white-footed mouse – Linda J. Spielman

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.

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.

Mouse Maneuvers

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

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

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

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

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

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

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

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

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

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

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

Mud, Glorious Mud!

Unlike many people I know, I’m always sad to see the snow disappear for good. But as soon as I think of what comes next–mud season–I get excited all over again. The transition between the seasons is highlighted in the photo below. A gray fox had stepped in some mud and then left it’s muddy footprints on the snow as it walked from left to right. Each deposit of mud is made by first the front and then the rear feet from the same side, and the zig-zag pattern of the walk shows nicely.

Once the snow is gone, ordinary mud takes its place as a medium for recording tracks. In the next photo an opossum stepped in some mud at the edge of a puddle, leaving a collection of both complete and partially obscured prints oriented toward the left. At the upper left there’s a right front track with a right rear track just behind it. Farther to the right you can see part of another right front track. In the lower right corner there’s a nearly complete left front print and just the suggestion of a left rear behind it. The front prints show the five widely spread toes that are characteristic of the opossum. In the front print at the upper left the segments of the semicircular middle pad are especially clear. The rear track in the upper center shows the strikingly different form of the opossum’s rear foot: a thumb-like inner toe pointing inward and four additional toes close together and pointing outward.

One of the nice things about mud is that it can record the presence of animals that we don’t encounter during the cold season. A spotted salamander (or maybe two of them) walked through the mud in the next photo. These amphibians hibernate in winter and come out in early spring, so mud season is a good time to look for their tacks. There are two trips: one going from the left side toward the upper right and the other proceeding from left to right along the lower part of the frame. Each trail consists of a central drag mark made by the tail and a sequence of front and rear prints on each side. The patterns of the prints tell us that the animal(s) were moving at an understep walk, with each rear foot touching down just behind the front foot from the same side. In the lower trail you can see the difference between the smaller, four-toed front prints and the larger, five-toed hind ones.

The tracks in the preceding photos are pretty obvious, but it’s not always easy to spot tracks in mud. In the photo below there’s a patch of shiny mud in the center of the shot, and on the right side of that patch there are some tire tread marks. If you look on the left side of the same shiny mud toward the top you’ll see a red fox track. The animal was moving from top to bottom, and because there weren’t many muddy spots the print in the photo was the only one I could find.

The close-up below shows the same track, but in this view it’s oriented in the opposite direction, toward the top. The central mound typical of canine tracks can be seen, and the marks made by the hair on the underside of the foot show clearly. There’s even a partial impression of the bar in the middle pad.

Woodchucks, like salamanders, spend the winter below ground and often emerge just as mud season is beginning. The next photo shows the left rear track of a woodchuck at the upper left and a left front track at the lower right. The five clawed toes of the rear print show clearly–the middle three toes set close together and the inner and outer toes angled toward the sides. Behind the toes you can see the four segments that make up the middle pad. In the front track the four toes with their substantial claws can be seen. The subdivided middle pad of the front foot lies behind the toes, and the heel pads show as two depressions behind the middle pad. The front print has a curvature toward the inside, a trait typical of the woodchuck.

It takes a medium with a fine texture to show details of the tracks of very small animals, and what better medium than mud? In the photo below you see the tracks of a white-footed mouse bounding from lower left to upper right. The tracks are arranged in the typical rodent bounding pattern–two rear prints (in the upper right quadrant) that are widely set and almost even with each other. Behind the rear tracks, the front prints are set more narrowly and, in this case, slightly staggered rather than even with each other. Track details show beautifully, especially in the left rear (the topmost track) and the left front (farthest to the left). If we compare these tracks with the woodchuck tracks above we see the rodent family resemblance, especially in the rear prints. The symmetrical mouse front tracks are more typical of other small rodents than the curved front prints of the woodchuck.

