animal tracking – Page 6 – Linda J. Spielman

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.

Looking On The Bright Side

The leaves are down, and the colorful spectacle of autumn is behind us. The forest has gone from a kaleidoscope of color to a narrow spectrum of browns and grays. But wait, what’s that pale streak glinting among the tree trunks? If you look closely you can see it in the center of the featured photo. Moving closer we can see that it’s a buck rub, bright wood laid bare by a hormone-driven male deer. This is rutting season for whitetail deer, and the bucks are roaming the landscape seeking receptive does. They leave their calling cards on living trees–anything from very young saplings to substantial trunks 8 inches or more in diameter. To make a rub the animal lowers its head and rakes its antlers up and down against the stem. Rough areas around the bases of the antlers work like files to abrade the outer bark down to the light colored sapwood.

The photo below is a close-up of the rub in the first photo. Rubs are usually between one and four feet above the ground, and their edges are often rough or stringy. Gouges made by the short tines near the antler bases are often present–look for them just above the debarked area. The brightness of the freshly exposed wood is what attracts our attention, and it may do the same for deer. But buck rubs also carry scent messages, deposited when the animal rubs its forehead against the newly bared surface. We’re not equipped to detect these chemical signals, but to a visiting doe they convey a wealth of information about the age, health, and even individual identity of the rub maker.

The light colored areas in the photo below have also been denuded of bark, but this wood was exposed by feeding rather than by rubbing. A porcupine climbed these yellow birch trees and chewed through the outer bark to get at the cambium, the living cells that produce both bark and wood during the growing season. There’s no mistaking this example for a buck rub, but porcupine chews are sometimes found close enough to the ground to be confusing. In both cases the light wood stands out against the bark, but there are several clues that distinguish rubs from chews.

Instead of a smooth surface, wood that has been exposed by porcupine feeding is textured by tooth grooves, and the margins are more irregular, as in the photo below. The tooth marks are just deep enough to reach the nutritious tissue, and are organized with a neatness that speaks of feeding efficiency. Along the margins of chews there are often tooth marks instead of the stringy fibers that mark the edges of rubs.

Beavers, like porcupines, rely on the cambium of woody plants for much of their winter diet. Being larger than porcupines, beavers’ wider incisors give their chews a more robust appearance. And rather than climb to access food, beavers bring the food down to their level by felling trees. The beaver that felled the log in the photo below stood on its back feet to feed, anchoring its upper incisors in the bark and drawing its lower incisors upward to scrape up the cambium. It moved systematically along the log, leaving the row of shallow upper incisor digs in the bark and the longer lower incisor marks below them. Like the porcupine, the beaver penetrated just deep enough to scrape up the nutritious cambium.

Not all bark chewers show this kind of efficiency. The sumac stem below was chewed by a rabbit, and its ragged appearance contrasts with the more orderly work done by beavers and porcupines. Rabbits only feed on small stems, and their chews show varying depths of penetration with projecting splinters of bark and wood. Like beavers they are limited to what they can reach from the surface they’re standing on, but if there’s a deep snow pack or heavy snow that bends branches down, rabbit chews can be found in some surprising places.

Here’s another kind of feeding that might catch your eye in the autumn woods. Woodpeckers worked on this standing dead tree to get at the insects in the outer layers of wood. The beak strikes left pits, partially lifted slivers, and gouges (best seen on the right edge of the tree). This kind of woodpecker work can be located at any height, and may even be found on downed logs, but unlike the previous examples, it only occurs on dead trees.

Here’s a final example of eye-catching brightness. As the weather gets colder, squirrels leave their leafy tree-top dreys and make nests in hollow trees or other protected places. They gather fibrous bark for nest lining, and in the process, leave freshly debarked wood for us to find. The dead, fallen branch in the photo below was stripped of its fibrous inner bark by a squirrel. Although there’s a vague resemblance to a buck rub, the position of the branch and its non-living status indicate squirrel work rather than deer.

