Tag: overstep walk

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.

Bears on the Move

[A note about last month’s post: you may have gotten a belated notification of the June blog; if so, my apologies. I had some trouble with my website, and the messages didn’t go out until the problem was fixed.]

Imagine you’re hiking on a sandy forest road, checking all the good spots for tracks. Suddenly you’re surprised to see what appear to be the barefoot tracks of a person. Could someone have been walking around way out here without shoes on? But as you look again, you realize that there’s something odd about the prints. Instead of the big toe being on the inside of the foot, it’s the outside toes which are larger and positioned farther forward. In fact, the big toe isn’t really very big. And ahead of each toe there’s the unmistakable mark of a claw. These tracks belong to a different creature altogether–a bear.

The black bear (the only bear we have in the east) that made the tracks above was moving at an indirect register walk, placing each rear foot on the spot just vacated by the front foot from the same side. The zig-zag pattern matches the pattern made by a walking person, but it’s a messy zig-zag because the coverage of the front prints by the hind ones isn’t precise. That’s a sure clue that the trail was made by a four-footed creature.

Another kind of movement often used by bears is the overstep walk, a gait in which the rear foot comes down just ahead of the front foot on the same side. In the next photo a bear moved from bottom to top at an overstep walk, leaving a sequence of tracks made up of sets of two. Each set is composed of a hind track trailed by a front track, and the pairs of tracks are arranged in the familiar zig-zag of a walking gait. Starting from the bottom, the sequence of tracks is: left front, left rear, right front, right rear, left front, left rear.

In the next image you see a left front and a left rear print taken from an overstep walk sequence. The direction of travel is toward the right, and the rear print with its fully impressed heel looks larger–and more human–than the heel-less front track behind it. In both front and rear tracks the outer toe (the upper one) is slightly larger than the others, but compared to human tracks the difference in size is less pronounced. The inner toes shows nicely in both tracks, and they’re distinctly smaller than the rest. There are a few claw marks, but they’re not easy to find because they’re not exactly in front of the corresponding toes.

Bears are classified as plantigrade creatures, meaning that their heels often touch the ground when they are moving at a normal walk. I’m hedging a bit here because heel registration in bears is variable. Rear tracks may show complete and well connected heels, as in the photo above, or partial heel impressions as in the upper sets of tracks in the preceding photo. And if you look at the first photo you’ll see heel marks that are separated from the middle pads by ridges.

Front prints commonly lack heel impressions, but there are times when the full length of the front foot, from heel to toes, does register in the track. The right front track in the next photo (direction of travel toward the left) is a good illustration. The middle pad forms a broad, slightly curved depression in the center of the photo. To the left the four largest toes and their claws show as clear imprints, but the smaller fifth toe (which would have been toward the bottom of the photo) didn’t touch firmly enough to register. To the right of the middle pad there’s a separated circular impression made by the heel pad.

Female bears which bore young over the winter are now travelling with their offspring and leaving tracks like the ones in the next photo. At the lower left you can see the mother’s print. The more delicate prints of the cub, with their prominent claws, are above and to the right. Young bears are active and playful, but they are also vulnerable to predation by coyotes, bobcats, and even adult male bears. Those sharp claws allow cubs to climb to safe refuges high in trees.

Bears are constantly on the move to access a variety of seasonally abundant food sources, often travelling miles as wild fruits and nuts ripen, colonial insects become available, or crop plants mature. Wherever they cross silt beds, sandbars, muddy forest roads, or other trackable surfaces they may leave prints for us to find. So when you find tracks that bear an uncanny resemblance to human tracks, look again. You may be on the trail of a roaming bruin.

What’s Underfoot Makes All the Difference

I’ve been finding lots of coyote tracks lately, and as I go back over my photos I’m amazed at how different they can look from one another. It’s not that the substrates are radically different–just sand, silt, or mud. And to make my point I’ve narrowed down the gaits to just walks and trots. But still, no two tracks are alike. How can what seem like small differences in conditions give tracks such strikingly different appearances?

Moist, dense sand captured the tracks of a trotting coyote shown below, a front at the lower left and a rear at the upper right. The animal’s feet sank in just enough to show lots of details: the difference in size between the front and rear prints, the compact positioning of the toes, the greater depth toward the tips, and the alignment of the claws straight ahead. Both middle pads show only lightly, and the smaller pad of the rear print can barely be seen. In the front track there are small clumps of sand in the two leading toe impressions that were tossed there by the claws when the foot was lifted.