You can’t ask for a better rendition of detail than the porcupine tracks in the next photo. Porcupines have unique foot anatomy: their tough, undivided soles have a pebble-like texture that gives the animals good grip when climbing. The photo shows a left front print and, just behind it and overlapping slightly, a left rear print. The tracks are heading toward the left, and the texture of the soles shows beautifully. Because the leading edge of the rear foot touches the trailing edge of the front track, the two tracks seem to be joined together. You may be able to pick out the claw marks of the hind print along the leading edge of the sole of the front print. The four claws of the front foot made indentations at the very left, and if you look closely there are marks made by the three outer phalanges of the front foot behind the claw marks.

Once the snow melts and the weather warms, mud may not last long. Puddles may dry up and wet areas may fill in with plant growth. But mud can also appear in new places, and abundant rainfall can bring on new mud seasons long after the early one is over. As a matter of fact, I found the porcupine tracks in the photo above in the month of July. So keep an eye on the conditions of the puddles in your neighborhood, and don’t be surprised if you come across some beautiful mud when you least expect it.

Sorting Out the Small Rodents

Rodents are considered one of the most successful groups of mammals, so it’s not surprising that the northeast hosts many different kinds. They range in size from the tiny woodland vole (weighing an ounce or less) to the beaver (50 pounds or more). The small ones dominate, both in abundance and in their potential to confuse. Most of these little creatures are active in winter, so it’s a perfect time to get a handle on their distinguishing features.

The photo below shows a set of prints made by a red squirrel bounding from left to right. The five-toed rear tracks are nearly even with each other and set widely, their three middle toes parallel and their inner and outer toes diverging. The four-toed front tracks are set more narrowly and staggered, and their four toes are slightly splayed. Behind the toe impressions, the middle pads of both front and rear feet (analogous to the bumps over the knuckle joints in your palm and the ball of your foot) appear as clear indentations. The heel pads of the front tracks (like the heel of your hand) show in both right and left front prints, and the heel area of the right rear track (analogous to the heel of your foot) is a smooth elongation behind the middle pads.

Here’s a chipmunk group of four, with the direction of travel this time toward the top. The left front and rear tracks are partly superimposed, but the similarity to the tracks in the first photo is plain to see. This is what I call the rodent foot plan, and once you absorb it you’ll recognize it in other small rodents, including squirrels, chipmunks, mice, and voles.

But there are some variations which–if available–can be important in pinpointing an identification. The photo below came from the bounding trail of a southern flying squirrel, an animal similar to a chipmunk in body size (although lighter in weight). Compare the middle pads in the right rear tracks (the farthest to the right in each photo): in the chipmunk they’re well separated and form a sharp curve. The middle pads of the flying squirrel are closer together and form a gentle crescent.

If your reaction to that is, ‘you’ve got to be kidding!’ you’re not far off base. It’s a real difference, but snow conditions are rarely perfect enough to see that kind of detail. So how often can we be sure which small rodent made the tracks we’re seeing? Quite often, it turns out, because we have two additional diagnostic tools: trail width and habitual movement patterns. The tracks in the photo below, a white-footed mouse bounding toward the upper right and a gray squirrel bounding toward the lower right, are similar arrangements but are vastly different in size. In this case it’s easy to know which is which, but for less obvious differences, such as red squirrel versus gray squirrel, measurement of the overall width of the pattern, known as the trail width, can really help.

To measure the trail width of a bounding animal, imagine or mark lines parallel to the direction of travel which touch the outermost parts of the two rear tracks. Below you’ll see the same photo with lines delimiting the trail widths. Next, measure the distance between the two lines. The nice thing about this is that the trail widths of our most common small rodents fall into a simple size progression. In inches, trail widths for white-footed and deer mice measure 1 1/4-1 3/4; chipmunks, 1/1/2-2 3/4; red squirrels, 3-4 1/2; and gray squirrels, 4-6. At 1 3/4-3 inches the trail width for southern flying squirrels is similar to that of chipmunks, and northern flying squirrels, at 2 3/4-4 1/4 inches, overlap on the low side with red squirrels. Although trail width can be determined for any gait, the bounding gait so common in small rodents is especially suited to this measurement.

