Edition, reports that flying squirrel dreys are smaller than red or gray squirrel nests and are made of grasses and other fine materials rather than leaves.

In more southern climes dreys may suffice for winter lodging, but in our area squirrels move into more sheltered accommodations when the weather gets cold. Human structures are used where they are available, but hollow trees are the preferred choice for forest-dwelling squirrels. Nests enclosed in protective walls of wood and lined with insulating materials provide warmth, protection from the weather, and security. But is there any way for us to know which tree houses a nest? It’s not always possible, but there may be clues. The tree in the photo below must have had a good nesting space because it had been marked with a few bites. We recognize the bites visually, but the persistent odor of the resident squirrel’s saliva is more important to other squirrels, signaling that the space is occupied.

Red, gray, and flying squirrels all make winter nests in hollow trees. If the opening is quite small it’s probably not occupied by a gray squirrel, but beyond that, the size of the opening doesn’t tell us much about who the occupant is. I’ve found marked openings in trees where gray squirrels are absent and red squirrels are common, and also in areas where the reverse is true, so I believe that both species create bite marks to claim nest sites.

Bite marks can be sparse, like the ones above, or plentiful, like the artistic creation in the next image. I suspect that the double ring of bites was created because the owner felt threatened by the presence of other squirrels.

Nests in hollow trees continue to be useful well into spring as birthing dens. But although well protected from the elements, they have a drawback: there is usually just one entrance. In the next photo you see some nest lining that was removed from a nest and ended up in a pile on the ground. This would only have happened if a predator had raided the nest and, in the process, pulled the nest lining out. It could have been a fisher, or possibly a raccoon. Both are good climbers and fishers are considered to be specialists in squirrel predation. At any rate, nests in hollow trees are not completely safe.

In addition to clues about predation, the photo above shows us what nest lining looks like. To make this material, squirrels harvest bark and process it into finely divided strands that can be stuffed into tree cavities to provide insulation. The bark usually comes from dead branches, but may also be gathered from living stems of plants such as honeysuckle or white cedar.

The next image shows a dead striped maple branch that was stripped for nest lining. The exposed wood and fibrous remnants may bring to mind a buck rub, but buck rubs differ in several ways. Buck rubs are made on living stems that are more or less upright and have no obstructions that would hinder the approach of a large animal. Rubs are usually limited to one continuous section of the stem and occur at heights between 1 1/2 and 4 feet off the ground. Branches stripped by squirrels have random angles from vertical and could be anywhere from ground level (including fallen branches lying on the ground) to much higher. Bark is usually removed from multiple areas, and there may be a tangle of branches that would make it hard for a deer to reach the debarked sections. And finally, the wood surface of a buck rub shows signs of abrasion, while the wood exposed by squirrel stripping is mostly smooth.

Stripped branches do sometimes have telltale squirrel tooth marks like the ones in the photo below.

If you keep track of weather you’ll notice that cold nights are often followed by new bark stripping. I sometimes imagine a shivering squirrel thinking, “Wow, it was cold last night, I’m going to get more insulation for my nest!” Well, maybe it doesn’t happen exactly like that–sorry about the anthropomorphizing. But it’s clear that squirrels respond to cold with increased harvesting of fibrous bark. And it’s okay to imagine a squirrel sleeping in a cozy, insulated nest in a hollow tree on a cold winter night.

A Family Resemblance

Rodents are the most common mammals on earth, in both number of individuals and number of species. They are also the most diverse, with lifestyles that range from semiaquatic through fossorial (adapted for digging and living mostly underground), terrestrial, arboreal, and even semi-aerial (gliding flight). But don’t let that mind-boggling profusion intimidate you. In our region many of the most common rodents are members of the squirrel family, a group that is remarkably uniform in physical features. Fortunately for the tracker this uniformity extends to track details and track patterns, and familiarity with the key features will aid in the recognition of any member of the group.

In the photo below you see tracks made by a gray squirrel bounding toward the top of the photo. The five-toed rear tracks lie in the upper part of the image, and the four-toed front tracks can be seen in the lower part. Claw marks show as tiny pricks ahead of the toes of both front and rear tracks. Notice that the toe pads of the three middle toes of each hind print are lined up close together, while the inner and outer toes lie farther back and angle to the sides. Behind the toes you can see a C-shaped grouping of middle pads. The front tracks have only four toes, but again the central two point more forward while the outer and inner ones point to the sides. C-shaped arrays of middle pads sit behind the toes of the front prints, and heel pads (there are two on each foot, but it’s hard to tell in this image) are situated behind the middle pads.

Bounding is the most common gait for most members of the squirrel family, and the resulting pattern is another recognizable trait of the group. In the photo above the two rear prints are almost even with each other and are set wider and well ahead of the front ones, which are also nearly even with each other. This positioning may seem odd, but there’s a logical explanation. At each bound the animal lands on its front feet and draws its rear feet forward so they pass outside of its front legs. As the front feet lift off the rear feet touch down–ahead of the spots the front feet just left–and propel the next leap.

The next photo shows a bounding pattern made by a red squirrel, again travelling from bottom to top. There’s a striking similarity to the first image of the gray squirrel tracks, in both overall arrangement and track details. Because the substrate was softer the rear feet of the red squirrel (in the upper part of the frame) sank in deeper–notice that the whole length of each of the three middle toes registered as a narrow groove. Nevertheless the three toes are closer together and oriented more forward than the outer toes, just as they were in the gray squirrel tracks. In the front tracks of the red squirrel (in the lower part of the photo below) the claws show as grooves rather than pricks, but the overall structure is similar to the front tracks in the preceding shot. If you look at the red squirrel’s right front print (at the lower right in the photo below) you can see clear impressions of the two heel pads.

