house cat – Linda J. Spielman

What Do Claw Marks Tell Us?

Claws, like hair and feathers, are made up of proteins called keratins and are characteristic of mammals, reptiles, and birds. In mammals claws evolved into a variety of forms, including fingernails and hooves, but it’s the hard, tapered appendages we consider true claws that are the focus of this post. The marks they make in tracks can tell us a lot about the lifestyles and behaviors of their owners.

The gray squirrel right and left front tracks in the photo below (direction of travel toward the left) show conspicuous claw marks. The tiny pricks made by the claws tell us they’re quite sharp, as we would expect in an acrobatic climber like a squirrel. Behind each claw mark is a toe impression, and behind the toes there is a tight group of middle pads. Two heel pads lie at the back end of the track. The combination of sharp claws and protruding toe, middle, and heel pads is what gives the gray squirrel its excellent climbing ability.

There’s another interesting feature in these prints: on the inner side of each set of heel pads there’s an impression of the vestigial fifth toe, something not often seen.

Porcupines, although not as graceful as squirrels, are also good climbers, and their feet are equipped with impressive claws. The photo below shows three sets of front and rear porcupine tracks, all heading toward the upper left. At the lower right you see a left rear track with a left front track above and to the left of it. Almost directly above those there’s a right rear print with a right front print above it. At the upper left there’s another pair of left front and rear prints. In each set the hind track is the larger of the two. The spaces between the claw marks and the oblong sole areas appear at first glance to be unoccupied– porcupine toes frequently don’t register in tracks. But if you look closely you can see faint toe impressions in the front tracks. You’ll notice that the claws of the front feet make marks a little farther forward compared to those of the rear tracks.

Fishers are also good climbers, so it’s not surprising that their tracks show the marks of sharp claws. The next photo shows the left front print of a fisher, oriented toward the left, with narrow claw gouges at the tips of the toes. But fishers don’t just use their claws for climbing–these animals are predators, and their sharp claws are essential for catching and subduing prey. The five toes, each tipped with a claw, make a lopsided crescent, and the middle pad and heel area make up the rest of the print.

Claws also come in handy for digging. Striped skunk tracks, like the left front print shown below, have prominent claw marks which extend well ahead of the toes. The claw impressions are more robust the ones in the first photo–not very good for climbing but hefty enough to make good digging tools.

The presence or absence of claw marks is sometimes considered diagnostic for track identification, but, like many aspects of tracking it’s not an absolute. The next photo shows front (lower left) and rear (upper right) prints of a gray fox, direction of travel from right to left. Gray foxes have semi-retractable claws, and prints without any claw marks, like the ones below, are common. The same goes for bobcats and house cats, which have retractable claws.

But if a gray fox needs extra grip it can extend its claws, making tracks that look like the ones in the next photo. The larger front track is on the right and the smaller hind track is on the left, and the direction of travel is toward the top. By extending its claws the animal was able to gain more purchase in the soft mud. The marks vary in thickness because of the varying depth of the tracks and movement of the toes, but the rear track shows slender grooves which are consistent with claws that are very sharp. Although not as arboreal as squirrels and fishers, gray foxes are good climbers. Their sharp claws assist not only in climbing but also in capturing prey. Claw marks are sometimes seen in feline tracks under similar conditions.

Animals with retractable and semi-retractable claws are able to draw their claws completely or partially inside their toes. But all animals, even those with robust claws, can control their position by flexing or extending the toes. The front track in the next photo (made by a coyote walking toward the left) shows beautiful impressions of the toes and the middle pad, but no claw marks.

A coyote moving at a side trot toward the right made the front (upper left) and hind (lower right) tracks in the photo below. Claw marks lie ahead of all four toes of the front track, and ahead of the leading toes of the hind track. The depths of the tracks made at the walk and at the trot are similar, but the toes were flexed enough at the faster gait to make most of the claws dig into the sand.

Partial sets of claw marks often occur in wild canines. The coyote front (left) and hind (right) prints (direction of travel toward the left) in the next photo show tiny pricks ahead of the leading toes, indicating that just the tips of the two leading claws in each print touched down.

Dog tracks, like the front print (direction of travel toward the right) shown below, are more likely to have blunt, robust claw marks that routinely show in tracks, even when walking or at rest. In the photo the claw marks have rounded leading edges due to their wider tips. In addition to the blunt claw marks, the more rounded overall shape and the outward angles of the inner and outer toes are indicators of domestic dog rather than coyote or fox.

