Category: animal tracking

Bringing Home Dinner

When we come upon a site where a predator killed a prey animal, we’re able to see in detail the interaction between hunter and hunted. But finding such a site is a rare. It’s more common to find the trail of a successful hunter carrying its prey, and this also makes for fascinating study. To understand such a trail we must pick out the crucial evidence from the other disturbances that occur in animal trails. Let’s start with a fairly straightforward example.

In the photo below you see a trail made by a fisher loping from left to right. There are three typical fisher track groups, each group a place where the fisher landed and then took off. Above each track group you can see a curving gouge in the snow made by something the fisher was carrying. But what exactly was being carried? Could it have been a stick? Not likely, based on the length of the trail involved (it went on for quite a distance) and the consistency of the patterns. There’s also the fact that the marks are curved, suggesting that the item being carried was swinging slightly. (If you visit a place where dogs have been playing with sticks you’ll see how different it looks when a stick is being carried.) The predator would have been gripping the body of its prize, and something that extended to the side would have touched the snow at each landing. The curving marks are actually made up of two parallel lines, and these lines seem too widely separated to be claw marks from a dangling foot. Their size and positioning do seem about right for the tips of wing feathers, suggesting it was a bird. If it was a bird it couldn’t have been large, since it only touched the snow at the low points in the fisher’s bounding gait. A turkey would be much too big, and even a grouse would probably have left more traces in the snow. Perhaps it was something the size of a blue jay or a junco.

A short-tailed weasel bounding from upper left to lower right made the trail in the next photo. The trail consists of paired track impressions, a common pattern for small mustelids. To the left of each set of weasel prints there’s a thin, slightly curved line in the snow. There’s also a shorter and wider mark just ahead of the weasel tracks. The thin lines are the right size for a tail, and the wider depressions could have been a foot. Given the small size of a short-tailed weasel, it’s likely that the predator was carrying something equally small. A white-footed mouse seems unlikely, because its long tail would have made a longer stroke in the snow. My guess is either a meadow vole or a woodland vole.

The next photo shows the tracks of a fisher loping from right to left, and just below the tracks you see a wide groove. Below that groove you can see several lighter lines. These finer marks aren’t completely parallel with the deeper groove, so the deep groove and the fine lines must have come from separate body parts. The wider groove seems too deep and even to be something as light as a feather–was it a tail or perhaps a thickly furred foot? The finer lines could be the marks of dragging claws. This example is less clear than the two preceding ones, but I’m inclined to think the prey item was a mammal, perhaps a rabbit.

Now to some examples of marks that we often find in animal trails that don’t indicate dragging parts of a prey animal. In the next photo you see the trail of a long-tailed weasel bounding from bottom to top. There are grooves behind each landing spot, but they weren’t made by something being carried; the marks were made by the animal’s tail. Each time the weasel took off for the next bound its body sank into the snow, and the tail left a tapered groove. Tail marks are always connected to body impressions rather than being off to the side of the tracks as they are in the three preceding photos.

Here’s another example of potentially confusing disturbances that are not indicative of something being carried. The next photo shows the trail of a fisher walking from the lower right to the upper left. The fisher dragged the tips of its feet through the snow with each step. Notice that the drag marks are within the trail rather than to the side, and each drag mark extends completely or partially between two tracks.

Drag marks aren’t always as obvious as the ones shown above. In the next photo you see the trail of a coyote walking from top to bottom. In the lowest part of the photo there’s a thin line that was made by a single claw. There are wider gouges above that made by the rounded tips of the feet. But again the grooves lie within the trail width and always connect to tracks.

In the next photo we see what at first glance looks like the trail of some kind of otherworldly creature. It’s actually several coyote trails moving from left to right on a frozen waterway. To sort this out we need to focus in on the trail of each individual animal. The central part of the sequence draws our eye first: There’s an wavy drag mark that seems connected with the series of tracks in the center. If we look at just those tracks we see that they were made by a walking coyote. The drag mark seems to touch the prints, but toward the right it swings to the side and misses the tracks. This tells us that it’s not a foot drag but something that’s being carried. Above the central area there’s a similar string of tracks, and if we concentrate on those we see that they were made by another walking coyote. A third track sequence which lies below was made by yet another walking coyote. The outer trails are close to, but not on top of, the central trail, so there must have been two animals following close behind the one with the food item.

