With the coming of spring nature is breaking its winter dormancy, but we’re still a long way from the bounty of summer. In some years the food stores that carried squirrels through the winter are depleted by the time spring comes around, and when this happens the new season may bring food stress instead of abundance. This is especially true if there’s a new litter of young to raise. But over the last month or so I’ve been finding evidence that squirrels are still making use of winter’s leftovers. Digs like the one in the photo below show where an edible item was extracted. I’m confident that this was a recent dig, because the leaves around the dig were still pushed up and the soil was freshly disturbed. If this were an old dig the heavy rains we had earlier in the month would have flattened the leaves and washed the soil back into the hole.
Without further investigation it’s hard to see what the squirrel was after. When I carefully removed the leaves (as shown in the next photo), I saw not only evidence that this was a fresh disturbance but also evidence of what was removed: a firm-walled cavity that was the perfect shape of an acorn.
More proof that buried acorns are still being utilized by gray squirrels is shown in the next photo. The brightness of the acorn remnants indicates that they were not more than a few weeks old when the photo was taken in mid-April.
Instead of acorns, red squirrels rely on conifer seeds for survival over the winter, and in many locations they are still making use of the stores of cones that were gathered last summer. A few weeks ago I found a spot (shown in the next photo) where a red squirrel had extracted the seeds from a red pine cone. The bright colors of the cone core and cone scales show that the feeding activity occurred recently. Additional corroboration of recent feeding comes from weather observations. In early April we had several intense downpours, and if the cone remnants had resulted from winter feeding the heavy rain would have washed them off the log.
I’ve noticed lots of recent feeding on white pine cones this spring. In the next photo you see a midden at the base of a large white pine. The feeding perch was on the branch at the top center, and entrances to the underground storage areas can be see a little below on both sides of the feeding perch. Again, the brightness of the discarded cone scales suggests recent feeding.
A close-up of one of the tunnel entrances shows dry material that was brought out of the storage space as the resident red squirrel retrieved stored cones–more evidence of recent activity.
Even if winter leftovers are still available they may have suffered some deterioration, forcing squirrels to seek supplemental foods. A squirrel harvested the boxelder twigs shown in the next photo and fed on the buds. The end buds are missing from the twig on the left, and several lateral buds were taken off of both twigs. Why weren’t all of the buds eaten? Perhaps because there were so many buds and twigs available that the squirrel could be haphazard in its feeding.
Grubs are common in grassy areas, especially in suburban lawns, and they can be important in squirrels’ spring diet. I found the dig shown below in my back yard.
Squirrels are also known to eat conifer needles. In the next photo you see white pine needles that were fed on by a red squirrel. Compared to acorns and grubs, conifer needles don’t seem very nutritious, but they may fill a need for nutrients that are otherwise lacking.
The rising sap of deciduous trees is another source of calories, and it usually becomes available just when squirrels need an energy boost. A red squirrel tapped the black birch sapling shown in the photo below. There’s a fresh bite (with a slight greenish hue) about midway up the stem, and old bites from previous years can be seen above and below. There’s another fresh bite along the side of the stem near the top. Squirrels are expert sap harvesters and use an efficient method to extract the maximum benefit. Rather than lap up the dilute sap, the clever animals let the water evaporate and return the next day to eat the concentrated solids.
Some foods may become less available in spring, but other dietary options are simultaneously becoming more available. Squirrels are flexible in their eating habits, and this is the perfect time to observe their ability to make use of a wide range of foods.
Perches–they’re important to wild creatures for many different reasons. The gray squirrel in the opening image (from yardandgarage.com) is using a perch as a feeding site. The next photo shows a Norway spruce whose dead lower branches provided feeding perches for a red squirrel. You can see how the piles of inedible cone cores and scales accumulated under the branches the squirrel perched on. These accumulations are called middens, and they can build up over time into substantial mounds.
Favorite perches often show signs of usage. The red squirrel that used the perch shown below left a cone scale and a number of opened seeds, some with wings still attached.
Red squirrels may mark perches by biting them. In the next photo you see a Norway spruce branch that bears the distinctive paired incisor marks made by a red squirrel. The lower branches of conifers are usually dead, so these marks don’t heal over and may last quite a while.
In the next photo you see a discovery I made during summer a few years ago. The Norway spruce cone crop that year was early and abundant, and a red squirrel had left a cone core, stripped of its supply of edible seeds, resting on the perch it had used. And in case you’re wondering, no, I didn’t put it there, it was all the squirrel’s doing. The scales that dropped as the squirrel fed can be seen on the ground at the base of the tree.
The photo below shows an unusually well elevated feeding perch used by a gray squirrel.
In the next photo you see what I found on top of the log: the remains of an acorn the squirrel had fed on.
Here’s a perch used not for feeding but for food storage. A gray squirrel lodged a black walnut in the crotch of a honeysuckle branch. I’m not sure what the squirrel’s motivation was–perhaps it was to keep the walnut away from other squirrels.
