Beavers are in the middle of their breeding season, which means copulation takes place under the ice, undetected by human eyes, making information about their reproductive habits hard to come by. What is known about the breeding practices of North America’s largest rodent is that beavers form permanent breeding pairs and are monogamous through consecutive breeding seasons. Should a beaver’s mate die, a new one will take its place. In a colony, only the adult (individuals which are at least three years old) pair breeds. Mating usually takes place in January or February, and typically occurs at night in the water. Gestation is roughly 128 days and three or four kits are born in May or July.
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This photograph conveys the essence of a beaver’s summer – eating and grooming… more eating, more grooming. During the summer months, beavers feed on non-woody vegetation (grasses, ferns, aquatic plants, etc.) 90% or more of the time. (During March/April and October/November, their diet switches to 60%-90% tree bark, and during the winter, bark from trees stored under water composes 100% of their diet.)
When beavers are not eating, much of their time during the warmer months is spent grooming, both themselves as well as each other. Combing debris out of their coat (with the help of a split nail on both hind feet) and applying oily material from their anal glands to waterproof their fur consume much of their waking hours, both at night as well as at both ends of the day. (Castoreum, produced in castor sacs, differs from anal gland secretion, and is used primarily to mark territory.) (Thanks to Roger and Eleanor Shepard, and Sara and Warren Demont for photo op.)
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Porcupines are forced to exert a lot of effort if they are in need of food and the snow is deep. Unlike many rodents that are light enough to travel on top of the snow, Porcupines must plow their way through it. Their weight, short legs, and bare footpads make traveling in snow challenging, to say the least.
If the snow is deep, the winter ranges of Porcupines are considerably smaller (18 acres in one research study) than their summer ranges (160 acres in same study). Because of the energy needed to travel through the snow, Porcupines usually feed just a short distance from their winter dens, more often than not within 200 feet. Their feeding trails from rocky or hollow tree dens to their woody food sources (often Eastern Hemlock-note bits of branches on snow in photo, American Beech and Sugar Maple), are very distinctive. They are used every night when Porcupines leave their dens to feed and again several hours later when they return. These trails become well marked with urine, and less frequently with scat and quills. (Photo insert: Porcupine rock den entrance)
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Microorganisms inside a deer’s four-chambered stomach enable cellulose in the plant material consumed to be digested. In winter, the microorganisms within the deer stomach are different from the microorganisms in spring, summer, and fall. This change allows deer to digest a diet of woody browse during winter months and turn the high-fiber diet into proteins through intricate physiological processes. Among their preferred browse are White Cedar, Yew, American Basswood, Alternate-leaved and Flowering Dogwood, Maples, Staghorn Sumac and Witch Hobble.
Offering food items during this period other than woody browse (such as hay) is detrimental to deer, as it requires different microorganisms in the stomach in order to be digested. Thus, even though a deer’s stomach might be full (of hay, for instance), it may starve due to the inability to digest it. (Photo: White-tailed Deer browsing on Eastern Hemlock)
We’re right on the verge of when beavers will no longer be able to smell fresh air, see the sun and obtain fresh bark. Until the temperature drops to around 16 degrees F. they continue to break through the thin ice covering their pond. Once the temperature remains in the teens or lower for several days, they no longer try to break through the ice and are sealed under it until spring, unless there’s a mid-winter thaw.
Once beavers are confined by the ice, their activities outside the lodge are minimal. Beavers leave their lodge in winter primarily for three reasons: 1) to swim out to their winter food supply pile and retrieve a branch which they bring back into the lodge to eat, 2) to defecate in the water, and 3) to mate in January or February. Other than these excursions, they spend most of their days in the dark, enduring life in a lodge that has a temperature of about 34 degrees F. (Thanks to Kay and Peter Shumway for photo op.)
By the end of August, White-tailed Deer fawns are about three months old. Their mother weans them between two and four months of age and during this time they molt, losing their white spots. A new gray-brown winter coat replaces the coat they were born with.
