mink – 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.

Muskrats: Life in Two Worlds

Water and land: they pose very different challenges to the creatures that inhabit them. And yet some animals manage to live in both worlds. The muskrat is a semi-aquatic mammal, at home in the water and comfortable (although not as nimble) on land. The dome-shaped lodges made by muskrats (seen in the photo below) resemble beaver houses, but are smaller and are made with non-woody plants instead of the woody material used by beavers. When conditions are suitable muskrats make bank burrows with underwater entrances. Unlike beavers, they don’t build dams, and they prefer quiet or slowly moving water. Aquatic and semi-aquatic plants make up the largest part of a muskrat’s diet, but the animals also spend time on land harvesting non-woody terrestrial plants. They are also known to consume aquatic animals, including clams, mussels, crayfish, frogs, and fish.

A common sign of a resident muskrat is scat, usually found in small collections on rocks and logs that protrude above the water. These deposits announce a animal’s territorial claim to the pond, marsh, or stream where they’re found. The latrine shown in the next photo is on a large rock at the edge of a river, and it’s unusually large. The quantity and the combination of fresh and weathered scat indicate that a muskrat was actively patrolling its stretch of river.

On land muskrats generally move at a walk. In the next image the direction of travel is from left to right, and because of the snow the animal to placed its hind feet directly in the holes made by the front feet on the same side. A tail mark undulates between the tracks.

When the footing is more favorable muskrats use an overstep or indirect register walk. The trail in the next photo goes from upper right to lower left. Pairs of prints form an overall zig-zag pattern, and in each pair the rear track lies ahead of the front. The sequence, starting from the upper right, is right front, right rear, left front, left rear, right front, right rear. If you’ve noticed that the front prints seem smaller than the rear prints, you’re absolutely correct.

The difference in size is easy to see in the next photo. The right front track is on the left, and the right rear is on the right (direction of travel left to right). You can see all five toes in the front print–the tiny innermost toe is a little nub on the upper edge of the print just behind the full-size toe ahead of it. The four large toes of the front track are connected to the middle pad, and behind that there are two bumps that make up the heel pad. If these characteristics remind you of small rodent tracks you’re right on target. Muskrats are indeed rodents, although they have diverged from other rodents in many of their adaptations. In the rear track five toes can be seen, although the innermost toe impression is just the tip (above the other four rear toes and to the right of the third toe on the front print). The middle pad of the rear print made a partial impression at the bases of the toes, and–as is often the case–the heel pad did not touch down at all.

If danger threatens while a muskrat is on land, it hurries toward the safety of the water at a modified bound or lope. In the photo below you see a typical muskrat bounding pattern, with the smaller front tracks ahead of the larger and more widely set rear prints (direction of travel toward the top). The muskrat’s front feet slid forward into the soft mud, so the tips of the toes lie hidden in the muck. The larger rear feet didn’t sink as far and all five toes show clearly. Except for the relative positions of the front and rear tracks, this bounding arrangement is, again, reminiscent of the bounding patterns of many small rodents.

Muskrats possess a feature that is–as far as I know–unique among semi-aquatic animals: the toes of the hind feet are equipped with fringes of stiff hairs. In the next photo you see a left rear track, oriented toward the top. (There’s also part of a left front print to the lower right of the rear print.) The toes of the rear track are slender and finger-like, and the hair fringes make shelf-like impressions around them. These hair fringes add surface area and enhance the muskrat’s swimming ability. The smaller and un-fringed front feet are more suited to grasping and handling objects.

As you explore wetlands you’re likely to see swimming mammals, and you may find it difficult to know which creature you’re observing. There are clues that can help, starting with size. The smallest are water shrews and star-nosed moles. I’ve never seen shrews or moles swimming, so I’ll just point out that their size means they probably won’t be confused for anything but each other. Of the larger mammals, the ones whose tracks and sign we’re likely to find, the smallest is the mink. Minks swim with their entire body visible above the water, from head to furred tail. Their bodies are long and slim, their ears protrude from their heads, and their tails can usually be seen gently swaying from side to side on the surface. Muskrats are heavier than minks but their chunky bodies are about the same length. They swim with their heads and bodies showing above the water. The muskrat’s hairless tail is flattened vertically and can be seen undulating from side-to-side at the surface. The ears are small and don’t protrude from the head.