To further drive home this point, contrast the dog print above with the red fox front track (heading toward the right) in the next photo. The red fox claw marks are slender and pointed, and they’re oriented straight ahead–or even slightly inward on the leading toes. The claw marks of the inner and outer toes are tucked tightly against the sides of the leading toes. It would be rare for a dog track to show this kind of compactness in soft mud.

There’s a explanation for the differences between the claws of dogs and wild canines. Coyotes and foxes spend their lives on the move, so their claws are constantly shortened and shaped natural abrasion. Dogs spend more time resting and less time travelling over the landscape, so their claws are not naturally worn down and must be trimmed manually. Consequently, the claws of dogs are usually longer and blunter than the claws of coyotes and foxes. Similarly, the feet of wild canines have excellent muscle tone, and this creates tracks that are tight and compact. The less fit feet of dogs spread out more and leave tracks in which the toes and claws often angle outward.

Cottontail rabbits and snowshoe hares have thick fur on the bottoms of their feet, so claw marks don’t usually show in tracks. In the photo of snowshoe hare tracks below, right and left hind tracks (oriented to the right) take up the center, a smaller left front track heading toward the left lies on the left, and part of a left hind track, also heading toward the left, can be seen at the upper right. The fur thins out somewhat in the summer, but even in July when these tracks were photographed, it was thick enough to muffle the claw marks in the rear tracks. They do show just a little at the tips of the toes in the front track.

But rabbit and hare claws are surprisingly sharp. Rabbits defend themselves with strong kicks, and the claws can inflict real damage. Claws also help the animals to grip the ground in the weaving and dodging escape maneuvers that help them evade predators. In the next photo you see two rear prints made by a leaping cottontail rabbit. The claws dug in deeply to give the rabbit a powerful take-off.

Why claw marks appear the way they do, why they’re present or missing, how they’re used by different animals–these are all questions that deserve our attention. Every track we find presents opportunities to explore this topic further.

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.

Separating Felines and Canines

Cats and dogs–they live among us as companion animals, and their wild relatives are a familiar presence in our landscapes. The two groups differ from most other mammals in having four toes on both front and back feet, and in both groups there’s a smooth pad (the middle pad) behind the toes. So how to tell them apart? One thing we often hear is that canine tracks show claws and feline tracks don’t, but the presence or absence of claws can’t always be relied on. Cats can extend their claws if they need more grip, and the claws of wild canines may not touch the ground because they are naturally trimmed by constant movement. Fortunately there are other features that can help us to distinguish between canines and felines. It’s a simple matter of paying attention to details, and there are plenty of them. So let’s get started.

In the photo below you see the front track of a coyote, direction of travel from bottom to top. The overall shape is elongated, the toes are relatively large compared to the middle pad, and the outer toes are tucked tightly behind the leading toes. The middle pad has a pointed forward edge. Roughly in the center, between the toes and the middle pad, there’s a dome-like area, and an X is formed by the ridges between the middle pad, the outer toes, and the two leading toes taken together. The dome and the X are the negative spaces, areas that are not pressed down by toes or pads, and their arrangement is an unmistakable indicator for members of the dog family. (By the way, note that there are no claw marks.) And another important detail: the track is symmetrical. By symmetrical I mean that the right half is almost identical to the left half.

Here’s a way to grasp the concept of symmetry. In the next illustration I’ve added a vertical line which bisects the track. If you imagine folding the right half over along the line so it lies on top of the left half, the two halves will match almost exactly. The two leading toes are almost even with each other, the inner and outer toes are of similar size and spacing, and the middle pad seems to point straight ahead.

Now let’s compare a feline print. The photo below shows the front track of a bobcat. The overall shape is more rounded, the toes are relatively small compared to the middle pad, and they’re arranged in a wide arc in front of the middle pad. The left-most toe is smaller and farther back than the others. There’s no central dome, and the ridge between the middle pad and the toes is broadly curved or C shaped. Rather than pointing straight ahead, the middle pad is canted to the left. The arrangement of toes and middle pad makes the track very asymmetrical.