When squirrels harvest fiber from woody plants they may leave another clue. In the photo below you can see the paired marks of a squirrel’s incisors. Much of the bark removal is done by pulling up long strips, but occasionally the squirrel leaves a bite mark as it grasps the bark with its teeth.

Squirrel stripping is also found on living stems–I’ve seen it on honeysuckle and red cedar–and these are more likely to be mistaken for buck rubs. But areas shredded by squirrels are often in places a deer wouldn’t be able to reach, higher on a trunk, within multi-stemmed shrubs, or on stems guarded by projecting branches. Deer prefer sites with straight stems and unobstructed approaches, and any small branches or twigs are usually broken off by the vigorous action of making a rub.

I love this time of year–the leaves are down, and I can see for greater distances through the trees. Many signs of animal activity are hidden by fallen leaves, but others have become more visible. And every once in a while a bright patch shining among the duller tones draws me in and opens up a new and interesting discovery.

Bounty From Above

The season is turning, and red squirrels are obsessed with gathering food stores for the winter. They will rely primarily on the cones of spruce, fir, and pine–and to a lesser extent on larch, eastern hemlock, and white cedar–for survival over the coming months. The squirrels’ preparations for the lean times ahead leave plenty of evidence. In the photo below the ground is littered with red pine cones. A few brown cones that fell the previous year contrast with the green of this year’s crop. When stored in a humid environment the tightly closed green cones will last through the winter without opening, preserving their precious seeds until a red squirrel pulls them apart to get at the nutritious nuggets inside.

The next photo was taken in a stand of Norway spruce, a tree that is native to northern Europe but was widely used in reforestation projects in the US during the twentieth century. Some of the trees in these plantations are large and produce copious crops of cones. The cones’ large size–some as long as eight inches–means they are a bonanza of food for red squirrels.

You can see another harvest in the photo below, this time the cones of white pine. Again, it’s the largest trees, the ones that tower over the rest of the forest, that produce the best crops of cones and attract red squirrels to harvest them.

These arrays of fallen cones don’t usually last long. After working in the tree tops to drop a supply of cones the squirrel descends and transports the bounty to an underground storage space, known as a larder. A red squirrel typically has a number of larders, often made by enlarging the natural spaces that form around large roots. Rock crevices and hollow trees may also be used, and cones are sometimes stored under fallen trees or even in abandoned buildings. Green cones stay tightly closed all winter and well into spring in these humid spaces.

The white pine cones shown in the next image were also nipped by a red squirrel, and these cones probably look more like the ones you’re used to seeing. There must have been an interruption before they could be transported to a storage cavity, because they’ve dried out and released their seeds. Our weather has been dry lately, so drying may have happened unusually quickly, making the cones useless for winter food. So if the seeds were released when the cones opened, where are they, you ask? Such a concentrated serving of edibles wouldn’t have gone unnoticed by birds and small mammals and would have been rapidly consumed.

I was curious about how the squirrels detach cones from branches. I imagined a a lot of yanking and chewing, which should have left tooth or claw indentations somewhere around the sides of the cones. But when I looked for marks, all I could find were small bits of exposed wood at the attachment sites. The photo below shows the lighter separation areas at the bases of some of the red pine cones I examined. On Norway spruce and white pine cones it was the same– all I saw were small separation wounds at the bases.

I realized I needed to see how cones are attached to twigs, and what I found suggests that nipping cones is pretty straightforward. In the next photo you see a red pine cone attached tightly to a twig. A squirrel need only bite through the attachment point by inserting its tiny incisors into the angle between the cone and the twig. This would produce a lighter colored spot at the separation point like the ones I observed on the dropped cones.

I’ve never seen this happening (how I would love to levitate to the top of a tree and watch!) but I did find a video of a red squirrel harvesting cones from a western pine, probably a ponderosa pine. You can see it here. (The clearest view starts at 2 minutes and lasts about a minute.) The squirrel perches on the branch and works from the back side of the cone, occasionally using its front feet but mostly just gnawing at the connection between the cone and the branch until the cone falls.