The chipmunk tracks in the next photo (again bounding toward the top) are consistent with the features we saw in the red and gray squirrel prints. In the right rear print (in the upper right quadrant) you can see that the middle toes are closely grouped and the inner and outer toes are angled to the sides. The left front track (in the lower section a little below and to the left of the right front track) shows the four clawed toes, the C-shaped grouping of middle pads, and the two heel pads.

Mud is great, but winter is also fine for seeing squirrel family connections. In the photo below of red squirrel tracks in snow (bounding toward the top, of course) you see the same characteristic features you saw in the mud tracks. As sometimes happens, the heel area of the right rear foot (at the upper right of the photo) registered as a flattened area behind the middle pads. (If you look back at the first photo of the gray squirrel prints you’ll notice that the heel area of the left rear foot also made a slight impression.) There’s a variation in the arrangement of the front tracks, with the right front well behind but the left front farther forward. This kind of foot placement is often seen in squirrels, but is less common than the more four-square pattern.

Flying squirrels possess gliding membranes (the patagium) which extend between the front and rear legs, and because of this the rear feet can’t pass as far ahead of the front feet as they do in red or gray squirrels. In the next photo you see a bounding pattern made by a southern flying squirrel (oriented toward the top) in which the front prints are situated between rather than behind the rear prints. In northern flying squirrel trails the front prints often lie ahead of the rear ones. Another special flying squirrel trait is the thick covering of fur on the undersides of the feet. Because of this flying squirrel prints rarely show the crisp detail found in the tracks of other members of the squirrel family. But even with these differences, flying squirrel tracks will remind you of the tracks of other squirrels.

In the next image you see a bounding pattern made by a woodchuck. If you didn’t realize that woodchucks belong to the squirrel family, the familiar features of their tracks should make that clear. Woodchucks are more likely to walk than bound, and when a woodchuck does bound it usually places its front feet in a staggered pattern rather than even with each other, as in the photo. Nevertheless, the overall arrangement and the track details are consistent with those of its relatives.

To complete the picture for small rodents in the Northeast we need to add a few creatures that don’t strictly belong in the squirrel family but leave distinctly squirrel-like prints. These include white-footed mice, meadow voles, and their allies. I include mouse and vole allies because each one represents a group of closely related species which are difficult to distinguish from tracks alone.

First, let’s look at tracks of the white-footed mouse, shown below in a bounding pattern heading toward the upper right. In spite of its smaller size, the animal made tracks that are uncannily similar to the tracks in the first three photos. If I didn’t tell you that an individual rear print is just half an inch across you’d be hard pressed to tell these tracks from squirrel tracks.

Vole tracks also show striking similarities to the tracks we’ve already discussed–but with a few important differences. In the next photo you see tracks made by a meadow vole bounding from bottom to top. The track sequence, starting at the bottom, is: right rear, right front, left rear, left front. This staggered arrangement is common in vole trails and differs from the more consistent four-square bounding patterns usually seen in white-footed mice and tree squirrels. Voles can leave more regular bounding patterns, but they often move at something between a bound and a lope and their track patterns tend to be more variable. The toe impressions in vole tracks also tend to be more finger-like than the toes of mice. In spite of these differences the tracks of voles will remind you of mouse and squirrel tracks.

This is all well and good, you may say, but if these creatures are so similar to each other, how can I tell them apart? I’ve mentioned a few variations that can be helpful, but often the most useful trait is size. There’s a neat size progression, and although there’s some overlap between adjacent species it’s usually possible to make an identification with a few measurements combined with other clues. There are two dimensions to consider: track width (more reliable than track length) and bounding trail width (measured perpendicular to the direction of travel across the widest part of a bounding pattern). I’ll focus on the big picture rather than giving an exhaustive account of the numbers–detailed measurements can be found in any good tracking guide. White-footed mice and the smaller voles (woodland voles, for example) are the tiniest of the lot, and meadow voles are slightly larger. Chipmunks come next, and southern flying squirrels are slightly larger than chipmunks. Northern flying squirrels outweigh their southern kin, and red squirrels are larger yet. Gray squirrels beat out red squirrels, and woodchucks complete the series. These differences in body size are reflected in differences in track and trail dimensions, so a few measurements are usually sufficient to clinch an ID. Even when the tracks you’re dealing with are in the overlap zone there are usually other clues that can point toward an identification. And when all else fails, it’s okay to say you just can’t be certain. If you treat each situation as a learning experience, you’ll find yourself stumped less and less often.

Bears: Connoisseurs of Rotten Wood

Late summer is upon us, and along with the fruits and nuts that are ripening everywhere, insects are becoming more available. Insects are an important part of the late summer diet for black bears, and the animals seek out insect populations that are abundant and easily obtained. Decaying stumps, rotting logs, and standing dead trees often harbor large numbers of grubs, ants, and other invertebrates. With their highly developed sense of smell, bears can detect these creatures even when they’re hidden deep inside rotting wood. But if they’re protected inside wood, how easy is it for a bear to get at the goodies?

Just check out the photo below, which shows a tree that was ripped apart by a bear. Large pieces of wood lie scattered around, and the inner parts are broken up and exposed. Only a bear would have been powerful enough to pull a tree apart this way. Notice how the fragments were tossed in several different directions and how some lie quite far from the base of the tree.