Habitual movement patterns are another useful tool for identifying small rodents. In the next photo a gray squirrel bounded at a good clip from bottom to top, leaving groups of four prints separated by relatively long distances. In each group of four the landing tracks of the smaller front feet are behind the take-off tracks of the larger rear feet. Bounding trails of red squirrels and chipmunks are similar in overall proportions. It’s not that these animals always make long leaps. If they’re moving slowly the distances between the groups of four can be smaller, and the hind feet may not pass as far ahead of the front feet. Compare the arrangement of the gray squirrel prints in the previous photo with that of the slower moving red squirrel in the opening illustration. The point is that the habitual travelling movement of these animals creates trails with characteristic four-track groupings and relatively large spaces between groups.

Compare the pattern above to the next photo, the trail of a southern flying squirrel, bounding from lower right to upper left. In this trail the larger rear prints are behind the smaller front ones, and the distance between the groups of four is smaller. In the trails of northern flying squirrels the rear tracks are often ahead of the front, but both species of flying squirrels have sacrificed strength for lightness and aerodynamic design and are unable to match the long leaps of their non-gliding relatives.

Snow depth can affect the foot placement of bounding rodents. To the white-footed mouse that made the tracks in the photo below the snow was fairly deep, so the groups of four are reduced to sets of two, each of the paired impressions made by sequential impacts of front and rear feet from the same side. All of the rodents I’ve been discussing do this when deep snow makes it more energy efficient. But even in these reduced patterns trail width can still be measured, as long as we make sure we’re looking at the actual tracks and not the larger openings around them. And like squirrels and chipmunks, mice make shorter leaps when moving less energetically. An example of mouse trails with consistently shorter leaps can be seen in the opening photo of last month’s article.

Meadow voles are chunkier and have shorter legs than white-footed mice, so they can’t make long leaps, but their trails are roughly as wide as those of mice. It’s not always easy to tell whether a bounding trail with short leaps was made by a vole or a mouse, but if the trail goes on long enough differences usually show up. A vole’s foot placement is rarely as even and foursquare as that of a mouse, and voles tend to make frequent shifts in gaits. It’s not unusual for an individual vole trail to vary among lopes, bounds, trots, overstep walks, and scurrying gaits that are difficult to categorize. In the next photo there’s a partly roofed vole tunnel meandering between the lower right and the top center. A vole traveled from the left side of the frame toward the tunnel in a bounding gait, with typical short leaps and uneven foot placement. The thin line in the center of the trail was made by the tail.

If you’ve made it this far in this treatise, you may feel like your brain is reeling. Believe it or not, I had to leave out many details, and I haven’t even addressed the issue of distinguishing small rodents from other small mammals. The important thing is to get started. Every time you work through a small rodent puzzle you’ll learn more. So be patient and persistent, and enjoy the eureka! moments when a few puzzle pieces fit together to form part of the larger picture.

Animal Artists

Nature is the original artist. Whether it’s the pattern of ice crystals in a frozen stream or a flock of birds wheeling together in the sky, we’re surrounded by striking compositions. And animal tracks are no exception. I’ve been photographing these works of art over the years, and I’d like to share some of my finds with you. For each one I’ll also include my deductions and speculations on how it came to be.

Those are mouse trails (deer mouse or white-footed mouse) that seem to pour out of the upper right corner of the photo below. In each trail the deeper landing spots are connected by lighter tail marks. The indistinct trail farthest to the right is older than most of the others. To the left of that one is a trail (superimposed on another older one) that looks like it is heading uphill, based on the shorter jumps and the angles of the tracks. The next one to the left (mostly centered in the photo) seems to be a single passage, and a few tail marks that go to the side (check out the small mark above the lowermost landing spot) tell me that the mouse was going downhill. The trails farther to the left are combinations of at least two passages, and it’s hard to say which way the animals were going. All of the trails radiate from a depression in the snow next to a tree trunk at the upper right of the photo. Openings like this allow access to spaces under the snow pack which are crucial for the winter survival of small animals.