Finding the evidence left by these frenetic little creatures isn’t hard–just pay attention to what’s on the ground whenever you pass under conifers. You’re most likely to find signs of harvesting where there are middens (piles of discarded cone scales and cores) from previous years, since resident squirrels tend to keep the same territories year after year. And sound may guide you to a harvesting site. A falling cone lands with a thump; the bigger the cone the louder the thump. If a falling cone hits branches on the way down you’ll hear some plunks and bonks followed by a thump. Follow your ears toward the sounds and you’ll probably find nipped cones scattered on the ground and a red squirrel chattering angrily at you from high in the tree.

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.

River Otters: Living in Two Worlds

I’m fascinated by river otters. Well, I guess I’m fascinated by all animals, but otters hold a special appeal. We humans can relate easily to their playfulness and sociability. The otter pictured below was photographed at the Lindsay-Parsons Biodiversity Preserve in Tompkins County, New York. This expanse of ponds, meadows, wetlands, and forests is one of many protected areas managed by the Finger Lakes Land Trust. It’s open to the public and is a great place to watch otters. And even if an otter doesn’t show itself while you’re there, you’ll probably find evidence of its presence in the form of tracks, scat, or resting areas.

Photo by Scott Levine, Finger Lakes Land Trust

Scat (sometimes called spraint) is probably the most obvious sign left by otters. Their diet of fish, crayfish, crabs, freshwater and saltwater mussels, and even small mammals and birds brings with it indigestible parts which end up in fecal material. In the center and upper left of the photo below you see formed scat containing crayfish shell fragments held together by finer material. The roughly tubular shape of these deposits indicates that they are relatively recent. Under the influence of rain and weathering otter scat readily disintegrates into scatterings of the more visible parts, like the fish scales at the lower right.

Scat is an important means of communication among otters and is usually placed in significant locations, such as on trails between bodies of water, near dens, and at resting areas. Popular locations may accumulate scat of varying ages, and the collections become especially large when several otters are using the area. In the photo below large piles of scat lie in the lower middle part of the frame, and smaller deposits can be seen both uphill and downhill. The entire area has a trampled look, and in the upper part of the photo, slightly to the left of center, there’s a slight hollow that is relatively bare of debris. It looks like both a comfortable resting spot and a good lookout over the river below.

Otters are fastidious about keeping their fur in good condition, and in addition to grooming, the animals do a lot of rolling. This dry wash technique removes both grime and water, helping to maintain the insulating qualities of the coat. Rolling spots may be in conifer duff, grass, soil, sand, or even in snow. The animal that made the roll in the photo below came out of the water from the ice hole at the left. Around the edges of the roll the snow was pushed outward by the otter’s feet, and in the center it was flattened as the otter writhed on its back. There are some nice tail marks at the upper right. After it rolled the otter went right back into the water, leaving a few tracks and a body slide on the left side of the photo. There’s a great video here that shows the playful energy of a rolling otter.

Sliding is another favorite otter pastime. While the animals will occasionally slide downhill on grass or mud, sliding reaches its apogee in snow. On good snow an otter can slide down hills, on level terrain, and even up slight inclines, using its feet only when needed to keep the joyride going. And joyride isn’t an exaggeration. Otters sometimes make repeated slides, turning around and going back time after time to enjoy another go.

And then there are tracks. Otter tracks are similar to those of other members of the Mustelid family, with five toes arranged asymmetrically on both front and back feet. The animal that made the tracks in the photo below was moving from lower left to upper right. The first print at the lower left is the left front, the next is the left rear, then comes the right front and finally the right rear. This pattern of front-hind-front-hind, and the space separating the first group of four from the next group, are typical of the lope, the otter’s preferred gait. Another cogent detail is the relative sizes of the prints. The rear tracks (the second and fourth in each group) are larger than the front tracks, a feature that distinguishes otter tracks from the similar-sized tracks of the fisher. The otter’s hind feet are webbed, and the toes can spread widely to make optimal use of the webbing when swimming. There’s a hint of webbing in the right rear print in the first group shown below, but webbing doesn’t always show in tracks. And as you can see from the photo, tail marks may not be present. In fact they’re rare unless the animal is moving in deep snow.