Logs on the ground also harbor populations of insects. The next photo shows similar signs of bear activity: large fragments tossed to considerable distances.

Stumps may hide the same kinds of food as logs and whole trees, and bears tear into them in the same way. In the next photo you see large pieces of wood that were pulled away from the stump, some tossed impressive distances. Again, this is something that only a bear could accomplish.

A bear wouldn’t exert this kind of effort if there weren’t something really good–and abundant–inside, and very often it’s the fat- and protein-rich larvae of carpenter ants or wood-boring beetles. The holes and galleries you see in the next photo (a close-up of one of the fragments from the tree in the first image) could have been made by either. It’s often difficult to know what was occupying the wood before the bear tore it apart, because everything edible has been eaten and other clues–like frass–have been washed or blown away.

Bears aren’t the only agents that cause trees and logs to come apart. We usually think of woodpecker excavations as occurring on standing trees, but it’s common for birds to open up logs on the ground. Pileated woodpeckers can do quite a job on a log, as shown in the next photo. But notice the differences: there aren’t any really large fragments, and most of the scattered pieces are quite small and close to the log.

Logs can also disintegrate without any help from animals or birds. The log in the next photo fell apart of its own accord. If you look carefully you’ll see that there’s an order to the way the pieces are arranged. The ones that were originally on the surface (one with bark and another with moss) lie at the lower left. A little above those there are chunks that were originally in the interior of the log. With a little imagination you can reassemble the fragments as they were before they fell apart, and picture the way they collapsed from the main part of the log and landed where they did.

Sometimes the goodies lie underneath rather than inside a log. The photo below shows a log section that may have sheltered an ant nest. Again, only a bear could have moved such a massive hunk of wood.

It’s surprisingly uncommon to find claw or bite marks in the wood, but recently I came across an interesting exception. The log in the photo below showed the usual signs of bear work: sizable chunks of wood tossed far from their source. But there were also unmistakable claw marks.

A close-up of the log can be seen in the next photo. What the bear was after must have been in the cavity in the center of the photo, and in the wood above it you can see claw marks. There’s a clear set of five gouges on the right and another less well defined group just to the left. The animal must have stood roughly where the camera was positioned and raked its claws downward. The wood was rather tough, but the bear was able to rip off large sections. I didn’t find holes or galleries in the wood, but there was some finely divided granular material in the cavity, which suggests an ant nest.

Bears open up trees, logs, and stumps during late summer and early fall, when insect populations are highest and grubs and larvae are fat and abundant. The foods they find in rotten wood, along with the calorie-rich fruits and nuts of late summer, allow bears to put on weight and survive winter hibernation. Every time I find a log, tree, or stump that was opened up by a bear I appreciate the animal’s strength and dexterity, and imagine how it relished the tasty (to the bear) items it found inside.

The Marvels and Mysteries of Deer Tracks

When we think of deer tracks what usually comes to mind are heart-shaped prints like the one shown in the photo below. The paired toes together form the overall shape, and the pointed ends of the toes point forward. In tracks like the one in the photo, the ridge that runs front to back between the toes may be as important for identification as the toes themselves. In fact, the tell-tale ridge may still be visible even when most other track details have been destroyed by weathering or melting.

The specialized feet of deer are very different from those of their ancient five-toed ancestors. The two large toes that make up the print in the photo above are analogous to the third and fourth fingers of our hand, but the toe bones (analogous to our finger bones) are highly modified and are enclosed in tough, protective structures. There are two smaller toes, the dewclaws, which are analogous to our index and pinky fingers and sit higher up on the back of the leg. The innermost toe (analogous to our thumb) was completely lost in the course of evolution. You can see the arrangement of the large primary toes and the smaller dewclaws in the next photo of the front feet of a deer.

Deer hooves are superbly adapted for running and jumping. Their keratinaceous outer sheathing combines with resilient internal tissues to cushion the feet against impact. The dewclaws don’t touch the ground most of the time, but with faster movement or on softer surfaces they can make contact to provide more support. In the next photo you see tracks made by a deer moving toward the right on a relatively soft substrate at a slow gallop. There’s a front print on the left and a hind print on the right. In each track the marks made by the dewclaws sit behind the impressions of the large main toes. (You’ll notice that the dewclaws of the front foot are angled to the sides while those of the rear foot are pointed more to the front.) The feet of deer are small relative to the animal’s size and bear more weight per unit area compared to non-hoofed mammals. This is why deer tracks show up on surfaces that are too firm to reveal the traces of most other animals (a serendipitous side-effect for trackers). It’s also why deer tracks are usually deeper than the tracks of animals like coyotes and bobcats, and why deer are generally less stealthy than mammalian predators.

You can see from the photo above that the two large toes are not always held tightly together the way they are in the first image. Sometimes a “four-toed” deer print can take on a bizarre appearance. In the next photo you see a hind track which has a resemblance to the bounding pattern of a squirrel. The tips of the large toes appear rounded because their points pushed downward under the soil surface.

Here’s an image of the front track of a rapidly accelerating deer in which only the marks of the dewclaws and the tips of the large toes registered.

Even when the dewclaws don’t touch the ground the two main toes may be separated, as in the photo below of a hind foot. Deer can exert muscular control over their toes and are able to spread them when they need more support or stability.

Here’s another shot of a rear track, again with the toes separated.