A perch doesn’t need to be overly high to be suitable. In the next photo you see a log used by a squirrel–it could have been a red or a gray–feeding on a white pine cone.
Rocks can also make good perches. Last August a red squirrel harvested young larch cones and brought them to the rock shown below for consumption. Where rocks or logs are available they are preferred over ground level feeding sites.
But food isn’t the only thing drawing animals to perches. A red fox balanced on the log in the next photo in order to deposit its scat. Scat is important in intraspecies communication, and wild canines prefer to leave their scat in conspicuous positions. Sometimes this requires a little acrobatic ability to position the scat just right.
One of my favorite spring experiences is hearing the drumming of ruffed grouse. Males in search of mates perch on logs or other raised features and beat their wings to produce a resonant booming sound. They prefer platforms that are unobstructed and raised well off the ground. You can see a spot in the center of the image where the bark was dislodged by the drumming bird.
Perches can also be used as observation posts. In the next photo you see a mound of earth thrown up by a falling tree. There were tracks–they were barely visible so I didn’t include a photo–going up the side. The size of the impressions suggested a fox.
On top of the mound (shown in the next photo) there were obvious signs of disturbance, showing that it had been used as a perch. The fox would have sat quietly while it listened, looked, and sniffed for signs of prey animals.
We seem to have circled back around to the topic of food, so here’s my last example of a feeding perch. A black bear climbed the beech tree in the photo below and pulled a nut-bearing branch inwards until it broke off. The bear consumed the goodies, pushed the branch aside and pulled another one inward until it broke. The discarded branches formed a tangled cluster, and the bear might even have stood on the growing mass of harvested branches as it continued to pull more branches in. These branch clusters are known by the somewhat misleading term bear nests, although they have more in common with squirrel middens than with nests. With healthy beeches becoming less abundant, bear nests in beech trees are harder to find than they used to be, but the same kind of sign occurs in apple, black cherry, serviceberry, and oak trees.
Wild creatures know their territories in minute detail, and they’re familiar with all the best perches. The attributes of a perfect perch vary somewhat with the specific animal and situation, but safety and accessibility are always important. The location also needs to be appropriate to the animal’s purpose, whether it’s to consume food, to find food, or to advertise its presence. If we stay alert for perches we can begin to understand what makes a good perch and what they can tell us about the lives of the animals.
As the leaves come down it’s easier to see into the forest canopy, and the summer nests of squirrels become more visible. The photo below shows a gray squirrel nest, a leafy structure located on a supporting branch junction. Also known as dreys, gray squirrel nests are usually located in crotches or branch junctions of deciduous trees. To build a nest in a tree, a squirrel constructs a framework of twigs and stuffs it with leaves, then makes an entrance hole and hollows out the inside of the structure. A lining of soft material such as moss or dry grass is added, and a second opening is made to serve as an emergency exit. Dreys differ from bird nests in being roughly spherical, with an enclosed interior space connected to the outside through small openings. Bird nests also lack the leafy appearance of gray squirrel nests.
Red squirrel nests are similar but are likely to incorporate a variety of materials in the outer layers. They are also more likely to be built in conifers. The next photo shows a red squirrel nest located in a larch tree. Twigs and grasses form the lower part of the nest, and fragments of plastic sheeting cover the upper part.
The nest shown above was easy to see in winter when the larch was leafless, but nests located in evergreen conifers are harder to find. The one in the photo below was tucked up against the trunk of a Norway spruce tree.
Here’s another red squirrel nest which was constructed in the crotch of a Scots pine.
There’s not nearly as much information available on flying squirrel nests, no doubt because flying squirrels are nocturnal and not as easily observed as gray and red squirrels. Mark Elbroch, in Mammal Tracks and Sign, Second Edition, reports that flying squirrel dreys are smaller than red or gray squirrel nests and are made of grasses and other fine materials rather than leaves.
In more southern climes dreys may suffice for winter lodging, but in our area squirrels move into more sheltered accommodations when the weather gets cold. Human structures are used where they are available, but hollow trees are the preferred choice for forest-dwelling squirrels. Nests enclosed in protective walls of wood and lined with insulating materials provide warmth, protection from the weather, and security. But is there any way for us to know which tree houses a nest? It’s not always possible, but there may be clues. The tree in the photo below must have had a good nesting space because it had been marked with a few bites. We recognize the bites visually, but the persistent odor of the resident squirrel’s saliva is more important to other squirrels, signaling that the space is occupied.
Red, gray, and flying squirrels all make winter nests in hollow trees. If the opening is quite small it’s probably not occupied by a gray squirrel, but beyond that, the size of the opening doesn’t tell us much about who the occupant is. I’ve found marked openings in trees where gray squirrels are absent and red squirrels are common, and also in areas where the reverse is true, so I believe that both species create bite marks to claim nest sites.
