Tag: trot

Possum Puzzles

The opossum is a humble animal, slow moving, shy, and generally of a placid disposition. But opossums can present surprising challenges to the tracker, not the least of which is getting a handle on the tracks themselves. To understand opossum tracks it may be helpful to see the animal’s actual feet, so let’s take a look. The photo below shows the underside of the left rear foot of an opossum–it resembles a human hand with a large, widely angled thumb and four additional, finger-like toes. If you hold up your left hand with the palm facing you, you’ll see the resemblance. Try to imagine your hands as the rear feet of the animal.

Cornell Wildlife Health Lab

In the next photo you see the opossum’s left front foot–very different from the rear. The five toes of the front foot are somewhat finger-like and similar to each other in shape, and the middle pads are quite bulbous. Both front and rear feet are adapted for climbing but are less ideal–especially the rear feet–for moving on the ground. This, combined with the animal’s heavy body and relatively short legs, means opossums are not very agile.

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Now let’s look at opossum tracks. In the photo below the right front track lies on the left and the right rear track lies behind it on the right, both tracks oriented toward the left. The spreading toe indentations of the front track radiate from a compact grouping of middle pad impressions. In the rear track the thumb points to the side (downward in the photo), and the other four toes are closer together and angled to the opposite side (upward in the photo).

Because the opossum rarely moves faster than a walk (or sometimes a trot), front and rear prints are often partly superimposed, and that’s another source of confusion. (The animal whose tracks are pictured above was drinking at a puddle, so it left some nicely separated prints.) In the photo below you see a left rear and a left front track, oriented toward the right. The two tracks are so close together it’s hard to tell where one ends and the other begins. If you look at the right side of the frame you’ll see five similar toe marks radiating outward from four closely set middle pad impressions. That’s the left front track. The hollow made by the thumb of the left rear track sits just behind the front middle pads, and above it you can see the middle pad and toe indentations of the left rear track.

The indirect register walk is the opossum’s preferred gait, so we often see sequences of front and hind prints like the ones shown above. In the photo below an opossum walked from the lower left to the upper right, leaving the zig-zag pattern typical of the walk. Each angle of the zig-zag is composed of front and rear prints from one side, and in each of these couplets the hind print lies just behind the front print. The sequence of tracks is right rear, right front, left rear, left front, right rear, right front, left rear, left front.

When tracks are less distinct, possum trails can be downright perplexing. The next photo shows another walking opossum trail, again proceeding from lower left to upper right. The rear feet fell farther behind the front feet at each step, but the zig-zag pattern can still be seen. A few of the prints are recognizable as possum tracks, and the rest are just weird looking.

If an opossum needs to move a little faster it shifts into a trot, leaving a trail like the one shown in the next photo (oriented from lower left to upper right). It’s harder to sort out front and rear tracks in this trail because the snow was dry and the faster gait created more disturbance. But if you look closely you’ll see that the rear tracks are consistently just behind the front tracks. The sequence of prints is right rear, right front, left rear, left front, right rear, right front, left rear, left front.

We know it’s a trot because the trail is straighter than the walking trails shown in the previous photos, and the distances between the sets of tracks are slightly greater. There must have been a slight hitch in the gait of the animal that made this trail, because the claws of one of the right feet (it’s hard to tell whether it was the front or the hind) seemed to brush the snow each time it moved forward to the next landing spot.

You may have noticed that none of the possum trails I’ve shown so far have tail drag marks. Opossums don’t drag their tails as often as people may think, but it does sometimes occur. Here’s a photo of a possum trail (oriented from upper left to lower right) with a nice tail drag mark. Don’t worry if the direction of travel isn’t obvious–it’s hard to tell from the photo because of the angle. A fox left a galloping trail on the left side of the frame, moving from bottom to top.

Much of the opossum’s winter diet comes from scavenging on carcasses, and the animals don’t generally move very far away while a food source lasts. So if you come across a possum trail it’s worth following–you may find a feeding site, or even a den like the one shown in the next photo. I had to climb through and around lots of tangles and thickets, but I eventually found the den the opossum was using while it fed on a deer carcass not far away.

Opossum tracks and signs give us a window into the lives of the animals. But I’m fond of them for an additional reason: the tracks are just so quirky. In fact, the consistent peculiarity of possum tracks is one of the clues to their identity. So be alert for weirdness, and when you find it, consider the opossum.

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.