In the next photo you see some deer tracks I found on a seldom used railroad line. The animal had first walked through some mud and then travelled along the railroad track. It stepped carefully on the ties, and wherever it stepped it left muddy impressions. In the photo the direction of travel is from top to bottom, and what you see are the edges of the hooves printed in mud on the wooden ties. There are two tracks partly superimposed, the front print a little ahead of (below) the rear print.

If the tracks in the previous photo are hard to understand, the next image may help. There’s a front track (at the upper left) and a rear print (at the lower right), and the direction of travel is toward the upper left. The firm sandy base prevented the deer’s hooves from sinking in, and the thin covering of loose sand recorded the track details nicely. The outer rims of the hooves show as curved grooves in the sand, but the inner parts of the hooves barely touched the surface.

Tracks like these are sometimes misidentified as bird tracks, so beware! In fact it’s important to always be fully engaged–even with deer tracks–because, as the preceding photos show, they don’t always conform to our expectations. Every once in a while, among all the typical prints, you may find some that are surprising or puzzling. If you spend some time on these, you’ll gain a deeper understanding of deer tracks, both the common ones and the not so common ones.

What Goes In Comes Out

A big part of understanding animal lives is knowing what they eat. There’s lots of general information available in books and other publications, but to understand the dietary habits of the animals in one’s own landscape requires a few steps beyond that. We can observe animals when they’re hunting or feeding, and we can interpret chews, feeding sites, and feeding leftovers. But for many mammals, especially omnivores and carnivores, scat is the best tool. Scat contains the undigestible parts of everything an animal ingests, and it remains long after the creature has left the scene.

For herbivores, plant fibers make up the bulk of eliminations, so their scat has a grainy texture like the rabbit scat shown below. When herbivores eat foods high in water content their scat may be darker and softer, but the fibrous essence can still be seen.

Raccoons are omnivores, and their latrines often contain scats with a variety of contents. In the next photo you see raccoon scats with grape seeds and skins, apple seeds, ant parts, deer hairs, and the amorphous remains of deer flesh. An important safety note: raccoon scat may contain the eggs of a parasite that can infect humans, so it should never be touched with bare hands. To be on the safe side, it’s best to use sticks or other tools to manipulate scat, no matter whose it is.

The photo below shows river otter scat filled with crayfish shell fragments. In locations where fish are the main prey item, fish scales and bones will be the most common contents. In coastal marshes scats with crab shell fragments may predominate, indicating that crabs make up the bulk of the animals’ diet.

For many omnivores and carnivores scat contents vary with the changing seasons. The bear scat shown below was photographed in early May, and it’s made up of the remains of the newly emerging leaves and shoots the bear had been eating. Bears lose weight during hibernation and for many weeks afterwards because the grasses, sedges, and young shoots they must subsist on are energy-poor foods.

It’s only when higher quality edibles become abundant that bears begin to put on the pounds. The bear that left the scat shown in the next illustration had been feasting on black cherries. The summer diet of fruits and berries is often supplemented with insects, and you may find bear scats containing ant or yellowjacket parts.

Scats like that pictured below, full of fragments of acorns and hickory nuts, begin to show up in late summer. The seasonal abundance of acorns, nuts, and fruits, as well as increasing insect populations, provides a crucial, energy dense diet. At this time bears transition into a period of hyperphagia, and spend most of their waking hours seeking food or eating. The fat stores they put on will carry them through their winter hibernation.

The scat of canids reveals that their diets also follow seasonal cycles. Winter and early spring fare is mostly made up of animal prey and carrion. Signs of feeding on deer carcasses start to show up during the fall hunting season and continue through the winter. The coyote scat in the photo below contains deer hair and leg bone fragments. Foxes also feed on deer carcasses, but they aren’t powerful enough to crack large bones to get at the marrow the way coyotes do. Deer killed by hunters (and the carcasses resulting from the vehicle collisions that seem to spike during hunting season) may be preserved well enough in the cold to last through most of the winter. Carcasses of winter-killed deer also provide scavenging opportunities.

The red fox scat shown below (photographed in mid-March) contains the remains of a small rodent that was swallowed whole. There’s a leg bone in the chunk at the lower left, a molar in the piece at the top, and an incisor in the segment at the lower right. The bones are embedded in twisted masses of short hairs. Positioning its scat on the manhole cover was the fox’s way of signaling its presence to other foxes in the area. Small rodents and other small mammals are a winter mainstay for foxes and coyotes.

Like bears, canines graduate to summer foods as they become available. A sure sign that berries are in season are finds like the coyote scat shown below, filled with raspberry seeds. Note that the segments are tubular and blunt-ended rather than tapered like scats made up of animal remains.

As summer progresses, the menu widens. The red fox scat in the next photo (found in early September) contains acorn shells, apple skins, and fragments of field corn kernels.

Some scats lead to surprising discoveries. The next photo shows some gray fox scat containing the remains of a frog. Hollow leg bones are clearly visible, and when I pulled it apart I saw the still articulated bones of a rear foot. It’s a bit unusual to find frog remains in fox scat, but the really surprising thing is that I found this in early December. The weather had been mild, and apparently some frogs had not yet gone underground for the winter.

Food is central to survival, and scat can provide direct information about what animals eat and when they eat it. The many stories scat has to tell can illuminate not just feeding habits, but also interactions among animals, and interactions with the surrounding landscape. Each story adds to our connection with the animals around us.