Bite marks can be sparse, like the ones above, or plentiful, like the artistic creation in the next image. I suspect that the double ring of bites was created because the owner felt threatened by the presence of other squirrels.
Nests in hollow trees continue to be useful well into spring as birthing dens. But although well protected from the elements, they have a drawback: there is usually just one entrance. In the next photo you see some nest lining that was removed from a nest and ended up in a pile on the ground. This would only have happened if a predator had raided the nest and, in the process, pulled the nest lining out. It could have been a fisher, or possibly a raccoon. Both are good climbers and fishers are considered to be specialists in squirrel predation. At any rate, nests in hollow trees are not completely safe.
In addition to clues about predation, the photo above shows us what nest lining looks like. To make this material, squirrels harvest bark and process it into finely divided strands that can be stuffed into tree cavities to provide insulation. The bark usually comes from dead branches, but may also be gathered from living stems of plants such as honeysuckle or white cedar.
The next image shows a dead striped maple branch that was stripped for nest lining. The exposed wood and fibrous remnants may bring to mind a buck rub, but buck rubs differ in several ways. Buck rubs are made on living stems that are more or less upright and have no obstructions that would hinder the approach of a large animal. Rubs are usually limited to one continuous section of the stem and occur at heights between 1 1/2 and 4 feet off the ground. Branches stripped by squirrels have random angles from vertical and could be anywhere from ground level (including fallen branches lying on the ground) to much higher. Bark is usually removed from multiple areas, and there may be a tangle of branches that would make it hard for a deer to reach the debarked sections. And finally, the wood surface of a buck rub shows signs of abrasion, while the wood exposed by squirrel stripping is mostly smooth.
Stripped branches do sometimes have telltale squirrel tooth marks like the ones in the photo below.
If you keep track of weather you’ll notice that cold nights are often followed by new bark stripping. I sometimes imagine a shivering squirrel thinking, “Wow, it was cold last night, I’m going to get more insulation for my nest!” Well, maybe it doesn’t happen exactly like that–sorry about the anthropomorphizing. But it’s clear that squirrels respond to cold with increased harvesting of fibrous bark. And it’s okay to imagine a squirrel sleeping in a cozy, insulated nest in a hollow tree on a cold winter night.
Rodents are the most common mammals on earth, in both number of individuals and number of species. They are also the most diverse, with lifestyles that range from semiaquatic through fossorial (adapted for digging and living mostly underground), terrestrial, arboreal, and even semi-aerial (gliding flight). But don’t let that mind-boggling profusion intimidate you. In our region many of the most common rodents are members of the squirrel family, a group that is remarkably uniform in physical features. Fortunately for the tracker this uniformity extends to track details and track patterns, and familiarity with the key features will aid in the recognition of any member of the group.
In the photo below you see tracks made by a gray squirrel bounding toward the top of the photo. The five-toed rear tracks lie in the upper part of the image, and the four-toed front tracks can be seen in the lower part. Claw marks show as tiny pricks ahead of the toes of both front and rear tracks. Notice that the toe pads of the three middle toes of each hind print are lined up close together, while the inner and outer toes lie farther back and angle to the sides. Behind the toes you can see a C-shaped grouping of middle pads. The front tracks have only four toes, but again the central two point more forward while the outer and inner ones point to the sides. C-shaped arrays of middle pads sit behind the toes of the front prints, and heel pads (there are two on each foot, but it’s hard to tell in this image) are situated behind the middle pads.
Bounding is the most common gait for most members of the squirrel family, and the resulting pattern is another recognizable trait of the group. In the photo above the two rear prints are almost even with each other and are set wider and well ahead of the front ones, which are also nearly even with each other. This positioning may seem odd, but there’s a logical explanation. At each bound the animal lands on its front feet and draws its rear feet forward so they pass outside of its front legs. As the front feet lift off the rear feet touch down–ahead of the spots the front feet just left–and propel the next leap.
The next photo shows a bounding pattern made by a red squirrel, again travelling from bottom to top. There’s a striking similarity to the first image of the gray squirrel tracks, in both overall arrangement and track details. Because the substrate was softer the rear feet of the red squirrel (in the upper part of the frame) sank in deeper–notice that the whole length of each of the three middle toes registered as a narrow groove. Nevertheless the three toes are closer together and oriented more forward than the outer toes, just as they were in the gray squirrel tracks. In the front tracks of the red squirrel (in the lower part of the photo below) the claws show as grooves rather than pricks, but the overall structure is similar to the front tracks in the preceding shot. If you look at the red squirrel’s right front print (at the lower right in the photo below) you can see clear impressions of the two heel pads.
The chipmunk tracks in the next photo (again bounding toward the top) are consistent with the features we saw in the red and gray squirrel prints. In the right rear print (in the upper right quadrant) you can see that the middle toes are closely grouped and the inner and outer toes are angled to the sides. The left front track (in the lower section a little below and to the left of the right front track) shows the four clawed toes, the C-shaped grouping of middle pads, and the two heel pads.