The tracks pictured below were made in a warmer season. A toad walked through the mud and left some natural calligraphy. The direction of travel is from right to left, and the front tracks, with their four toes oriented inward, lie inside the rear ones. The curved lines were made as the trailing toes of the front feet occasionally dragged through the mud as they touched down. Toads often seem to walk on the tips of their rear toes, which is why the hind tracks look like curved rows of dots. The difference between the front and hind prints is best seen in the tracks from the left side (the lower ones) where there’s more separation between the two. At the extreme left there are two left rear tracks near one left front. It looks like the toad put its rear foot down lightly, picked it up and put it down more firmly nearer to the front print.

If you’re having trouble picturing how the feet of a toad could be positioned to make tracks like these, this photo of an American toad might help.

Snakes can also produce artistic creations. A garter snake made the designs in the sand shown below. The sinuous trail near the stones was made by simple forward movement toward the upper left. You can see several places where the tail must have lifted and the back end moved slightly sideways, leaving a ridge outside of the main groove. It’s harder to figure out what happened in the lower half of the photo. The wider flattened areas suggest sideways movement, almost as if the snake was having a good stretch. Do snakes do that?

Meadow voles bulldozing their way through shallow snow made the next work of art. You can see tiny tracks in the grooves, too many to have been made by just one passage. Tail marks show in a few places. The haphazard nature of the voles’ travel suggests they were searching for something edible, seeds perhaps.

A crow is the featured artist in the next photo. The bird landed at the lower center and walked toward the deep hole just above center. It must have dug around there, maybe in search of some edible item. (Or did it already have something that it put down and manipulated there?) It then turned to the right and took off, leaving a tail mark to the left of the hole and a pair of nearly symmetrical wing marks to the right. (If it had been landing instead, the wing marks would be next to or to the left of the hole.) There are some additional feather marks in the photo that are harder to figure out. The ones in the lower right corner that seem to drag down to the left may have been made when the crow landed. Just above those there’s another set of wing marks, and there are two more on the left side of the frame, one above and another below the tail mark. These are more of a puzzle, since they don’t seem to be connected with the landing or the take-off. Maybe the crow swooped around before it actually landed, or maybe another crow was harassing it.

I’ve saved my favorite one, a red fox track decorated with ice crystals, for the very last. This is an interesting phenomenon that occurs during very cold weather. When the track was made it would have looked normal, with a thin floor of compressed snow bordered by low walls of snow. After the fox stepped there the temperature stayed cold so the soil beneath the track, although frozen, was warmer than the air above. The warmth at ground level caused ice in the ground and the snow in the floor of the track to undergo sublimation and recrystallization. Water molecules became detached and formed water vapor, which moved upward and formed new ice crystals in the colder air just above. Since this was a slow process the new crystals had time to get much larger than the crystals in the original snow.

This same process gradually transforms solid snow at the bottom of a deep snow pack into a warren of tunnels and chambers. Remember the mouse trails in the first photo? The trails connected to an opening which gave the mice access to spaces under the snow pack created in the same way as the crystals in the fox track, by sublimation and recrystallization. You can read more about this process, called constructive metamorphosis, here.

Natural art is all around us, and expressed within this beauty are the lives and relationships of living things and the physical world they live in. It’s certainly possible to appreciate the art of nature on its own, without any deeper analysis. And if that is your inclination I encourage you to simply be open and drink in natural beauty whenever you can. But for me, understanding how nature works adds much more to my experiences of natural art. For instance, when I look at a track filled with ice crystals I both marvel at the delicate design and imagine how that design was created by water molecules drifting up from below and attaching to crystals at higher levels. I revel in both the beauty and the finely tuned interactions that produce it.