When otters are in the area they usually leave plenty of evidence, but you may miss it unless you look in the right places. These include silty or sandy shorelines, grassy or forested stream banks, ice-covered ponds and streams, beaver dams or artificial dikes, peninsulas, and trails or elevations between bodies of water. As you observe these places you’ll get a feel for convenient travel routes, good rolling spots, and preferred resting areas. Bluffs of banks with easy access from the water and padded with soft forest duff are always good places to check and often have tracks, scat, rolls, or other evidence of otter activity. The places otters choose are often the places I’d pick for a pleasant lunch stop. Looking down on a river from such a spot I can imagine an otter emerging from the water, loping up the bank, and making a quick check of the situation. Perhaps it examines scat left by another member of its family group and adds some of its own to the collection. Or maybe it enjoys a short rest and a good roll before returning to the water for more foraging.

The aquatic part of an otter’s life is mostly hidden from us, but as soon as it leaves the water an otter leaves evidence of its life on land. Reading those messages can give us glimpses into the lives of these truly remarkable animals.

Walking the Rails

When I was a kid I used to enjoy exploring the woods and fields near my home, and one of my routes involved travelling along a seldom used railroad line. The rocky bed that supported the ties and rails was hard to walk on, and the spacing of the ties was just a little different from my natural step, so I often walked on one of the steel rails. Recently I found myself doing the same thing–walking along a seldom used railroad line and attempting to keep my balance as I walked on a rail. As I stepped carefully along I saw some peculiar muddy smudges on the rail ahead of me.

I thought at first that someone with muddy sneakers had been there ahead of me. But the marks didn’t look like the tread pattern of a shoe, and some of the groups of muddy spots seemed to form zig-zags rather than the centered prints that a person would make. My puzzlement turned to delighted comprehension as I noticed more details. The zig-zag sections were separated by areas that were smeared or had a jumble of muddy marks, such as the the area at the top right in the photo above. It was as if a walking animal had occasionally lost its balance and shifted its steps to keep from falling off the rail.

In the clearest impressions, arrays of small mud spots seemed to form half-circles around central clusters of smudges, as in the two photos below. The more I looked at them, the more the outer marks looked like toes and the inner clusters like middle pads. And those half-circles of widely separated toes, spreading across most of the top of the rail, could only have been made by an opossum.

Compare the images above with the photo of opossum tracks in mud (from a different opossum encounter) below–the left front track at the upper right and the left rear track below. Notice how the widely spread front toes encircle the middle pads; the upper two middle pads show as triangular impressions and the lower two as faint roughenings of the shiny mud surface. Four toes of the hind print point toward the upper left and the innermost hind toe–probably superimposed on the innermost front toe–points toward the right. The front print is a pretty good match for the mud-on-steel prints in the photos above.

Here’s another shot (from last winter) of opossum tracks, the left front on the right and the left hind on the left. The perfect tracking snow recorded the triangular to oblong middle pads of both front and rear feet beautifully. In the front print the position of the middle pads inside the circle of toes reproduces the positioning of the inner clusters and outer circles of mud marks in the tracks on the rail.

The positioning of the rear feet of a walking opossum is often erratic, and the animal that walked on the rail left many rear tracks that were smeared, distorted, or partly missing. In the photo below the middle pad area of the left rear foot (on the left side) made the large smudge behind the left front print (on the right), and the four outer toes of the rear track left spots and smears on the sloped upper edge of the rail. The lack of precision in the placement of its rear feet may have caused some missteps as the opossum attempted to balance on that three-inch rail.

Putting it all together, the whole scene made sense. I found the muddy slough the possum had crossed, coating its feet in ooze, before it climbed up onto the railroad bed. There were sloppy smears and spatters on the rocky shoulder of the railroad bed, and on the ties where it had first stepped onto the rail. The zig-zag pattern of the walking gait was occasionally punctuated by sections with extra steps and smeared mud where the opossum had struggled with its balance. (What would it look like if a more precise walker–like a cat–had left muddy prints on a rail?) At each step mud was transferred from the opossum’s feet to the rail, and the tracks grew fainter and finally disappeared. I continued in the same direction toward a road bridge which crossed the railroad line. Under the bridge there was a wide, dusty area, and when I stepped away from the tracks to investigate I saw a recently made opossum trail. Could it have been the same animal? I can’t be sure, but I feel a kinship with the opossum that made the muddy tracks. In spite of our balance problems we both found walking the rail to be a good way to get where we wanted to go.