Mud is great, but winter is also fine for seeing squirrel family connections. In the photo below of red squirrel tracks in snow (bounding toward the top, of course) you see the same characteristic features you saw in the mud tracks. As sometimes happens, the heel area of the right rear foot (at the upper right of the photo) registered as a flattened area behind the middle pads. (If you look back at the first photo of the gray squirrel prints you’ll notice that the heel area of the left rear foot also made a slight impression.) There’s a variation in the arrangement of the front tracks, with the right front well behind but the left front farther forward. This kind of foot placement is often seen in squirrels, but is less common than the more four-square pattern.
Flying squirrels possess gliding membranes (the patagium) which extend between the front and rear legs, and because of this the rear feet can’t pass as far ahead of the front feet as they do in red or gray squirrels. In the next photo you see a bounding pattern made by a southern flying squirrel (oriented toward the top) in which the front prints are situated between rather than behind the rear prints. In northern flying squirrel trails the front prints often lie ahead of the rear ones. Another special flying squirrel trait is the thick covering of fur on the undersides of the feet. Because of this flying squirrel prints rarely show the crisp detail found in the tracks of other members of the squirrel family. But even with these differences, flying squirrel tracks will remind you of the tracks of other squirrels.
In the next image you see a bounding pattern made by a woodchuck. If you didn’t realize that woodchucks belong to the squirrel family, the familiar features of their tracks should make that clear. Woodchucks are more likely to walk than bound, and when a woodchuck does bound it usually places its front feet in a staggered pattern rather than even with each other, as in the photo. Nevertheless, the overall arrangement and the track details are consistent with those of its relatives.
To complete the picture for small rodents in the Northeast we need to add a few creatures that don’t strictly belong in the squirrel family but leave distinctly squirrel-like prints. These include white-footed mice, meadow voles, and their allies. I include mouse and vole allies because each one represents a group of closely related species which are difficult to distinguish from tracks alone.
First, let’s look at tracks of the white-footed mouse, shown below in a bounding pattern heading toward the upper right. In spite of its smaller size, the animal made tracks that are uncannily similar to the tracks in the first three photos. If I didn’t tell you that an individual rear print is just half an inch across you’d be hard pressed to tell these tracks from squirrel tracks.
Vole tracks also show striking similarities to the tracks we’ve already discussed–but with a few important differences. In the next photo you see tracks made by a meadow vole bounding from bottom to top. The track sequence, starting at the bottom, is: right rear, right front, left rear, left front. This staggered arrangement is common in vole trails and differs from the more consistent four-square bounding patterns usually seen in white-footed mice and tree squirrels. Voles can leave more regular bounding patterns, but they often move at something between a bound and a lope and their track patterns tend to be more variable. The toe impressions in vole tracks also tend to be more finger-like than the toes of mice. In spite of these differences the tracks of voles will remind you of mouse and squirrel tracks.
This is all well and good, you may say, but if these creatures are so similar to each other, how can I tell them apart? I’ve mentioned a few variations that can be helpful, but often the most useful trait is size. There’s a neat size progression, and although there’s some overlap between adjacent species it’s usually possible to make an identification with a few measurements combined with other clues. There are two dimensions to consider: track width (more reliable than track length) and bounding trail width (measured perpendicular to the direction of travel across the widest part of a bounding pattern). I’ll focus on the big picture rather than giving an exhaustive account of the numbers–detailed measurements can be found in any good tracking guide. White-footed mice and the smaller voles (woodland voles, for example) are the tiniest of the lot, and meadow voles are slightly larger. Chipmunks come next, and southern flying squirrels are slightly larger than chipmunks. Northern flying squirrels outweigh their southern kin, and red squirrels are larger yet. Gray squirrels beat out red squirrels, and woodchucks complete the series. These differences in body size are reflected in differences in track and trail dimensions, so a few measurements are usually sufficient to clinch an ID. Even when the tracks you’re dealing with are in the overlap zone there are usually other clues that can point toward an identification. And when all else fails, it’s okay to say you just can’t be certain. If you treat each situation as a learning experience, you’ll find yourself stumped less and less often.
Some animal communication is just for the moment, gone as soon as it is created, and some is more permanent. Whether it’s a patch of earth pawed by a deer, a scat deposit carefully positioned by a fox, or a twist of grass left by an otter, messages left in physical media can convey information long after the author has left the area. Squirrels are especially adept at this type of messaging, and their medium of choice is something they are intimately acquainted with–wood. Tree trunks, branches, roots–all can serve as bulletin boards for intra-species communication. One of the best times to observe squirrel marks is early spring, after the snow is gone but before new leaves limit our view through the forest.
The photo below shows an opening into the trunk of a large red maple. Hollow trees provide critical winter shelter, and this one must have been prime real estate because the hole has been bitten around the edges by a squirrel. Gray, red, and flying squirrels (of both sexes) use their incisors to declare ownership of desirable nesting spaces. Theoretically the sizes of the gouges should tell us which species did the marking, but the hole was about thirty feet up, and it’s hard to measure tiny things like tooth marks when you’re that far away.