This scenario is supported by the next photo, which was taken in a place where the coyotes slowed down to go through a culvert. The tracks are closer together and the drag mark is more irregular. The drag mark touches one coyote print but misses the others, so it wasn’t made by the coyote’s feet. It’s definitely evidence of something being carried.

As to what was being carried, we can say it was a medium-sized object with a blunt projecting part and enough weight to make a deep groove in the snow. Claws would be thinner, an animal’s nose would be wider, an ear would be softer, and a tail would be fluffier and lighter. That would seem to eliminate all the medium-sized, winter-active animals in our region. But there’s another possibility: the detached body part of a deer with a protruding bone. The area where I found these tracks is a popular spot for hunters, and in mid-December, when I took the photos, coyotes would still have been scavenging on deer carcasses.

I’ll never know for sure, but a deer part is a reasonable conjecture, and conjecture is often what we’re left with when we attempt to understand the trail of a predators carrying dinner. Even without definite conclusions, the process of sorting out the details can be satisfying in itself.

Zig-Zags

In past posts I’ve used the term zig-zag to describe certain track patterns. In this article I’d like to delve more deeply into how zig-zags arise and what they can tell us about the animals that make them. When we humans walk in a relaxed, natural manner we place our feet in a zig-zag pattern because each foot falls to its own side of the line made by our moving center of gravity, the center line of the trail. It’s easy to verify this: Just walk naturally in snow or mud or on a dry surface with wet feet and then look at your tracks. The same logic applies to birds, so we often see patterns like the one in the next photo, made by a turkey walking from left to right. Each print angles inward, which helps to distinguish right from left. The sequence, starting at the left, is right, left, right, left, right.

Two legged zig-zags are pretty straightforward, but four-footed animals also create zig-zags, and it’s not as easy to understand how a four-footed animal can do that. Watching animals helps, but it’s hard to follow foot placement when animals are moving in real time. Fortunately for us twenty-first century trackers, there’s a tool that can bridge the gap–the internet. So let’s take a look at a video of a horse. If you click on this link: Bing Videos, then click on horses walking youtube and start the video, you’ll see a horse walking in slow motion. Notice that as each front foot leaves the ground the rear foot on the same side comes down in the spot just vacated by the front foot. The video doesn’t show the pattern on the ground, but it’s easy to see how the horse leaves a series of double impressions, each one a front track overlaid by a rear track. And since the feet on each side fall to their own side of the center line, the overall pattern is a zig-zag. The trail in the next photo, made by a deer walking from bottom to top, is a good example of a zig-zag made by a four-footed animal.

But all zig-zags aren’t the same. The physical characteristics of animals vary, and this affects the kinds of patterns they leave when they walk. There are also different types of walks, with differing relative placement of the front and rear tracks. In the photo above the walk is an almost perfect direct register gait, meaning that the rear feet fell almost exactly on top of the corresponding front tracks. The next photo shows tracks made by a woodchuck walking from lower left to upper right (and just below the second impression, tracks of a squirrel bounding toward the bottom). The trail is more variable but the tracks are mostly in indirect register, meaning that the rear tracks fell partly but not completely on top of the corresponding front tracks. Starting at the lower left the track sequence for the woodchuck is: right rear on right front, left rear on left front, right rear, right front, left rear on left front. Even in this more irregular trail the zig-zag is apparent.

The width of the zig-zag, known among trackers as trail width, varies from one species of animal to another. To measure trail width, find a relatively straight part of the trail and imagine or draw out two parallel straight lines that just touch the outsides of the alternate sets of tracks. Then measure the perpendicular distance between the lines. This is diagrammed in the next photo of the indirect register track pattern made by a walking opossum heading toward the upper right.