Next in the size progression (going by weight) is the river otter, with a body length of two to three feet and a powerful, furred tail that tapers from a muscular base to a small tip. Otters often swim with just their heads showing above water, but they may also undulate up and down or make short, playful swerves and dives. Their ears protrude noticeably from their heads. Our largest semi-aquatic mammal is the beaver, with a body length about the same as an otter but weighing up to twice as much. Beavers swim with most of the body and the tail below the water surface, and their ears protrude from their heads.

Muskrats are one of our most common semi-aquatic mammals. You may be fortunate enough to observe one in its watery habitat, or you may instead find evidence of the its presence. Either way, take time to contemplate the muskrat’s place in the panorama of living creatures and the adaptations that make it so successful.

Streamside Discoveries

As the high water levels of late winter and early spring subside, stream and lake margins become interesting tracking locations. Water is a magnet for wildlife, and visiting creatures leave the evidence of their activities along the shoreline. A great blue heron left the collection of tracks shown in the photo below. The feet of herons resemble the feet of songbirds, with one backward-pointing toe and three forward-pointing toes. But unlike most songbirds, the toes of herons don’t all meet at one point. There’s a left print (facing toward the lower right) in the upper left corner of the photo that shows this nicely. The junction between the backward-pointing toe and the inner forward-pointing toe lies to the left of the intersection between the two outer toes. Another way of saying this is that the two outer forward-pointing toes join a little to the outside of the center of the foot. The same asymmetry shows in the right track in the lower right corner.

The spotted sandpiper is another bird that patrols stream and lake margins. These small birds–about the size of a starling–search for invertebrates on the edges of streams, ponds, marshes, and other bodies of fresh water. Their tracks (shown in the next photo) reflect their erratic and meandering movements. The three forward-pointing toes are relatively symmetrical and diverge at wide angles. On the back of the foot there’s short spur oriented to the inside that may or may not make an impression in tracks. The left print just below the stick in the upper right corner shows the spur nicely.

Raccoons prefer comfortable surfaces so it’s no accident that the animal that left the tracks shown in the photo below stepped along a soft deposit of sand left by a recent flood. The raccoon moved from the upper right to the lower left, leaving tracks in the sequence right rear, left front, left rear, right front. The difference between the wider but tighter rear track and the narrower, more spreading front track is easily seen in the set of prints at the upper right. Raccoons habitually work the edges of streams and ponds where they find tasty shellfish, frogs, crayfish and other invertebrates. The pattern of alternating sets of hind and front tracks from opposite sides tells us the animal was moving at a pace-walk.

Mink are also in the habit of travelling along the margins of water bodies. The animal that made the tracks in the next photo was moving from right to left at a lope, and the track sequence is right front, right rear, left front, left rear. Like raccoons, mink have five toes on both front and rear feet, but it’s not uncommon for the impression of the inner toe to be missing. In fact the only print in the photo that shows a clear inner toe is the left front. This track also shows the middle pad protuberances (just behind the toes) and the heel pad (the small indentation behind the middle pad). Mink share a taste for crayfish, frogs and invertebrates with raccoons, and occasionally catch small fish. They’re adaptable predators and may also hunt for small mammals on the surrounding land.

The mink’s larger relative, the river otter, also leaves its tracks along the edges of ponds and streams, but for this creature it’s mainly a matter of convenient travel between feeding areas. I found the tracks in the photo below on the inside of a bend in a stream where an otter had taken a short cut across a large sandbar. The sequence of tracks is the same as that of the mink tracks in the previous image, and the family resemblance–both mink and otters are mustelids–can be seen in spite of the different substrates. Otters are more aquatic than mink and capture most of their food in the water.