The creature claiming possession of the tree in the next photo is easier to determine. Gray squirrels, primarily males, make vertical marks called stripes to assert territorial claims. They seem to prefer rough-barked trees like the white oak pictured in the photo, and the stripes are generally found on large trunks between 2 and 6 feet above the ground. I’ve also seen gray squirrel stripes on red oaks, chestnut oaks, hickories, and tulip trees. After marking, a squirrel may rub its cheek on the bitten area to leave its scent. You can see from the varying degrees of weathering that this tree has been marked repeatedly over several years.
Red squirrels also have distinctive ways of creating messages, and one of the easiest to find is the branch marking associated with conifer middens. Middens are accumulations of discarded cone scales and cores found below habitual feeding perches. The photo below shows a midden at the base of a Norway spruce. Most conifers, with the exception of some pines, tend to retain lower branches for years after they have died, and these provide perfect feeding perches. The oversized cones (up to 8 inches long) produced by Norway spruces are prized by red squirrels, and the middens came become quite large.
If you examine the branches above a midden you’ll probably find bite marks like the ones shown in the next photo. The image shows a Norway spruce branch which extends horizontally about four feet up the trunk. The upper surface of the branch is adorned by numerous bite marks. You can see the midden (out of focus) on the ground below the branch.
Red squirrels also make marks at or near ground level. In the photo below you see a Norway spruce root which has crossed over and been lifted over the years by the swelling root crown of a neighboring tree. This tree was part of a plantation that dated from the 1960s, and the trees were close enough together that horizontally spreading roots often passed close to the bases of neighboring trees. This also happens in other conifers when they grow in crowded stands, and the small lateral roots have thinner bark than the trunk and the larger roots.
A closer look, shown in the next photo, shows that a red squirrel has bitten through the bark of the lateral root. The light colored gouges are recent marks and the whitish ones are older, probably made the previous year and covered with dried resin.
Norway spruce plantations were established throughout the east during the Depression and also later in the 20th century. With their large crops of oversized cones, stands of Norway spruce are preferred habitats for red squirrels and are great places to investigate red squirrel marking. Other conifers were also used for reforestation projects, and if they support resident red squirrels you’ll probably find evidence in the form of marking and middens. Both branch marking and root marking are the animals’ way of defending their underground larders of winter food.
Squirrels also use their incisors for purposes other than marking, such as debarking trees to get at the living cells of the cambium. The photo below shows a staghorn sumac that was fed on by a gray squirrel. I found this a few years ago in early March, and the color of the exposed wood indicated that it had been done not long before. Late winter and early spring can be a time of scarcity; stored food supplies may be exhausted and squirrels may be forced to turn to foods which are less nutritious or harder to access. I’ve occasionally found similar cambium feeding by squirrels on sugar maples.
Squirrels, both red and gray, also tap trees when the sap flows in spring. The animals choose vigorous trees, and bites are made in living, thin-barked branches by anchoring the upper incisors and drawing up the lower ones. This creates what Sue Morse calls a d0t-dash pattern. Two fresh bites on a sugar maple branch are shown below, and above them there’s an older bite. Interestingly, the sap is not consumed immediately, but is allowed to dry. Once the water has evaporated the squirrel returns to lick up the crystallized sugar.
When we find a mark made by a squirrel, we can infer something about the availability of food or the presence of a desirable nesting site, but for other squirrels there’s much more involved. The associated cheek rub or saliva deposit is unique to the individual and carries information about its sex, health status, and possibly other characteristics. Even though receiving these messages is beyond our abilities, I enjoy finding squirrel marks and imagining the messages they convey to their neighbors.
Have you ever wondered what happens to all the bones? Animals are dying all the time, and when they die their soft tissues are eaten by predators and scavengers, picked off by birds, ingested by insects, and decomposed by microorganisms. This leaves just bones, like those of a rabbit shown below. But we don’t see bones littering the landscape, so what happens to them?
First let’s consider small animals. When a tiny creature such as a vole is killed by a predator, the catch is swallowed whole and the bones are crushed and partly assimilated. Undigested bone fragments are eliminated in scat (or pellets if the hunter was a hawk or owl). You can see small bone fragments in the red fox scat shown below–there’s also plant material, tiny hairs, and what appears to be a whisker. Scat like this will eventually be weathered and dispersed into the soil. Even if a small animal isn’t completely consumed immediately, its remains will be broken down, dispersed, and probably hidden from our view by its surroundings.
But what of larger animals whose carcasses would be more obvious? Deer immediately come to mind, but the question also applies to bears, coyotes, woodchucks, raccoons, and other similar sized animals. We do occasionally see the remains of recently deceased animals, like the deer carcass in the next photo, but why don’t we see piles of old bones lying around everywhere?