To get at the asymmetry here’s the same photo with a vertical line bisecting the track. If you do the mental experiment of folding one side over onto the other as we did with the coyote print, you’ll see that the two halves don’t match. One toe leads all the others, and the smallest one lags behind the other three. The whole print seems to be canted to one side. Because it’s asymmetrical we can tell which front print this is–it’s the left. If we were looking at an isolated coyote track it wouldn’t be possible to know if it was a left or a right.

Here’s the front print of another canine, a red fox. It’s not as elongated as the coyote print, but the overall shape is still more oval than round, and the outer toes are tucked in behind the leading toes. The central dome and canine X are unmistakable, and the track is beautifully symmetrical. In this case claw imprints show as delicate punctures directly ahead of the toes. The mud was just moist enough to show the hair on the underside of the foot and the chevron in the middle pad perfectly.

Perhaps you’re thinking that I oriented the bobcat track incorrectly, and that if it were rotated a little it could be made to look more symmetrical. But the asymmetry is inescapable, no matter how you look at it. In fact, when an animal is moving at a steady gait the correct orientation of each print is dictated by the direction of travel, and the imaginary bisecting line should be parallel to the direction of travel. The next photo shows part of a sequence of tracks made by a house cat moving at an overstep walk, a gait in which the rear print lies ahead of the front print from the same side. The direction of travel is from lower right to upper left.

In the next illustration I’ve added a line which defines the direction of travel to the same photo. (Sorry about the slight wobble, just imagine it’s really straight.) With the line as a reference, you can see that each track is canted to the outside. Also notable in this photo are the shapes of the middle pads: wide and blunt on the forward edges and scalloped on the trailing edges. The C-shaped ridges between the middle pads and the toes are especially striking.

The topic of gaits brings up another criterion sometimes said to distinguish canines from felines–direct register versus indirect register. Walking felines are said to place their feet in direct register, so that the back foot comes down exactly on top of the print of the front foot from the same side. Canines are supposed to prefer the indirect register walk, placing the back foot partly, but not exactly, on top of the front from the same side. But this isn’t a make-or-break test. The next three photos illustrate this point: first you see a bobcat direct register walk, next a bobcat indirect register walk, and finally a red fox direct register walk. The fact is that both felines and canines use both direct and indirect register walks. It’s fair to say that domestic dogs and cats are more likely to walk in indirect register than wild canines, but even among wild species there’s variation, and the difference isn’t very useful for identification purposes. And of course it wouldn’t apply in other kinds of walks, such as the overstep walk in the previous illustration.

Our other fox, the gray fox, makes tracks that are a little more catlike. In the photo below you see a rear print, below, and a front print, above. The overall shapes are round enough to be confusing, the central dome and canine X are a little different from the ones shown for the fox and the coyote, and in the hind track there appears to be a leading toe. Gray foxes have semi-retractable claws which don’t usually show in tracks, so the presence of claw marks suggests that the animal needed more stability in the wet mud.

In spite of the variations the tracks are clearly canine. Compare them to the bobcat tracks in the next photo, this time a left rear below and a right front above.

These two photos bring out some potential pitfalls in the task of differentiating canines from felines. Animal feet aren’t rigid, and toes may spread or tighten depending on the animal’s movement and the nature of the substrate. In the gray fox hind print the two leading toes gripped the soil differently, causing one to appear farther ahead than the other. The normal symmetry of canine tracks can be altered by head turns, changes of direction, or by sloping terrain. Another potential source of uncertainty is the fact the hind feet of felines are often more elongated than the front feet. In the bobcat photo above the rear track has a slightly canine appearance due to the tighter arrangement of toes and the more oblong shape.

And lastly, never underestimate the power of domestic dog tracks to create confusion. The track in the next photo was about the size and overall shape of a bobcat print, lacked claw marks, and mimicked the blunt middle pad and C-shaped ridge of a feline. Red flags were raised by the symmetrical structure and the large toes, but it was really the presence of more tracks which clinched the identity as dog. Domestic canines are incredibly variable–their tracks can be quite round and the tendency of the toes and middle pads to spread can give the negative spaces a feline appearance.

So the task of separating canines and felines is not always easy. Isolated prints are harder than more complete sequences, and weathering and distortions can make things difficult. But the more you study them, the better you’ll be at picking out the crucial features. And if one of these creatures is rare in your area, it’s a joy to find it’s tracks and know you’ve made a solid identification.