When they’re not foraging in the water otters spend their time on conveniently accessed sites near the water. They roll on soft surfaces like grass and forest duff to clean and dry their fur, and they socialize with other members of their family group. They also leave notices in the form of scat to non-resident otters that the territory is occupied. The otter scat in the photo below contains crayfish shell fragments, but it’s also common to find scats containing fish scales and bones, or the slimy remains of frogs. Otters often use latrines where scat of various ages and contents can be found.

The beaver is another very aquatic mammal. In the photo below you see two beaver tracks, a right front (above) and a right rear (below), both facing toward the right. In the front track the four toes show clearly and the two heel pads appear as elongated grooves because the foot slipped in the mud. In the bottom part of the frame the three outer toes of the hind print show clearly but the two inner toes are obscured by the front print. As is often the case, the webbing of the hind foot doesn’t show. The size difference between the front and rear tracks is striking and helps us to understand why beavers are such strong swimmers. Beavers feed on the leaves, bark, and stems of woody plants year-round, but during the growing season the diet also includes aquatic plants, cattails, sedges, and forbs. Their tracks usually lead between the water and foraging sites on land, and signs of branches being dragged into the water are common.

Smaller–but just as well adapted to life in water–is the muskrat. Like the beaver, the muskrat has rear feet that are much larger than the front. In the photo below, the track farthest to the left is the right rear, and just to its right you see the right front. On the right side of the frame the left rear lies below the left front. Notice that the small inside toes of the front feet made impressions in both of the front prints. The muskrat’s front feet, like those of the beaver, are adapted for handling food items and building materials rather than for swimming.

If you wander along shorelines you may find muskrat latrines. These sites are usually located on logs or rocks that lie in the water but protrude above water level. In the next photo you can see a rock decorated with scat of varying ages, deposited as an announcement that the territory is occupied. Although muskrats occasionally consume animal foods they are primarily plant eaters, and their scats usually contain fibrous material.

This is just a sampling of some of the wonders to be found along the margins of lakes, streams, and marshes. There’s always something to be discovered, so next time you’re out and about, take a detour to check a stream edge or a muddy shoreline. Better yet–if you don’t mind some wading–try a stream walk. It could be just the thing on a summer day.

Raccoon Spring Fever

Winter is still with us, but the season is advancing and mild days are beginning to outnumber the cold ones. Raccoons have spent the frigid periods in a state of torpor, denned up in hollow trees, rock crevices, second-hand burrows, or perhaps under your porch. On warm days the animals emerge from their winter dens and roam about in search of food and mates. Their habitual use of a gait called the pace-walk gives their trails a unique and easily recognizable appearance.

In the pace-walk the tracks lie in sets of two, each set made up of front and rear prints from opposite sides. One of these prints generally falls ahead of the other (although they can be perfectly even). In each successive pair the sides of the front and rear tracks switch and, if they are uneven, the leading side also switches. In the photo above the larger hind prints lie ahead of the smaller front ones. The succession of tracks, starting at the lower right corner, is: left front with right rear, right front with left rear, left front with right rear, and right front with left rear.

Raccoons are not good at digging, and as long there’s a substantial snowpack they have difficulty getting at edibles in the leaf litter. But seeps and unfrozen streams are not only free of snow and ice–they also harbor tasty morsels like aquatic insect larvae, worms, snails, and other invertebrates. Seeps are likely to form during mild weather, and they’re usually found in the same places each year. Muddy tracks like the ones below tell us when raccoons have been visiting them.

There are two separate passages in the photo above, the upper one heading from left to right and the lower one going in the opposite direction. If you focus on the darker tracks in the middle of the photo, you can see the similarity between the patterns in the two photos. But in addition to being more irregular, the mud-on-snow tracks have a slightly different arrangement. In each set of two the larger hind foot touched down a little behind the smaller front foot. This, and the fact that the steps are shorter, tells us that the animal was going slower. The icy crust was probably slippery and the raccoon needed to be more careful with its footing.