Muskrats: Life in Two Worlds

Water and land: they pose very different challenges to the creatures that inhabit them. And yet some animals manage to live in both worlds. The muskrat is a semi-aquatic mammal, at home in the water and comfortable (although not as nimble) on land. The dome-shaped lodges made by muskrats (seen in the photo below) resemble beaver houses, but are smaller and are made with non-woody plants instead of the woody material used by beavers. When conditions are suitable muskrats make bank burrows with underwater entrances. Unlike beavers, they don’t build dams, and they prefer quiet or slowly moving water. Aquatic and semi-aquatic plants make up the largest part of a muskrat’s diet, but the animals also spend time on land harvesting non-woody terrestrial plants. They are also known to consume aquatic animals, including clams, mussels, crayfish, frogs, and fish.

A common sign of a resident muskrat is scat, usually found in small collections on rocks and logs that protrude above the water. These deposits announce a animal’s territorial claim to the pond, marsh, or stream where they’re found. The latrine shown in the next photo is on a large rock at the edge of a river, and it’s unusually large. The quantity and the combination of fresh and weathered scat indicate that a muskrat was actively patrolling its stretch of river.

On land muskrats generally move at a walk. In the next image the direction of travel is from left to right, and because of the snow the animal to placed its hind feet directly in the holes made by the front feet on the same side. A tail mark undulates between the tracks.

When the footing is more favorable muskrats use an overstep or indirect register walk. The trail in the next photo goes from upper right to lower left. Pairs of prints form an overall zig-zag pattern, and in each pair the rear track lies ahead of the front. The sequence, starting from the upper right, is right front, right rear, left front, left rear, right front, right rear. If you’ve noticed that the front prints seem smaller than the rear prints, you’re absolutely correct.

The difference in size is easy to see in the next photo. The right front track is on the left, and the right rear is on the right (direction of travel left to right). You can see all five toes in the front print–the tiny innermost toe is a little nub on the upper edge of the print just behind the full-size toe ahead of it. The four large toes of the front track are connected to the middle pad, and behind that there are two bumps that make up the heel pad. If these characteristics remind you of small rodent tracks you’re right on target. Muskrats are indeed rodents, although they have diverged from other rodents in many of their adaptations. In the rear track five toes can be seen, although the innermost toe impression is just the tip (above the other four rear toes and to the right of the third toe on the front print). The middle pad of the rear print made a partial impression at the bases of the toes, and–as is often the case–the heel pad did not touch down at all.

If danger threatens while a muskrat is on land, it hurries toward the safety of the water at a modified bound or lope. In the photo below you see a typical muskrat bounding pattern, with the smaller front tracks ahead of the larger and more widely set rear prints (direction of travel toward the top). The muskrat’s front feet slid forward into the soft mud, so the tips of the toes lie hidden in the muck. The larger rear feet didn’t sink as far and all five toes show clearly. Except for the relative positions of the front and rear tracks, this bounding arrangement is, again, reminiscent of the bounding patterns of many small rodents.

Muskrats possess a feature that is–as far as I know–unique among semi-aquatic animals: the toes of the hind feet are equipped with fringes of stiff hairs. In the next photo you see a left rear track, oriented toward the top. (There’s also part of a left front print to the lower right of the rear print.) The toes of the rear track are slender and finger-like, and the hair fringes make shelf-like impressions around them. These hair fringes add surface area and enhance the muskrat’s swimming ability. The smaller and un-fringed front feet are more suited to grasping and handling objects.

As you explore wetlands you’re likely to see swimming mammals, and you may find it difficult to know which creature you’re observing. There are clues that can help, starting with size. The smallest are water shrews and star-nosed moles. I’ve never seen shrews or moles swimming, so I’ll just point out that their size means they probably won’t be confused for anything but each other. Of the larger mammals, the ones whose tracks and sign we’re likely to find, the smallest is the mink. Minks swim with their entire body visible above the water, from head to furred tail. Their bodies are long and slim, their ears protrude from their heads, and their tails can usually be seen gently swaying from side to side on the surface. Muskrats are heavier than minks but their chunky bodies are about the same length. They swim with their heads and bodies showing above the water. The muskrat’s hairless tail is flattened vertically and can be seen undulating from side-to-side at the surface. The ears are small and don’t protrude from the head.

Next in the size progression (going by weight) is the river otter, with a body length of two to three feet and a powerful, furred tail that tapers from a muscular base to a small tip. Otters often swim with just their heads showing above water, but they may also undulate up and down or make short, playful swerves and dives. Their ears protrude noticeably from their heads. Our largest semi-aquatic mammal is the beaver, with a body length about the same as an otter but weighing up to twice as much. Beavers swim with most of the body and the tail below the water surface, and their ears protrude from their heads.

Muskrats are one of our most common semi-aquatic mammals. You may be fortunate enough to observe one in its watery habitat, or you may instead find evidence of the its presence. Either way, take time to contemplate the muskrat’s place in the panorama of living creatures and the adaptations that make it so successful.

Deer Browse

Signs of spring are all around us, but there are still some interesting discoveries to be made about the past season. Early spring is a perfect time to learn about the winter diet of white-tailed deer. We may think that deer are basically grazers as we see them placidly feeding in fields, like cows and horses. But that would be wrong. Cows, horses–and bison, to include an example of a wild species–are strict grazers and consume grasses, forbs, and other non-woody plants year-round. Deer are browsers rather than grazers. Although they feed on the same kinds of low-growing vegetation as grazers during the growing season, in winter they switch to the twigs, buds, and bark of woody plants. The deer you see in the lead photo (not my shot, but I couldn’t find a good attribution for it) are eating the twigs of a cedar sapling.