A Perfect Storm of Jumping Mice

I guess I was just in the right place at the right time. I was in a part of the western Adirondacks where the soils are sandy–they’re called glacial outwash soils, and they’re a gift from our glacial past. After a day with several heavy downpours the weather cleared, and the next morning I went out to look for tracks. I headed to one of my favorite spots, a sandy truck trail that meanders through a mosaic of wet meadows, marshes, and shrubby uplands. The low spots in the road had filled with water during the rain, but the sandy soil had allowed the pooled water to drain away, leaving perfect tracking mud.

And there were tracks aplenty, mostly small rodents. But not just the usual small rodents–many tracks had the distinctive features of a very special animal. In the photo below (direction of travel toward the top) the five-toed hind tracks are in the upper section, nearly even with each other and set widely apart. Below them are the four-toed front tracks, one leading the other and set more narrowly.

These are the tracks of a small rodent called the meadow jumping mouse. (It’s cousin, the woodland jumping mouse, is restricted to boreal forests and would not have been found where I was tracking that day.) The meadow jumping mouse is pictured in the photo below by Martha Beck (from her blog, Martha’s Blog). This beautiful little creature has a very long tail, large ears and eyes, long back legs, and really interesting rear feet.

Here’s another example of the tracks I found that day. The direction of travel is toward the right, and the front prints (on the left side) are distorted by the impact of landing from a long jump. Nevertheless you can see that the rear tracks (on the right side) are much larger than the front,

especially in this example in which the entire lengths of the rear heels touched down. These long heels are unique to the jumping mouse, as are the long, slender toes. The three central toes are often slightly curved, and they spread more than the corresponding toes of most other small rodents. Another special feature lies in the elongated middle pad area of the rear prints. The inner and outer toes attach considerably behind the area where the three central toes come together.

In the photo below, another one from that amazing day, the elongated middle pad area shows nicely in the left rear print (farthest to the left). The right rear track is on the extreme right, the two front tracks lie between the two hind tracks, and the direction of travel is toward the top. Some interesting details of the front prints can be seen in the right front print (the lowest of the group): it’s canted toward the outside, with the innermost toe pointing up and a little to the left, the toe next to it pointing almost directly upward, the third toe pointing toward the right, and the outermost toe pointing downward. The middle pad area of this track is in the center, and the paired heel pads show at the lower left edge of the print.

Once you’re aware of the critical details, jumping mouse tracks look very different from the tracks of other small rodents. The meadow vole tracks in the photo below, also from that wonderful day on the sand road, are in the same relative positions as the jumping mouse tracks in the previous photo. But the front and rear prints of the meadow vole are similar in size and there is no elongation of toes, heel, or middle pad. The inner and outer toes of the hind tracks show as small ovals on either side of the middle pad area, and the front tracks are only slightly angled.

Although their feet are larger, jumping mice are actually much smaller than meadow voles, but they’re similar in size to another common small rodent, the white-footed mouse. But white-footed mouse tracks are also very different from jumping mouse tracks. The white-footed mouse tracks in the photo below (direction of travel toward the top with hind tracks above and front tracks below) are tiny compared to jumping mouse tracks, and the toes in both front and rear prints are small ovals with no connections to the middle pad. The three central toes of the rear print are close together and parallel with each other, and the middle pads are a distinct series of bumps.

My walk along the sand road that day was a real revelation. Although the drying mud puddles may have been more attractive to jumping mice than to other small rodents, I still have to believe that the abundance of jumping mouse tracks indicated high population numbers. Those scattered, moist habitats were just the kinds of places favored by meadow jumping mice, and the muddy low spots were perfectly situated to capture the animals’ movements. Since jumping mice spend the winter in extended hibernation we don’t have the luxury of seeing their tracks in snow. But a perfect storm of favorable influences created conditions rivaling the best snow tracking, revealing jumping mouse tracks like I’ve never seen them before.

9/26 – I just got a comment from Janet Pesaturo about the range of woodland jumping mice, which is broader than I realized. They’re found in mixed softwood/hardwood forests in temperate zones as well as in boreal forests. Thanks, Janet.