In the next photo you see a trail made by a gray fox walking from right to left. The trail has a different look from the opossum and woodchuck trails, both because of its narrower width and also because the fox’s step lengths are longer. But the zig-zag is still apparent. Trail widths, combined with step length, can be helpful in identification, since chunky animals like woodchucks and possums make wider trails and take shorter steps than slimmer, longer-legged animals do. And trail widths are especially important when you’re considering animals with similar step lengths. For example, trail widths for a walking coyote are generally between 4 and 5 inches while trail widths for deer moving at a walk range from 5 to 10 inches. Even when the tracks are degraded or obscured by collapsing snow it’s usually possible to differentiate between a coyote trail and a deer trail.

Animals find it harder to move in deep snow, but when they’re walking their trails still show the zig-zag pattern. In the photo below a red fox walked from bottom to top leaving a zig-zag arrangement of deep holes in the snow.

All of the gaits discussed above (and the one the horse was doing in the video) fit into what I call the regular walk–also called the diagonal walk in the tracking literature. But that’s not the only kind of walk animals can do. A common variant is the overstep walk. To see a dog doing the overstep walk click on this link: Bing Videos and then click on dog gaits youtube and start the video. The recording shows a dog walking at actual speed followed by the same sequence in slow motion. If you keep your eye on the spot just vacated by a front foot you’ll see the corresponding rear foot come down a little past it. (This video also does a nice job with the amble, equivalent to the pace-walk of the raccoon, and the trot.)

The interesting thing about the overstep walk is that the pattern of tracks on the ground also makes a zig-zag, but the points of the zig-zag consist of sets of two prints, front and rear from the same side, rather than the impressions of two superimposed tracks. In the next photo you see an overstep pattern made by a house cat moving from lower right to upper left. Because a cat’s front tracks are wider and shorter than the rear ones we can see that in each set the front track is behind the rear. The sequence, starting at the lower right, is: right front, right rear, left front, left rear, right front, right rear. Among animals that are habitual walkers, overstep walks are common.

Another variation you’ll come across is the understep walk. The next photo shows the trail of an opossum doing an understep walk, heading from the lower left to the upper right. Again, the prints are arranged in sets of two, each set the front and rear from the same side. In each pair the hand-like hind track, with its thumb pointing inward, lies behind the front track with its more evenly spread toes.

We sometimes find zig-zag walking patterns in the trails of animals that aren’t habitual walkers. Fishers move mostly in bounds or lopes, but they walk when extra caution is needed or when the footing isn’t secure. The trail in the photo below was made by a fisher walking, mostly in direct register, from lower right to upper left.

Walking trails are less common for minks than for fishers, and for minks it seems to be mostly about the animal’s dislike of unstable surfaces. In the next photo a mink walked from right to left through mud (looking pretty dry in the photo but probably much wetter and slipperier when the tracks were made), leaving sets of paired tracks. But which walk is this, overstep or understep? We can tell because the middle toe in the mink’s hind print usually angles a little to the outside. So the sequence, starting at the right, is: left rear, left front, right rear, right front, left rear, left front, right rear, right front, and this is an understep walk.

White-footed mice are even less likely to walk than minks, but the next image attests to the fact that they do it on rare occasions. A white-footed mouse walked from bottom to top, leaving sets of paired tracks. The four-toed front prints lie behind the five-toed rear prints in each set, so the mouse was doing an overstep walk. The trail both before and after the walking part was on drier footing with normal mouse bounding patterns, so it was the wet mud that made the mouse shift to a walk.

Many animals get around mostly at a walk, and zig-zags abound in the tracking world. The details of the patterns can tell us a lot about the nature of the track maker. But the sight of a zig-zag for an animal whose default gait is not the walk is an even more compelling call to investigate. In addition to their help in species identification, zig-zags can tell us how animals interact with each other and with their surroundings. In this post we’ve only made a start. There are other kinds of zig-zags, and even patterns that look like zig-zags but aren’t. I’ll keep these topics for a future article. In the meantime, follow the zig-zags wherever they lead.