The answer has to do with the nutritional value of bones. The deer femur in the next photo was cracked open by a coyote to get at the marrow. (I say coyote because the only other animal in our region which is powerful enough to break a deer leg bone would be a bear, and there were no bears in the area where the bone was found.) Toward the upper end of the larger piece you can see some striations which were probably made by the coyote’s molars as it worked at the bone.
We sometimes see evidence of the utilization of bones this way in scat. The coyote scat in the next image contains an abundance of deer bone fragments and deer hair. The hair would have cushioned the sharp bone edges and prevented injury to the animal’s digestive system. It wouldn’t take long for bone fragments like these to be hidden in the upper layers of soil.
In addition to marrow, bones contain calcium, phosphorus, and other minerals which may be lacking in the diets of wild animals. Mineral deficiencies are especially likely for herbivores. Many animals supplement their nutrient intake by chewing on bones, and they usually choose less daunting ones such as scapulas, ribs, and vertebrae. The bones of birds, reptiles, and smaller mammals such as rabbits can also be utilized by less powerful animals. Even deer have been observed chewing on bones. This kind of chewing may not leave obvious signs–just ragged edges, missing ends, or random gouges.
Rodents also gnaw on bones, and the evidence of their activity is often more conspicuous. In the next photo you see a segment of deer leg bone lodged on a midden at the base of a Norway spruce tree. Middens, piles of discarded cone cores and scales, are created when a red squirrel repeatedly uses a favorite perch to feed on cones. The red squirrel that claimed this tree must have used the same perch to work on the bone.
In the next photo you can see the grooves made by a squirrel’s incisors as it chiseled off bone shavings.
Smaller rodents, like voles and white-footed mice, leave finer grooves like the ones in the next photo.
These creatures weren’t after marrow, since the bones were relatively old and the marrow had been removed long ago. This behavior is probably driven in part by the need to supplement their mineral intake, but rodents also chew on bones (and antlers as well) to maintain their teeth in good condition. Their incisors grow constantly, and are subject to malocclusion if not shaped and worn down with regular gnawing. The same is true for rabbits and hares, which are also known to gnaw on bones.
As time passes carcasses are pulled apart and bones are cleaned of soft tissue, scattered, broken, crushed, pulverized, chewed, and ingested by many different animals. Rather than piling up as useless cast-offs, animal bones gradually disappear as they are utilized by living creatures. Animals are part of the web of life both while they are alive and after they are dead.
The staccato warning call of a red squirrel is a common sound in our northeastern forests. These feisty animals are extremely protective of their territories, and they seem to react to the presence of people as much as to other squirrels. Red squirrels are found in both hardwood and coniferous woodlands, but their numbers are highest where there are extensive stands of conifers. In the Northeast one of their favorites is the Norway spruce (Picea abies). These majestic trees are native to northern Europe, but were planted extensively during the 19th and 20th centuries. Their tolerance of poor soils made them ideal for degraded sites, and many stands were established on abandoned farm land during the Depression.
Open grown Norway spruce trees are impressive for their height and form. The specimen shown above exhibits the large cones (up to 6 inches long) and the drooping branchlets that help to differentiate Norway spruce from other spruce species. In plantations the huge cones littering the ground reveal the tree’s identity, and even fairly young trees show drooping branchlets like those in the next photo.
Red squirrels feed on the cones of many different conifers, but they find the large fruits of the Norway spruce especially attractive. Cones are stored in underground larders and supply the animals with sustenance over the winter and often well into spring. Red squirrels like to feed on perches, and in winter they favor low branches located above or near their larders. Years of use can result in impressive middens of discarded cone scales and cores like the one below.
Conifer cones reach maturity in late summer, and the period between the exhaustion of the previous year’s provisions and the ripening of the new crop can be a lean time. Tree buds, berries, underground tubers, and insects help to carry red squirrels over this stretch, but conifer cones are their go-to choice. For most conifers species the cones don’t provide much nutrition until they have reached nearly full size, but Norway spruce is different. Because of their size, even immature cones attract hungry red squirrels. I’ve found evidence of red squirrels extracting tiny seed meats from the current year’s cones as early as late June. At this stage logs and stumps are often used as feeding perches. The red squirrel that left the remains in the next photo found a perfect picnic table.
In the close-up below you see the partly processed cone and some of the cone scales and seed remnants. Squirrels work on cones starting at the base, tearing off each scale and biting a hole in each seed coat to extract the nutritious contents.
Sometimes the accumulations of cast-off cone scales and seed remnants can be quite colorful. In the photo below there’s a pile of cone scales in the upper left and a scattering of winged seeds in the center. At the very top of the frame you see the outer aspect of several scales. Their exposed tips are bright green and the parts that were overlapped by the scales below are tan or reddish. Below and to the left of those, there are several scales with their inner sides showing. The green ovals outlined with red show where the seed wings were positioned. In the center of the photo you see what remains of the seeds, tan seed coats attached to the maroon seed wings. Ragged openings in the seed coats show where the meat was extracted.