Getting to Know Porcupines

I’ve been thinking about porcupines. There are porcupines in central New York where I live, but they’re not common, so in that region (unlike in the Adirondacks) I don’t often encounter their tracks. But this spring we had some late April snowfalls, and on two different occasions I was surprised and excited to find porcupine trails. In the photo below (direction of travel from right to left) you can see the left front and left rear tracks. The hind track (on the left) shows the flattened sole area of the foot nicely, with the marks of the claws to its left. The smaller front print lies to the right but isn’t as clear because the thin snow fractured in the sole area and three of the four claw marks were covered by the hind print.

Those meager April snowfalls weren’t ideal for recording clear tracks, so I’m including a more revealing photo of porcupine tracks that I took a few years ago in the Adirondacks. There was a light skiff of snow on a dark, icy base, and the soles and claws can be seen clearly. Again, the tracks are left front and hind, and the direction of travel is toward the upper left. In the rear print (on the right) the sole is larger but the claws are shorter than in the front print (on the left). If you look carefully at the front track you can see the faint imprints of the front toes (which usually don’t show up at all) just behind the dark holes made by the claws. And those streaks that run toward the upper left from the front claw impressions are drag marks made by the claws as they came forward when the foot was lifted.

So what if there’s no snow? Following trails may not be an option, but porcupines leave plenty of other evidence of their presence. Their winter diet includes the inner bark of trees, both conifers and hardwoods, and the buds and leaves of conifers. Scenes like the one pictured below (on yellow birch) show how efficient a porcupine can be at removing the cambium tissues of living trees. And this kind of evidence lasts long after the actual feeding was done. Small debarked patches high in hardwoods (but not conifers) could also be due to squirrels, which may turn to bark feeding when other food is scarce. However, the amount of exposed wood in the photo below is more than a squirrel would be able to achieve.

To get at tree buds or leaves a porcupine climbs high into a tree (where the most vigorous branches are), bites off twigs, eats the buds or leaves, and then drops the twigs. The photo below shows a scattering of nip twigs which accumulated on the ground as a porky fed in the hemlock tree above. When porcupines feed on the swelling buds of sugar maples in early spring, or on acorns in late summer, they harvest and discard the twigs in a similar manner.

But twigs and branches can fall with no help from porcupines, so how do we know whether a porky was the culprit? The first clue is the relatively even sizes of nip twigs (mostly 1 1/2 to 2 1/2 feet), compared with the wide range of sizes when wind or ice damage is the cause. Another clue is the appearance of the separation site. Randomly broken branches and twigs have ragged, irregular ends. The photo below shows the clean, angled cut found on a red oak twig that was nipped by a porcupine.

To get to feeding spots high in the canopy a porcupine must climb trees, and on trees with light bark, like the aspen in the photo below, climbing marks are very visible. Aspens are sought out by porcupines in spring when the leaves are young and easily digested, and preferred trees are often visited several years in succession. Bears also climb trees to feast on young leaves, nuts, and fruits, but the spacing between porcupine claw marks, between 1/4 and 3/4 of an inch, is much closer than the spacing in climbing marks left by bears.

Porcupine dens are another unmistakable sign. Unlike many other animals, porcupines defecate in their sleeping areas, and when scat piles up they simply plow through it or push it out of the way. The trunk of the sugar maple in the photo below had a hollow space which served as a porcupine den, and the waterfall of scat which fell down from it is evidence of an extended period of occupancy. Porcupine scats are cylindrical to kidney-shaped, and they can also be found among the nip twigs dropped from favored feeding trees.