But all sand is not the same. In the photo below of a front print (for the sake of comparison I’ll stick with front prints for the remainder of this article), partial drying resulted in dark toe and middle pad impressions surrounded by lighter dry sand. I suspect that the sand was uniformly wet when the track was made. If the sand around the perimeter of the track had been dry when the coyote’s foot impacted, it would have lost its coherence and crumbled or flowed outwards. Instead pressure from the toes formed plates and fissures (known to trackers as pressure releases). Since nothing disturbed the track before I found it later that morning, these formations dried without disintegrating (although part of the ridge between the two leading toes did fall to the side).

In addition to the larger areas of dry sand there are tiny, light colored squiggles in the floors of the toe and middle pad impressions. These also indicate that the sand was wetter when the track was made; small bits of wet sand adhered to the coyote’s toes and middle pads (dry sand doesn’t do this), and came up as the foot was lifted. Being slightly elevated and also less dense, these particles dried faster than the packed floor of the track. You can see the same thing at an earlier stage of drying in the first image.

This kind of partial drying can often tell us how long ago a track was made. Dew creates wet soil surfaces, so tracks made early in the morning in substrates subjected to dew-fall look uniformly moist immediately after they are made. But on dry summer days the elevated parts begin to lose moisture quickly, and lighter colored halos form around the darker depressed parts of a track. As the substrate continues to dry the entire surface becomes lighter in color and the structure in the cracks and plates disintegrates, resulting in a track with softer edges and uniformly lighter color. Another round of dew-fall and daytime drying may reproduce the halo effect, but the softer edges usually give away the greater age.

The track shown below was made in dry sand, and any structure that existed within the sand disappeared with the impact of the coyote’s foot. Instead of forming plates and cracks in response to the pressure of the foot, the sand moved more like a liquid, producing soft outlines and rounded pressure releases. Although some detail was lost, the compact form of the foot and the triangular shape of the middle pad are still evident. If this track was moistened by dew-fall the night after it was made, it would look wet early the next morning and would develop a lighter colored halo as drying progressed. But the rounded edges would show that it was made at least a day earlier, when the sand was dry.

The photo below shows what fine, moist mud can do to reveal track features. The toes and middle pad are crisply outlined and show very little disturbance, suggesting that it was made at a walk. In front of and behind the middle pad (and a bit at the sides of the toes) there are impressions of the hair which fills the spaces between and around the toes and middle pad–in November, when I found the print, the coat was already thickening ahead of the cold weather to come. We even see the slightly pebbled texture of the skin, especially in the middle pad. This beautifully detailed print illustrates several important diagnostic features of coyote tracks: the trim outline with tightly held, forward pointing toes; the lack of claw imprints telling of shaping through natural abrasion; and the outline of the middle pad with its triangular forward edge and lobed trailing edge.

You may wonder why particles of mud weren’t lifted from the floor of the track the way clumps of sand were in the first two examples. After all, mud is sticky, isn’t it? It certainly is, and the stickiness shows in the narrow ridges pulled in by the toes and the middle pad. This is especially obvious in the lower edge of the left leading toe, the back edge of the right outside toe, and the back edge of the middle pad. But mud is also very fine-grained and has greater internal coherence than sand, so it doesn’t pull apart as easily, especially after it is compressed by the weight of an animal’s foot.

In the next photo the silty mud was not as wet and was much firmer, so the track is shallower and the toes and middle pad look smaller. It’s not that this coyote actually had smaller toes. It’s rather that less of the toe and pad surfaces touched the mud. Think of holding a beach ball and pressing it into soft beach sand to make a large circular impression, then compare that with pressing the ball onto a sidewalk where the contact area is much smaller. The outer toes look especially small, and the lobed trailing part of the middle pad is narrower compared with the same area in the previous photo. Another striking feature is the disturbances in the toe impressions. Cracks and displaced sections in the forward parts of the toes show that the foot pressed backwards against the substrate. These and the tiny punctures made by the leading claws suggest that the animal was moving with more energy (perhaps at an overstep walk or trot) than the coyote that made the track in the previous photo.