Muskrats are primarily herbivorous. The majority of their diet consists of the tubers, roots, stems, leaves and fruit of a variety of aquatic and terrestrial plants, particularly those of bulrush, cattail and arrowhead. A diet of high fiber is possible because of bacterial fermentation which takes place in their intestines. The digestion of many herbivores is aided by bacteria, but many plant-eaters are restricted in what they can eat because they are unable to change their diet without killing the bacteria. Muskrats, however, can and do consume large amounts of meat (frogs, fish, turtles, crayfish, etc.) and still maintain a healthy population of fiber-digesting bacteria. (Thanks to Jeannie Killam for photo op.)
Even if you didn’t know that a white-tailed deer’s diet changes in the fall, their scat would be a dead giveaway. Its texture and formation are excellent indicators of what a deer has been eating. During the summer, individual pellets are often lumped together due to the moisture content of their summer diet (grasses, clover, alfalfa, apples and other herbaceous food). As winter approaches, deer transition to a diet of twigs, leaves and acorns which results in the formation of individual, dry pellets. At this time of year, it is possible to find both forms of deer scat.
One associates Beavers with a fairly strict diet of bark and twigs. While their winter diet consists primarily of woody plants, they consume a variety of herbaceous and aquatic plants (as well as woody) during the spring, summer and fall months. Shrubs and trees make up roughly half the spring and autumn requirements, but as little as 10% of the summer diet when herbaceous plants such as sedges and aquatic plants become available.
Recent observation of a local active Beaver pond revealed that Interrupted Fern (Osmunda claytoniana), Jewelweed/Touch-Me-Not (Impatiens capensis) and grasses are high on the list of preferred foods of one Beaver family during the summer, although woody plants such as poplars (Populus spp.) and Paper Birch (Betula papyrifera) have also been consumed in fairly large quantities. All too soon Beavers in the Northeast will be limited to the bark of branches they’ve stored under the ice. Until this time, they take advantage of the accessibility of more easily digested herbaceous plants. (Thanks to the Shepards and Demonts for photo op.)
Being ruminants, white-tailed deer have a four-chambered stomach which allows them to digest a wide variety of food, including leaves, twigs, fruits and nuts, grass, corn, alfalfa, and even lichens and fungi. Their stomach hosts a complex set of microbes – organisms such as bacteria, which are too small to be seen with the naked eye – that change as the deer’s diet changes through the seasons.
In general, the green leaves of growing plants are consumed in the spring and summer, while fruits and seeds are eaten as they become available. Hard mast foods, such as hickory nuts and acorns, are an extremely important component of fall and early winter diets when deer need to establish fat reserves. The buds and twigs of woody plants are a mainstay of their diet in winter.
At this time of year it is not unusual to see deer grazing in fields that are just starting to have a touch of green. Grass is a welcome change from their winter woody diet, but it only comprises a very small (less than 8%) of a deer’s overall diet, due to its low crude protein and digestibility. Because their rumen (the stomach chamber where most microbial fermentation takes place) is small relative to their body size, a white-tailed deer’s diet must be high in nutritive value and capable of being rapidly degraded in the rumen. Therefore, white-tailed deer rely primarily on alfalfa, clover, beans and other legumes, additional herbaceous flowering plants, and browse, all of which have more protein and are more easily digested than grasses.
Alas, yesterday’s Mystery Photo ‘twas not made by a squirrel loaded down with a bag of nuts, a guess hazarded by one reader, but, as most of you knew, it was created by a Porcupine, or Quill Pig (Erethizon dorsatum). A bit pigeon-toed, Porcupines walk with their feet pointed slightly inward, with their feet flat on the ground. Their pebbly soles rarely leave a distinctive pattern, and their toe pads are not usually evident, but under the right conditions, their nails do make an impression. Usually a Porcupine’s quill-laden tail is raised slightly as it moves, but occasionally it drags along the surface of the snow as the Porcupine walks, producing a broad band composed of very fine lines that weaves between the Porcupine’s tracks, as in yesterday’s photo.