Deer do not have upper incisors, so in order to remove a twig they clamp it between their lower incisors and their tough upper palate. A jerk of the head suffices to yank the twig off, enabling it to be macerated by the molars and then swallowed. Rough breaks like those shown on apple in the photo below indicate that deer were feeding on the small twigs.

This contrasts with the sign left by rabbits and hares, which also depend on woody browse for winter food. Rabbits have both upper and lower incisors, and they make sharp, angled cuts like the ones shown in the next photo of multiflora rose.

The browsing preferences of deer vary in different regions. Some of their favorites in the northeast are sugar maple, ash, dogwood, striped maple, northern white cedar, and hemlock. In the next photo you see a sugar maple branch that was browsed by deer. The animals are not equipped to chew on larger branches, so they limit their browsing to the small twigs and buds at the branch tips. In mature forests these only become available if trees or large branches fall, which is exactly what happened in this case.

Hungry deer will eat everything they can reach, and unrelenting feeding often leaves browse lines like the one on northern white cedar in the photo below. This doesn’t affect the overall health of the stand, but browsing can have adverse effects on the growth of smaller trees.

The ash seedlings in the next photo show the excessive lateral branching patterns that result from heavy browsing. During each growing season the young trees form new twigs and buds, but each winter the new growth is eaten by hungry deer. The stunted trees are never able to outgrow the reach of the deer and eventually die.

Deer found a hemlock sapling at the edge of a field, and you see the result in the next photo. It’s hard to see the hemlock against the background because so many of the small twigs have been eaten, but if you follow the main stem up from the bottom center of the photo you’ll see how much foliage is missing.

Overbrowsing makes a difference in the appearance of forests. In the next photo you see a woodland that has been heavily impacted by winter deer feeding. The lack of understory trees makes it easier to walk through this kind of forest, and its cleaner appearance may be more appealing. But this forest is in trouble.

In the next photo you see a much healthier woodland. The spaces between the large trees are filled with young and medium-sized saplings, and these are the ones that are ready to fill gaps when larger trees die or fall.

Without a multi-aged understory, forests have limited ability to regenerate. When large trees die, there are no young trees ready to fill in the gaps. It’s true that there are seeds in the soil that will germinate quickly once openings are formed, but the delay in regrowth may allow invasive species to get a foothold. Signs of deer browsing tell us much more than the mere presence of hungry animals. There are larger lessons to be learned, and nature is ready to share them if we are willing to pay attention.

Squirrel Marking

Some animal communication is just for the moment, gone as soon as it is created, and some is more permanent. Whether it’s a patch of earth pawed by a deer, a scat deposit carefully positioned by a fox, or a twist of grass left by an otter, messages left in physical media can convey information long after the author has left the area. Squirrels are especially adept at this type of messaging, and their medium of choice is something they are intimately acquainted with–wood. Tree trunks, branches, roots–all can serve as bulletin boards for intra-species communication. One of the best times to observe squirrel marks is early spring, after the snow is gone but before new leaves limit our view through the forest.

The photo below shows an opening into the trunk of a large red maple. Hollow trees provide critical winter shelter, and this one must have been prime real estate because the hole has been bitten around the edges by a squirrel. Gray, red, and flying squirrels (of both sexes) use their incisors to declare ownership of desirable nesting spaces. Theoretically the sizes of the gouges should tell us which species did the marking, but the hole was about thirty feet up, and it’s hard to measure tiny things like tooth marks when you’re that far away.

The creature claiming possession of the tree in the next photo is easier to determine. Gray squirrels, primarily males, make vertical marks called stripes to assert territorial claims. They seem to prefer rough-barked trees like the white oak pictured in the photo, and the stripes are generally found on large trunks between 2 and 6 feet above the ground. I’ve also seen gray squirrel stripes on red oaks, chestnut oaks, hickories, and tulip trees. After marking, a squirrel may rub its cheek on the bitten area to leave its scent. You can see from the varying degrees of weathering that this tree has been marked repeatedly over several years.

Red squirrels also have distinctive ways of creating messages, and one of the easiest to find is the branch marking associated with conifer middens. Middens are accumulations of discarded cone scales and cores found below habitual feeding perches. The photo below shows a midden at the base of a Norway spruce. Most conifers, with the exception of some pines, tend to retain lower branches for years after they have died, and these provide perfect feeding perches. The oversized cones (up to 8 inches long) produced by Norway spruces are prized by red squirrels, and the middens came become quite large.

If you examine the branches above a midden you’ll probably find bite marks like the ones shown in the next photo. The image shows a Norway spruce branch which extends horizontally about four feet up the trunk. The upper surface of the branch is adorned by numerous bite marks. You can see the midden (out of focus) on the ground below the branch.

Red squirrels also make marks at or near ground level. In the photo below you see a Norway spruce root which has crossed over and been lifted over the years by the swelling root crown of a neighboring tree. This tree was part of a plantation that dated from the 1960s, and the trees were close enough together that horizontally spreading roots often passed close to the bases of neighboring trees. This also happens in other conifers when they grow in crowded stands, and the small lateral roots have thinner bark than the trunk and the larger roots.

A closer look, shown in the next photo, shows that a red squirrel has bitten through the bark of the lateral root. The light colored gouges are recent marks and the whitish ones are older, probably made the previous year and covered with dried resin.

Norway spruce plantations were established throughout the east during the Depression and also later in the 20th century. With their large crops of oversized cones, stands of Norway spruce are preferred habitats for red squirrels and are great places to investigate red squirrel marking. Other conifers were also used for reforestation projects, and if they support resident red squirrels you’ll probably find evidence in the form of marking and middens. Both branch marking and root marking are the animals’ way of defending their underground larders of winter food.