Finally, here’s a slightly quirky example of the way tracks can come to have different appearances. I found the print shown below on a truck trail that had been surfaced with pulverized rock quarry tailings. The coyote had walked through a stretch covered with fine white rock dust before it crossed the dried mud in the photo. The dust adhered to its feet and was deposited on the mud to make light tracks on the darker background. As in the previous photo, the toes and middle pad are relatively small and separated by wide negative spaces, but the diagnostic features of a coyote print can still be seen.

There’s so much to learn from tracks: how the track was made, what the conditions were like at the time, how old the track is, and what happened after the animal passed by. We can even get glimpses of some of the challenges in the daily lives of animals. Understanding the subtle (or not so subtle) differences in the appearance of tracks can help us to delve deeper into the myriad messages tracks carry.

A Closer Look at Deer Tracks

A deer track–so familiar that we may pass it by without paying much attention. But a closer look at a deer track can reveal some unexpected insights. In the photo above the two main toes (called clouts or claws) show as paired depressions separated by a ridge. In each clout the broader rear edges are rounded and the narrower forward ends are bluntly pointed, so the direction of travel is to the right. When the toes are placed close together the way they are in this photo, the overall shape is vaguely heart-shaped.

Here’s another shot of deer tracks, in this case a left front (at the lower left) and a left hind (at the upper right). Front prints tend to be slightly wider and more rounded than rear prints, but the differences between front and rear are not nearly as pronounced as they are in most other mammals.

Now look at the first photo again: it’s actually a rear print superimposed almost exactly on top of a front (which trackers call a direct register). The clue to the double impact lies in the right toe impression: along the leading part of the outer margin there’s a slight crack and a sloping edge. The outer edge of the left clout is more like a vertical cliff. The left outer edge of the rear foot came down even with the left edge of the front, but the right outer edge landed a little inside.

It helps to have a track pattern when wrestling with such matters. The deer in the photo below was doing an ordinary walk (also called the diagonal walk, for reasons connected with the footfall sequence), and it left the zig-zag track pattern typical of the gait. Each “print” is actually made by two feet, first the front and then the rear on the same side.

The next photo shows the double impact more clearly. In each impression you can see part of a front track with a rear on top and slightly behind (know in tracking circles as an indirect register). I call this the ordinary walk because it’s one of the most common gaits of both wild and domestic animals (and because the term is less abstruse than ‘diagonal walk’), but it’s only one of many variations on the walk. The patterns associated with the various kinds of walks vary, but if you can recognize the zig-zag arrangement of the ordinary walk you’re well on your way to understanding these and other gaits.

But how does that pattern come about? Gaits can be hard to understand, especially if you haven’t spent much time watching animals move. Fortunately there are lots of helpful videos available to make up for this lack. Here’s one that shows the ordinary walk really well: https://www.bing.com/videos/search?q=animal+tracking+gaits&view=detail&mid=11CC299AF70EC963C01211CC299AF70EC963C012&FORM=VIRE.

You should go past the galloping dog and the trotting horse and focus on the third sequence, a horse walking in slow motion. You’ll see each hind foot landing in the place just vacated by the front foot on the same side. If you’re curious about the variations I mentioned there are a few later in the video. For example the first cat sequence is an overstep walk, in which the hind foot passes the front foot track and lands just ahead of it.

When a deer is moving faster or more erratically its tracks can look very different. In the next photo of a left rear print, the ridge separating the clouts widens out toward the front. Note also that the two toe impressions don’t look the same: the left one is relatively level but in the right one the tip area and right edge are deeper. This suggests an energetic turn to the right, and this deer was, in fact, making a playful jump to the right.

The deer tracks in the photo below are even less like our idealized image of deer tracks. This animal was galloping from left to right in soft, moist sand, and its feet sank in so much that both the main toes and the dewclaws made deep impressions. These are both left feet, the front on the left and the rear on the right and the differences in the front and rear dewclaws show nicely. In the front track the dewclaws are closer to the main toes and are angled sideways, while the hind dewclaws are slightly farther behind and point more forward. The energetic movement caused the tips of the toes to sink more deeply than the back parts of the clouts. When the feet came up out of the sand the toe tips dragged and parts of the track walls were broken and scattered, adding to the atypical appearance of the tracks.

If we recognize the kinds of differences I’ve illustrated we can go far beyond basic track identification. Track variations can tell us about the movement and energy of the animal, what it was paying attention to, and maybe even why it was moving the way it was.