In spite of their prickly defense, porcupines are preyed upon by most medium-sized carnivores. I found the coyote scat in the next photo last winter, earlier but in the same general area where I found the nip twigs and the tracks in the April snow. The coyote could have been responsible for the porky’s death, but it’s also possible that the initial killer was a fisher, and that the coyote scavenged the carcass later. The quantity of quill fragments is surprising and makes me wonder whether any quills entered the coyote’s body.

By now porcupines have left the mature forests and moved to more mixed habitats where they can find the growing herbaceous shoots and leaves, cattails and other wetland plants, roots, tubers, and fruits that make up their spring and summer diet. There are lots of other animals which consume the same plants, so unless you actually see a porcupine having a meal it’s hard to recognize the signs of summer feeding. But if you’re alert you may find long-lasting evidence of their cold weather activities.

Logs

Living creatures see the world in terms of significant objects. We humans are no exception–for us significant features would be such things as chairs, doorways, computers, streets, buildings, picnic tables, traffic lights….you get the idea. For wild animals rocks, thickets, streams, cliffs, and trees come to mind. And then there are logs–items that we usually ignore unless we’re looking for a place to sit. Downed logs are important to many animals in many different ways, and the evidence is often plain to see.

A chipmunk sat on the log in the photo above to eat a red oak acorn. In order to get at the edible meat, the animal tore narrow strips and small chunks from the outer covering. Logs serve as feeding platforms for many small rodents, including red and gray squirrels, and the leftovers often reveal who the diner was. When squirrels feed on red oak acorns, the shell fragments left behind tend to be larger than those discarded by chipmunks.

The log above was used by a red squirrel feeding on red pine cones. As the squirrel fed it dropped the cone scales and cores on the ground in front of the log to create a large midden. Red pines are self-pruning trees and don’t offer many branch perches, so although red squirrels prefer the safety of branch perches, they sometimes need to use more earth-bound objects. Logs, stumps, and rocks can offer a good view of the surroundings and allow the animal to detect danger.

And how do we know it was a red squirrel? Although gray squirrels do sometimes eat conifer seeds, they don’t store them the way red squirrels do, and they never feed on enough conifer cones to create middens the size of the one in the photo.

Tracks on logs tell us that they can also serve as travel routes. Of course we need snow to see this kind of evidence–the light snowfalls of early winter and early spring often show the prints of animals that walked on logs. The coyote that made the tracks in the photo above found the log to be a convenient route through an area obstructed by branches and undergrowth. Walking on logs may also be quieter since leaves and debris can be noisy, even under a layer of snow. Another advantage of walking on logs is a better view. The greater elevation helps prey animals to detect danger, and predators to detect prey. I’ve found many different tracks on logs–the list includes squirrels, white-footed mice, chipmunks, raccoons, bobcats, bears, red and gray foxes, coyotes, fishers, minks, and weasels.

Logs offer these same advantages when there’s no snow, so we can be sure that animals also walk on logs in warmer weather. Without snow their tracks are difficult to detect, but we may still find evidence of their passing. A long-tailed weasel left the scat shown in the photo above on a mossy log. The scat was not quite 1/4 inch in diameter and contained hairs from a small mammal.

The logs in the photo at the head of this article are ones I visit regularly, and they often accumulate the scat of several different kinds of animals. This suggests that they have some special importance, but I’m not sure exactly why. The log in the foreground bridges a low, rocky gully, but the more distant one lies on more level ground. Both logs are large, but there are other logs nearby that are as big or bigger and don’t accumulate scat. Whatever the reason, we can be sure that each species that travels those logs takes note of the messages left by other creatures.

In addition to serving as perches, travel routes, and bulletin boards, logs may be a source of food. This log was torn open by a black bear in search of the grubs that were living and feeding in the rotting wood. Bears are not the only creatures that find food in logs–skunks, raccoons, and woodpeckers also open logs in search of edible morsels. But the size of the fragments and the distance to which they were thrown could only have be the work of an animal as powerful as a bear.