The next two photos show the inner aspect of a single cone scale. In the first shot there’s one winged seed on the left, still lodged where it formed. The squirrel extracted the meat by biting into the base of the seed without displacing it. For the next shot I removed the seed so you can see how it rested against the inside of the scale.
As red squirrels begin to feed more and more on the current season’s cone crop, brightly colored discards pile up on the brown remains from previous years.
In a month or so red squirrels will begin the serious business of putting up stores of cones for the coming winter (see my post, Bounty From Above, September 14, 2020). If you do some investigating when you come across stands of Norway spruce you’ll get a look into the lives of red squirrels and the seasonal cycles which have shaped their behaviors.
It’s sugaring season, and the sweet bounty of spring is flowing. In sugarbushes all over the Northeast people are busy collecting the sap of sugar maples and processing it into maple syrup and other maple products. But we aren’t the only ones harvesting tree sap. Squirrels are also busy tapping trees, and the sugary nourishment makes an important addition to their spring diet.
You’ll find squirrel taps like the ones in the photo below on thin-barked branches or small trees. Black birch–pictured in the photo–and sugar maple are the most commonly tapped trees in the northeast, but they’re not the only ones. Sap containing sugars and other nutrients flows in all trees in late winter and spring when conditions are right. Sue Morse has documented squirrel taps on 23 different tree species.
To make a tap a squirrel turns its head sideways and uses its incisors to bite into the bark deep enough to penetrate the outer layers of sapwood. Sometimes, as in the photo below of a squirrel tap on a sugar maple, the resulting gouges make a dot-dash pattern. The dot is the spot where the upper incisors were anchored, and the dash is the cut made by the lower incisors as they were drawn toward the upper ones.
Both red and gray squirrels (and possibly also flying squirrels) make sap taps. Red and gray squirrels have been observed moving around in trees making numerous bites in rapid succession. But instead of licking the sap immediately they use a more efficient method, waiting until the water has evaporated and then returning to consume the crystallized maple sugar.
The squirrel tap on black birch in the next photo may have started as a simple dot-dash pattern, but it didn’t stay that way. It looks like the squirrel kept biting at it to make an irregular wound. The green surfaces are the cambium, the thin layer of living cells that produce wood and bark during the growing season. Just beneath the cambium is the wood formed in the previous summer. Its xylem cells are no longer alive, but they are connected end-to-end to form long tubes, and this is where most of the sap flow is located. Depending on the conditions, sap may also flow in the phloem cells of the most recently formed bark, located just outside the cambium. Once exposed, cambium tissue rapidly dies and turns brown, so I must have come upon this tap very soon after it was made. In the lower part of the photo you can see some dark brown bites that were made earlier in the same season.
Stems that are heavily tapped can take on a ragged appearance, as in the next photo of taps on black birch.
Once the growing season begins the tree attempts to heal the wounds. Cambium cells proliferate around the edges of the bared wood, and new callus tissue grows inwards. Small cuts may be covered in the first summer, but larger scrapes take longer. Tapping over several years can result in trees and branches covered with numerous callused scars, like those in the photo below of black birch.
So how does one find squirrel taps? Vigorous trees with plenty of exposure to the sun are preferred by the furry harvesters because they produce sap with high concentrations of sugars. Since most taps on large trees are too high for us to see from the ground, we’re limited to small trees or larger ones that have suitably low branches. But even if we find a big, healthy sugar maple with low branches it may not have any taps, because squirrels are choosey about the trees they tap. Individual trees may taste different because their chemical profiles aren’t exactly the same. Fortunately, wounds created by squirrel taps persist for months or even years, so if you locate a promising tree you may find evidence of sweet-toothed squirrels long after sugaring season is over.
Rodents are considered one of the most successful groups of mammals, so it’s not surprising that the northeast hosts many different kinds. They range in size from the tiny woodland vole (weighing an ounce or less) to the beaver (50 pounds or more). The small ones dominate, both in abundance and in their potential to confuse. Most of these little creatures are active in winter, so it’s a perfect time to get a handle on their distinguishing features.
The photo below shows a set of prints made by a red squirrel bounding from left to right. The five-toed rear tracks are nearly even with each other and set widely, their three middle toes parallel and their inner and outer toes diverging. The four-toed front tracks are set more narrowly and staggered, and their four toes are slightly splayed. Behind the toe impressions, the middle pads of both front and rear feet (analogous to the bumps over the knuckle joints in your palm and the ball of your foot) appear as clear indentations. The heel pads of the front tracks (like the heel of your hand) show in both right and left front prints, and the heel area of the right rear track (analogous to the heel of your foot) is a smooth elongation behind the middle pads.