Squirrels also use their incisors for purposes other than marking, such as debarking trees to get at the living cells of the cambium. The photo below shows a staghorn sumac that was fed on by a gray squirrel. I found this a few years ago in early March, and the color of the exposed wood indicated that it had been done not long before. Late winter and early spring can be a time of scarcity; stored food supplies may be exhausted and squirrels may be forced to turn to foods which are less nutritious or harder to access. I’ve occasionally found similar cambium feeding by squirrels on sugar maples.

Squirrels, both red and gray, also tap trees when the sap flows in spring. The animals choose vigorous trees, and bites are made in living, thin-barked branches by anchoring the upper incisors and drawing up the lower ones. This creates what Sue Morse calls a d0t-dash pattern. Two fresh bites on a sugar maple branch are shown below, and above them there’s an older bite. Interestingly, the sap is not consumed immediately, but is allowed to dry. Once the water has evaporated the squirrel returns to lick up the crystallized sugar.

When we find a mark made by a squirrel, we can infer something about the availability of food or the presence of a desirable nesting site, but for other squirrels there’s much more involved. The associated cheek rub or saliva deposit is unique to the individual and carries information about its sex, health status, and possibly other characteristics. Even though receiving these messages is beyond our abilities, I enjoy finding squirrel marks and imagining the messages they convey to their neighbors.

Gray Fox Affairs

It’s been a strange winter. In my neck of the woods we had some significant snow early in the season, but no big storms since then. Temperatures have been up and down (more up than down), and with all the melting, the snow we do have has consolidated into a dense, icy layer. Much of the time the conditions have been terrible for tracking, but every once in a while something wonderful has happened: warmth and liquid precipitation have been followed by dropping temperatures and a change from rain to snow. When this happens, snow that falls while the air is still relatively warm becomes bonded to the crust. As the temperature drops and additional snow falls, it forms a soft layer on top. The result is a non-slip and easily navigable surface that is a perfect medium for recording tracks.

A few days ago I encountered just such conditions: an icy base covered by a thin layer of soft snow. I was in an extensive natural area, and both the forest road I was following and the surrounding landscape offered beautiful tracking conditions. Animals of all sorts had been moving easily over the snow, and there were tracks everywhere. I found myself following the trail of a gray fox. The animal went for quite a distance at an easy trot, but then it did something that was quite puzzling.

The photo below shows the fox trail as it goes from upper left to lower right. (You can also see a coyote trail to the right of the fox trail, and a mountain bike trail to the right of that.) As it entered the frame the fox was walking (the first three tracks at the upper left). In the next section (between the last walking step and the edge of the tree shadow) the pattern was very different, and following that the trail looks unlike either of the previous sections. I wanted to know what was going on and why the middle section looked so different.

In a situation like this the first thing to do is identify each track. The zig-zag of the walking section helps us to tell right and left, and the fact that the front foot is larger than the hind foot distinguishes front from rear. The next photo shows a gray fox front print on the left and a gray fox rear print on the right. You can see the difference in overall size and also the difference in the sizes of the middle pads.

The photo below shows just the puzzling middle section, and if you compare photos you’ll see that the front and rear in the photo above are actually the first two tracks in the middle section. It’s pretty clear that the first four prints in the photo below are left front, left rear, right front, right rear. After that it gets harder. The track just above the right rear is smaller than the one to its right, so those two prints must be left hind, left front. Three tracks from the right side come next, and it looks to me like the sequence is right rear, right front, right rear. The final two before the tree shadow are the left front and the left rear, and at the edge of the tree shadow there’s a right front with a right rear partially superimposed on it.

In the next photo I’ve added labels showing my take on right/left and front/rear. If we start at the beginning of the whole sequence, the animal was trotting (those tracks aren’t seen in the photos) and then slowed down to a walk (the first three tracks in the distance shot). The next section shows that the fox slowed even more to an overstep walk (the first four prints in the photo below), then slowed even more to an understep walk. There’s an extra right hind that’s puzzling, but I’m guessing the fox just repositioned its right hind foot. Then the overstep walk reappears after which the fox picked up the trot (the two impressions at the lower right in the first photo). Notice that the step lengths in the overstep part are shorter than the regular walk steps that preceeded them, and the step lengths in the understep part are shorter yet.

That analysis was rather involved, but it leads to a picture of what the fox actually did. As it trotted along something it detected made it slow down, first to a walk and then almost but not quite to a standstill. It was probably sniffing and listening intently as it moved very slowly. Once the animal concluded that it was okay to move on, it resumed its journey at a trot. It’s impossible, without more evidence, to know what caused the fox to react the way it did. It may have been a threat, but it could also have been something that interested it for a different reason. It is, after all, mating season for wild canines.

And the fox I was following was definitely tuned in to mating season. Farther on I found a spot (shown in the next photo) where the animal had detoured to urinate on a small spruce branch. If you look in the center of the frame you’ll see a squiggle of urine that runs horizontally from the upper edge of the spruce branch. Because the urine wasn’t squirted out the side of the tracks we know this was a female. She would have lifter one hind leg forward and supported herself on the other hind leg (plus two front legs) as she urinated. The relative depths of the tracks tell us that the supporting rear foot was the left. Its track is in the prominent double impression above and to the left of the urine.

