Tag: beaver

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.

Beavers at Work

Some animals live among us almost undetected, and others leave evidence that is obvious and long-lasting. Beavers are a good example of the latter, leaving signs of feeding on woody plants and creating dams and lodges that may last for years. The featured photo shows a lodge made of mud and sticks and surrounded by protective moat of water. What we can’t see is the underwater entrance which leads upward to a dry, multi-level living area. In the upper left quadrant of the photo there’s a dam, seen from the upstream side. The freshly peeled sticks that decorate the lodge and the dam, and the water lapping right up to the top of the dam, indicate that there were beavers in residence when the photo was taken.

Beaver dams can be impressive structures. The next photo is a view of a dam from the downstream side. The heaped up sticks conceal inner layers of mud interlaced with more sticks. Beavers react to the sound of flowing water, and any leaks are plugged with mud and more sticks. As long as the dam is maintained, the water level stays high enough to keep the lodge (not seen in this photo) secure in its watery surroundings.

A little exploration around the edges of an active beaver colony will turn up additional signs. When whole trees are removed the only thing left may be a chewed stump like the one below. Wood chips scattered nearby show where branches were removed and the trunk was sectioned and dragged off.

Some logs may remain where they fell, but they seldom go unused. One such log is shown in the next photo, and it’s a nice demonstration of the beaver’s chewing technique. The horizontal row of small cuts along the edge of the bark shows where the upper incisors were anchored. The vertical grooves in the lower peeled part of the log were made as the lower incisors were drawn up toward the anchored upper incisors. And why all this chewing? To get at the living cambium cells, located between the wood and the outer bark. Although there are exceptional cases where other food is available (such as the rhizomes of water lilies), most beavers depend on the cambium of woody plants for survival when leafy vegetation isn’t available.

Many dams and lodges are used for several years in succession, and newly added sticks and branches stand out against the mud and older sticks. The residents of a beaver colony also create deliberate messages indicating their claim to the location. In the photo below you see mud that was dredged up from the bottom and deposited on top of a grass hummock to create a scent mound. Whatever is handy at the edge of the pond, whether it be mud, muck, or rotting vegetation, can be dredged up and carried to the shore to make a pile. The final touch comes when the beaver drags its anus over the mound and deposits urine and secretions from its anal glands and castor sacs. The smell is not unpleasant, but it’s hard to describe. It reminds me of a horse barn, but it has also been compared to musk, human sweat, cheese, fruit, leather, birch beer, or some combination thereof. Scent mounds are most often created in spring, and the distinctive odor can persist for weeks.

If ponds and small streams aren’t available, beavers take up residence in creeks and rivers. But these habitats are subject to regular flooding, and the volume of flow during high water would destroy dams and lodges, so river beavers make their homes in the stream banks, digging underwater entrances and excavating living spaces above water level. If beavers are living in a river you may find peeled sticks, cut stumps, and scent mounds along the riparian margin. Another good clue is tracks in silty or muddy stream margins.

The tracks in the photo below were made by a beaver walking from lower right to upper left. The large hind prints make a wide zig-zag, starting with the left rear in the lower right corner. As in other four-footed walking trails, there are two footfalls–a front and a rear from the same side–at each zig or zag, but the front prints are mostly covered by the larger rear prints. All, that is, except for the two tracks at the upper left. The larger print above is the right rear, and next to it, just below, is the much smaller right front. Some of the rear prints may remind you of the tracks of a large bird. That’s because beavers often touch down lightly or not at all with their two inside toes, so the outer three toes make the most prominent impressions. But the heel marks behind the toes (as well as the wide palm areas at the bases of the toes) tell us it was a beaver, not a bird.

Whether they’re pond beavers or river beavers, at some point the animals will have exhausted the local food supply and will be forced to relocate to a better situation. If dams and lodges are not maintained water levels will fall. Chewed stumps and peeled sticks will weather to dull gray. Even though they aren’t fresh, these signs will persist and provide clues to the past presence of beavers.

But an abandoned beaver pond can offer its own discoveries. The amount of material amassed to form a dam or a lodge can only be appreciated after the water is drained. The exposed mud can be a great place to find the tracks of other creatures. And old beaver ponds provide great opportunities to find beaver scat. The animals normally defecate in the water, so seeing fresh scat is rare. But once the water has drained out, scats may be left on the sloping inner sides of the dam and the perimeter of the pond. Beaver scat is oblong and can be anywhere from 1/2 to 1 1/4 inches in length. The fibrous content is easy to see in the photo below–a beaver needs to chew through lots of bark and wood to get enough nutrition.

I never get tired of visiting beaver sites, because there’s always something new to discover. Whether it’s the prodigious size of a felled tree, the clever way the animals engineer channels to make transporting logs easier, or a muddy stream margin decorated with the tracks of beavers commuting to and from work, it’s always fascinating. Beavers lead complex lives and show great ingenuity in dealing with their surroundings, and the signs they leave can give us a window into their cleverness and adaptability.

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.