Here’s a chipmunk group of four, with the direction of travel this time toward the top. The left front and rear tracks are partly superimposed, but the similarity to the tracks in the first photo is plain to see. This is what I call the rodent foot plan, and once you absorb it you’ll recognize it in other small rodents, including squirrels, chipmunks, mice, and voles.
But there are some variations which–if available–can be important in pinpointing an identification. The photo below came from the bounding trail of a southern flying squirrel, an animal similar to a chipmunk in body size (although lighter in weight). Compare the middle pads in the right rear tracks (the farthest to the right in each photo): in the chipmunk they’re well separated and form a sharp curve. The middle pads of the flying squirrel are closer together and form a gentle crescent.
If your reaction to that is, ‘you’ve got to be kidding!’ you’re not far off base. It’s a real difference, but snow conditions are rarely perfect enough to see that kind of detail. So how often can we be sure which small rodent made the tracks we’re seeing? Quite often, it turns out, because we have two additional diagnostic tools: trail width and habitual movement patterns. The tracks in the photo below, a white-footed mouse bounding toward the upper right and a gray squirrel bounding toward the lower right, are similar arrangements but are vastly different in size. In this case it’s easy to know which is which, but for less obvious differences, such as red squirrel versus gray squirrel, measurement of the overall width of the pattern, known as the trail width, can really help.
To measure the trail width of a bounding animal, imagine or mark lines parallel to the direction of travel which touch the outermost parts of the two rear tracks. Below you’ll see the same photo with lines delimiting the trail widths. Next, measure the distance between the two lines. The nice thing about this is that the trail widths of our most common small rodents fall into a simple size progression. In inches, trail widths for white-footed and deer mice measure 1 1/4-1 3/4; chipmunks, 1/1/2-2 3/4; red squirrels, 3-4 1/2; and gray squirrels, 4-6. At 1 3/4-3 inches the trail width for southern flying squirrels is similar to that of chipmunks, and northern flying squirrels, at 2 3/4-4 1/4 inches, overlap on the low side with red squirrels. Although trail width can be determined for any gait, the bounding gait so common in small rodents is especially suited to this measurement.
Habitual movement patterns are another useful tool for identifying small rodents. In the next photo a gray squirrel bounded at a good clip from bottom to top, leaving groups of four prints separated by relatively long distances. In each group of four the landing tracks of the smaller front feet are behind the take-off tracks of the larger rear feet. Bounding trails of red squirrels and chipmunks are similar in overall proportions. It’s not that these animals always make long leaps. If they’re moving slowly the distances between the groups of four can be smaller, and the hind feet may not pass as far ahead of the front feet. Compare the arrangement of the gray squirrel prints in the previous photo with that of the slower moving red squirrel in the opening illustration. The point is that the habitual travelling movement of these animals creates trails with characteristic four-track groupings and relatively large spaces between groups.
Compare the pattern above to the next photo, the trail of a southern flying squirrel, bounding from lower right to upper left. In this trail the larger rear prints are behind the smaller front ones, and the distance between the groups of four is smaller. In the trails of northern flying squirrels the rear tracks are often ahead of the front, but both species of flying squirrels have sacrificed strength for lightness and aerodynamic design and are unable to match the long leaps of their non-gliding relatives.
Snow depth can affect the foot placement of bounding rodents. To the white-footed mouse that made the tracks in the photo below the snow was fairly deep, so the groups of four are reduced to sets of two, each of the paired impressions made by sequential impacts of front and rear feet from the same side. All of the rodents I’ve been discussing do this when deep snow makes it more energy efficient. But even in these reduced patterns trail width can still be measured, as long as we make sure we’re looking at the actual tracks and not the larger openings around them. And like squirrels and chipmunks, mice make shorter leaps when moving less energetically. An example of mouse trails with consistently shorter leaps can be seen in the opening photo of last month’s article.
Meadow voles are chunkier and have shorter legs than white-footed mice, so they can’t make long leaps, but their trails are roughly as wide as those of mice. It’s not always easy to tell whether a bounding trail with short leaps was made by a vole or a mouse, but if the trail goes on long enough differences usually show up. A vole’s foot placement is rarely as even and foursquare as that of a mouse, and voles tend to make frequent shifts in gaits. It’s not unusual for an individual vole trail to vary among lopes, bounds, trots, overstep walks, and scurrying gaits that are difficult to categorize. In the next photo there’s a partly roofed vole tunnel meandering between the lower right and the top center. A vole traveled from the left side of the frame toward the tunnel in a bounding gait, with typical short leaps and uneven foot placement. The thin line in the center of the trail was made by the tail.
If you’ve made it this far in this treatise, you may feel like your brain is reeling. Believe it or not, I had to leave out many details, and I haven’t even addressed the issue of distinguishing small rodents from other small mammals. The important thing is to get started. Every time you work through a small rodent puzzle you’ll learn more. So be patient and persistent, and enjoy the eureka! moments when a few puzzle pieces fit together to form part of the larger picture.
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.
Image from TheSpruce.com
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.