I’ll never know what made the gray fox slow down and leave the pattern discussed in the beginning of this article. It could have been a threat–there was certainly a coyote in the neighborhood, or it could have been the mountain biker. A fisher (whose tracks I also found on that day) would have made the gray fox nervous. And there were red fox trails as well. But the trail shown in the photos above doesn’t suggest alarm so much as cautious interest. The fox didn’t change direction but just continued on. Was it another gray fox, one she was familiar with, or one she had mated with in a previous year? We have a small part of the whole story, and we can only speculate about the rest, but it’s fascinating just as it is.

Mouse Maneuvers

The mouse–not most people’s favorite creature, to put it mildly. Certainly the house mouse can be a serious pest, but wild mice are different creatures altogether. To start with, they are more attractive than the drab house mouse, as you can see from the portrait of a white-footed mouse which heads this post. The white-footed mouse is one of two species which inhabit the northeast, the other being the deer mouse. They are closely related (both belong in the genus Peromyscus) and are so similar they can’t be distinguished from tracks or sign. Habitat may indicate which one we’re dealing with, but from the tracker’s perspective it’s not really important, since they have similar characteristics and behaviors. White-footed mice prefer deciduous and mixed forests at low and moderate elevations. The trails shown below were most likely made by deer mice, which are more common in boreal and high elevation forests.

Both deer and white-footed mice are hunted by just about every predator in our region, so they stay hidden whenever they can. In warm months they find safety within woody debris, shrubs, blowdowns, rocks, log piles, and sometimes human structures. In winter, snow usually provides ample cover. Mice are able to tunnel through snow if it’s not too dense, and deep snow actually contributes to their survival. Within a deep snowpack the temperature is highest at ground level and decreases toward the surface. The temperature gradient causes ice crystals in the lower levels to sublimate and recrystallize at higher levels, leaving spaces where small animals can find safety and warmth. Hollows at tree bases, among rock outcrops, and under downed logs and branches allow mice to move between the surface and the lower regions (the subnivean zone). That’s why the trails in the photo above radiate from the base of the tree at the upper edge of the photo.

The next photo shows a steep, snow-covered embankment at the edge of a groomed snowmobile trail. A mouse (it could have been either a white-footed or a deer mouse) bounded from the lower left across the packed snowmobile trail toward the slope. The mouse turned to the right and then went under a slight overhang where it found (or dug) a tunnel leading to safety in the deeper snow bordering the snowmobile trail.

Look under the log in the next photo and you’ll see mouse trails. Notice how the mouse trails run into (or out of–or both) the cavity at the upper left, a mouse-sized hole at the lower right, and unseen openings under the lower part of the log. As long as these openings are maintained, mice can move easily between the snow surface and the subnivean realm. The log also provides protection from aerial predators.

In soft snow mouse trails on the surface often lead to holes that connect to tunnels deeper in the snow.

Both deer and white-footed mice store nuts and seeds in cavities in logs, standing trees, and rock piles. Once winter comes any space protected by deep snow makes a good feeding area. The midden of black cherry seeds in the next photo shows where a mouse fed beneath the snowpack at the base of a tree. The neat round holes are reliable indicators of mouse feeding.

Mice use logs as travel routes, but we only see evidence of this when a light covering of snow coats the log surfaces. In the photo below you see a jumble of mouse tracks, a few of which show toes clearly enough to reveal the direction of travel. There’s a rear print at the lower left that points toward the left, and you can see a few front tracks near the upper edge of the snow with toes pointing toward the right.

There are other small mammals, voles and shrews in particular, whose trails can be confusingly similar to those of deer and white-footed mice, especially when they are bounding. But the bounds of voles and shrews are less regular and have more variable foot placement than the bounds of mice. Voles and shrews also use a greater variety of gaits than mice, including walks, trots, bounds, and lopes. Voles especially are likely to make frequent gait transitions, and often use a perplexing gait sometimes described as a shuffle. Mice can walk but it’s rare, and I’ve never seen evidence of a mouse trotting, shuffling, or loping.

Deer and white-footed mice are relatively long-legged and athletic, and they sometimes make long leaps. Voles and shrews, with their chunkier bodies and shorter legs, can’t jump nearly as far. So if you find a trail with leaps like those in the photo below, you can confidently assign it to a mouse rather than a vole or shrew. The tail marks are another clue. Mice have tails as long or longer than their body length. Both the short-tailed shrew and the woodland vole, the two species most likely to be confused with deer and white-footed mice, have very short tails and wouldn’t leave long tail marks like the ones in the photo.

The white-footed mouse trails in the next photo show the typical consistency of pattern and leap length, but the one on the left demands a second look. It begins at the bottom, a little to the right of center, goes upward for a few leaps, and then takes a hard turn to the left. After a few more leaps the trail circles back to the right and proceeds toward the top of the photo where there’s a fallen branch sticking out of the snow (just outside the frame). Each time it turned the bounding mouse flung its tail to the outside for balance, leaving conspicuous tail marks. There’s a pile of snow that was kicked toward the rear where the mouse turned left, and where the trail curves back toward the right the landing/takeoff depressions are deeper. These observations suggest extreme bursts of energy.

We’ll never know for sure, but the most likely explanation is that a threat spooked the mouse. There’s no sign of an actual attack, so the mouse evidently survived, but it must have been alarmed by something. Deer and white-footed mice, along with other small rodents, are in constant danger of predation, and we sometimes find evidence of a successful hunt (see my post for March 1, 2022). But most of the time mouse trails tell us they survived to live another day.