As spring–and mud season–draws closer, raccoon tracks can be found in all sorts of wet places. When the photo below was taken a thin blanket of snow covered most of the landscape, but the silty stream margins were clear and unfrozen. The small tracks heading in both directions were made by minks, and the larger ones belong to a raccoon. There’s a pretty clear hind print near the right edge of the frame, but the other raccoon prints (one to its left and another toward the bottom of the frame) are distorted because the animal slipped in the mud. In fact the very weird track at the lower edge of the photo is actually two prints, one on top of the other. Apparently the heavier raccoon had more difficulty with its footing than the smaller minks did.

Here’s another trail made by a pace-walking raccoon on a nicely moistened sand road. The pairs of prints are a little closer together than the ones in the first photo, and the rear tracks fall slightly behind the front–both signs of lower speed. Maybe with its feet sinking slightly in the soft sand the animal chose to move more carefully, or maybe it just wasn’t in a hurry. On a mild spring day even a raccoon might feel like taking it easy.

The Graceful and Adaptable Mink

The mink is one of my favorite animals, so I’m always happy to find tracks like these, from a Tracking Club outing a few weeks ago. The marks made by the toes (5 on both front and rear feet) are small and oval or tear-drop shaped, and they form lopsided crescents around the middle pads. The claws may show as tiny pricks or as pointed extensions of the toes. The smallest toe lies on the inside of the track and farther back than the other toes, and it doesn’t always show. The mink that left these impressions was fidgeting around on a patch of stream side mud (the water is visible at the upper left) and the clear prints are mostly from the front feet.

But the beauty of mink tracks goes beyond the delicacy of individual prints–the trails that these animals make are equally fascinating. Here are the two front and two rear tracks of a mink arranged in a pattern often seen in mink trails. The first track at the lower right is the right front, and the last one at the upper left is the left rear. In the center of the photo the left front is on the left and the right rear is on the right. The animal was loping from the lower right to the upper left, and the order of footfalls was right front, left front, right rear, left rear. A mink traveling on stream ice a few winters ago left a string of similar four-print patterns. In the center of each grouping the left front print is slightly behind instead of ahead of the right rear, but otherwise they’re a good match with the previous photo, with the same direction of travel and order of footfalls. Notice how the four-print groupings are separated by spaces with no tracks–a characteristic of lopes and gallops. When I see trails like this I can picture the mink doing its easy, ground-covering lope, its spine curving and extending with each landing and take-off. I couldn’t find a video of a loping mink that I liked, but I did find one of a fisher (closely related to the mink) doing the same gait. Watch it here.

Stream edges are great places for finding mink tracks, especially if there are roots or debris piles where prey animals can hide. The patch of sand visible in the center of this photo captured the tracks of a mink that was hunting in the surrounding tangle of logs and branches, deposited by a big flood several years ago.

But minks are resourceful when it comes to finding food. Last spring I was walking by an old log landing and I noticed a drying mud puddle. I’m always interested in mud so I went over to take a look, and to my surprise found mink tracks around the edges. There was a small pond nearby, but otherwise not much water, and I didn’t understand why this place–just a big area of bared mineral soil with a few mud puddles–would interest a mink. But the tracks were plentiful and very clearly mink. In the photo on the right the mink tracks run from lower left to upper right, and the big prints in the middle belong to my dog. As I moved around the edge and pondered, the mystery resolved itself. A leopard frog leaped from a grass clump into the water, then another one jumped, and then several more. Some enterprising mink had discovered the puddle, perhaps just as the tadpoles were transforming into frogs, and made use of the easy dinner. There were still plenty of frogs left to spend their summer feeding in the surrounding forest, overwinter deep in the soil, and then mate and lay eggs in the puddle next spring.