Have you heard a grouse drumming this spring? At this time of year ruffed grouse are looking for mates. The males seek out large logs, and once they find a log that offers a stable and well elevated surface they send out a kind of drumming sound with their wings. The low sound travels long distances, and the elevation of the log gives it even more range. Females are drawn to the sound, and if they’re impressed they will mate with the male. In the photo above I’m perched on a grouse drumming log, taking a photo with my old SLR camera. In front of me on the log you can see several grouse scats.

Whether they’re dinner tables, highways, message boards, pantries, stages, or even just obstacles, logs are significant objects for inhabitants of the natural environment. The evidence they present can reveal unseen dramas in the lives of animals. So before you sit on that log, take a look at it. You might be rewarded with a message that opens a window into the life of a wild creature.

Incisive Communication

Communication is an essential part of life for all animals. For squirrels and their kin spring is a time of intensive communication, as they select nest sites and prepare to birth and raise young. And the leafless canopy of early spring affords good visibility, so it’s a great time to spot the messages left by these animals.

The strong, sharp incisors possessed by all rodents–two in the upper jaw and two in the lower–are perfect tools for inscribing messages. In the photo below bright gouges show where a squirrel bit into the sides of a narrow cleft in a tree. The cleft was at eye-level, so the reddish marks of the animal’s incisors were easy to see. After making the bites the animal may have rubbed its cheeks on the bark to leave a scent message. Squirrels have a well developed sense of smell, so the saliva left in the bites and the scent from the cheek rubbing may have been even more meaningful than the visual marks.

Squirrels also create “stripes” on tree trunks. In the next photo gray squirrels–probably more than one–made many bites in an elongated zone between four and six feet off the ground along the trunk of a white oak. If you look carefully you’ll see that the individual bites vary in color, from bright reddish (the most recent) through grayish red to dull gray (the oldest). The varying age of the bites indicates that this stripe has been worked in the same way over several years. The individuals making the bites probably also did some cheek rubbing, so the bark would have been perfumed with an abundance of scents.

Marks like the ones pictured above are usually found in the general vicinity of nesting or feeding areas, but sometimes the bites seem to indicate a claim to a particular nest site. I’m not talking about summer nests, the leafy dreys seen high in the branches of large trees. In areas with cold winters, both winter and birthing nests are located in safe, weather-proof sites like hollow trees or underground cavities, and the supply of good sites may be limited. The hole shown in the photo below was located about 20 feet up in a large tree. There was probably a perfect nest cavity inside–the opening looked well used, and the varying intensity of the bitten areas suggested that the site had been used for at least several years. By marking the opening, the resident squirrel was able to establish ownership of its chosen refuge.

Squirrels are not the only creatures associated with tree holes. The openings shown below were made by pileated woodpeckers. From a distance the bright margin of a woodpecker hole may look like the chewed edges of a squirrel hole, and the size and shape may be about right. But it’s easy to tell that these holes are not squirrel holes. The first clue is their rough, splintery margins. Another clue is the number of holes–in this case there were five similar openings distributed along the trunk. These holes were made for feeding, and they’re distributed up and down the trunk because the insects the woodpecker was seeking–probably carpenter ants–had colonized much of the tree. Woodpecker holes are often more irregular in shape, and when that’s the case it’s easy to tell that they weren’t chewed on by squirrels.

Whether a mark was made by a red or a gray squirrel is often hard to determine–both are known to make stripes along trunks, and both probably mark the entries to nest cavities. Flying squirrels may mark in similar ways, but I haven’t been able to find any mention of that in the tracking literature and I don’t have any examples to share. If anyone knows the location of a definite flying squirrel nest hole, I’d love to hear about it.

Chipmunks tend to use underground refuges rather than tree cavities, and I haven’t seen anything in the literature about chipmunk marking. But a few weeks ago I came across the hole in the photo below, located a little above my head in a small tree. It puzzled me at first because the chews looked rougher and more irregular than the typical squirrel chew. But the mystery was solved when I stood on my tip toes to get a closer look. Out of the hole came the frantic chittering of a chipmunk. The animal sounded so upset that I left quickly, but I thanked it for showing me what a chipmunk can do with its teeth.

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.