Perfect Perches

Perches–they’re important to wild creatures for many different reasons. The gray squirrel in the opening image (from yardandgarage.com) is using a perch as a feeding site. The next photo shows a Norway spruce whose dead lower branches provided feeding perches for a red squirrel. You can see how the piles of inedible cone cores and scales accumulated under the branches the squirrel perched on. These accumulations are called middens, and they can build up over time into substantial mounds.

Favorite perches often show signs of usage. The red squirrel that used the perch shown below left a cone scale and a number of opened seeds, some with wings still attached.

Red squirrels may mark perches by biting them. In the next photo you see a Norway spruce branch that bears the distinctive paired incisor marks made by a red squirrel. The lower branches of conifers are usually dead, so these marks don’t heal over and may last quite a while.

In the next photo you see a discovery I made during summer a few years ago. The Norway spruce cone crop that year was early and abundant, and a red squirrel had left a cone core, stripped of its supply of edible seeds, resting on the perch it had used. And in case you’re wondering, no, I didn’t put it there, it was all the squirrel’s doing. The scales that dropped as the squirrel fed can be seen on the ground at the base of the tree.

The photo below shows an unusually well elevated feeding perch used by a gray squirrel.

In the next photo you see what I found on top of the log: the remains of an acorn the squirrel had fed on.

Here’s a perch used not for feeding but for food storage. A gray squirrel lodged a black walnut in the crotch of a honeysuckle branch. I’m not sure what the squirrel’s motivation was–perhaps it was to keep the walnut away from other squirrels.

A perch doesn’t need to be overly high to be suitable. In the next photo you see a log used by a squirrel–it could have been a red or a gray–feeding on a white pine cone.

Rocks can also make good perches. Last August a red squirrel harvested young larch cones and brought them to the rock shown below for consumption. Where rocks or logs are available they are preferred over ground level feeding sites.

But food isn’t the only thing drawing animals to perches. A red fox balanced on the log in the next photo in order to deposit its scat. Scat is important in intraspecies communication, and wild canines prefer to leave their scat in conspicuous positions. Sometimes this requires a little acrobatic ability to position the scat just right.

One of my favorite spring experiences is hearing the drumming of ruffed grouse. Males in search of mates perch on logs or other raised features and beat their wings to produce a resonant booming sound. They prefer platforms that are unobstructed and raised well off the ground. You can see a spot in the center of the image where the bark was dislodged by the drumming bird.

Perches can also be used as observation posts. In the next photo you see a mound of earth thrown up by a falling tree. There were tracks–they were barely visible so I didn’t include a photo–going up the side. The size of the impressions suggested a fox.

On top of the mound (shown in the next photo) there were obvious signs of disturbance, showing that it had been used as a perch. The fox would have sat quietly while it listened, looked, and sniffed for signs of prey animals.

We seem to have circled back around to the topic of food, so here’s my last example of a feeding perch. A black bear climbed the beech tree in the photo below and pulled a nut-bearing branch inwards until it broke off. The bear consumed the goodies, pushed the branch aside and pulled another one inward until it broke. The discarded branches formed a tangled cluster, and the bear might even have stood on the growing mass of harvested branches as it continued to pull more branches in. These branch clusters are known by the somewhat misleading term bear nests, although they have more in common with squirrel middens than with nests. With healthy beeches becoming less abundant, bear nests in beech trees are harder to find than they used to be, but the same kind of sign occurs in apple, black cherry, serviceberry, and oak trees.

Wild creatures know their territories in minute detail, and they’re familiar with all the best perches. The attributes of a perfect perch vary somewhat with the specific animal and situation, but safety and accessibility are always important. The location also needs to be appropriate to the animal’s purpose, whether it’s to consume food, to find food, or to advertise its presence. If we stay alert for perches we can begin to understand what makes a good perch and what they can tell us about the lives of the animals.

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.

Photo from Deeryproof

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.