Moose are ruminants, as are cattle, goats, sheep and deer; they have a four-chambered stomach, which is necessary in order to digest the cellulose in the vegetation they consume. Food goes to the rumen and the reticulum, the first two chambers, which contain bacteria and other microorganisms that help digest the cellulose as it mixes with saliva. Here the food separates into solids and liquid material and the solids clump together to form the cud, which is regurgitated and chewed a second time in order to break it down into smaller bits. The third chamber, or omasum, functions as a pump, sending the food to the final chamber, the abomasum, where the digestion process is completed.
Yesterday’s design was made by a beaver as it removed bark from a tree. The light-colored, curved little “bumps” that run horizontally across the middle of the tree were made by the two incisors in the beaver’s upper jaw. When eating the sought-after cambium layer of a tree, beavers grip the tree with their two upper incisors as they scrape towards their upper jaw with their two bottom incisors, sometimes creating this pattern. (Individual marks where the upper incisors gripped the bark and the four incisors didn’t quite meet can be seen in the insert.)
The ever-growing incisors of rodents are harder on the front surface (outer layer is hard enamel, colored orange from iron in a beaver’s diet) than the back (softer dentine), so the back of each incisor wears away faster than the front, creating a sharp, chisel-like edge to these four specialized teeth. So functional are beavers incisors as cutting instruments, Native Americans used to insert a beaver incisor in a wooden handle and use it to cut bones and to shape their horn-tipped spears.
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Wherever there is scat, or dung, there are dung beetles. This is a photograph of a dung beetle in heaven as it has located a black bear’s gigantic (apple-filled) scat, which will provide it with food for a long, long time. Some species of dung beetles (rollers) shape pieces into balls and roll them away and bury them to eat later or lay their eggs on. Some species (tunnelers) bury their dung by tunneling underneath the pile of scat. And a third group (dwellers) actually lives inside dung piles.
Most dung beetles prefer the scat of herbivores. There are always bits of food that do not get digested, and these bits are what a dung beetle feeds on. Dung beetle larvae eat the solids, while adult beetles drink the liquids contained in the scat. A given species of dung beetle typically prefers the dung of a certain species or group of animals, and does not touch the dung of any other species.
Dung beetles have a brain that is the size of a grain of rice, yet they are very sophisticated insects. They use celestial clues (the Milky Way) in order to roll balls of dung in a straight line. Dung beetles are known for “dancing,” which helps them orient themselves after their path has been disrupted. They use their dung balls to regulate their temperature, and cool off. (In very warm climates, around noon, when the sun is at its peak, dung beetles will routinely climb atop their dung balls to give their feet a break from the hot ground. Thermal imaging has shown that dung balls are measurably cooler than the surrounding environment, probably because of their moisture content.) And dung beetles keep track of the number of steps they take and the direction from which they came (instead of landmarks) in order to return to their nest with a ball of dung.
Even though they are remarkably clever, dung beetles can be duped! A flowering plant native to South Africa (Ceratocaryum argenteum) produces large, round nuts that are strikingly similar in appearance, smell, and chemical composition to antelope droppings, which the dung beetles accordingly roll away and bury, effectively sowing a new generation of C. argenteum.
There are a few weeks in September and October when acorns (and beechnuts) are mature enough to eat, but haven’t yet fallen to the ground. Porcupines take advantage of this nutritious supply of food that is not yet accessible to small rodents, deer and turkeys, and climb oak trees to consume acorns. Because an average porcupine weighs between 12 and 35 pounds, it is unable to climb all the way out to the end of a branch, where acorns are located, so it nips off the tips of fruit-bearing branches and then scoops out the acorn, leaving the cap still attached to the branch (diagnostic porcupine sign). When all the acorns on a branch have been eaten, the branch is discarded. You can often find many of these branch tips, or “nip twigs,” in the canopy of large oaks on a good mast year, but inevitably some fall to the ground. The end of the twig is usually cut at a 45° angle, and often you can see the lines made by the porcupine’s incisors. (Beechnuts are also harvested in this manner, as are the cones and terminal buds of eastern hemlock in winter.) Red squirrels also nip twigs in order to reach fruit, but typically do so when they harvest the cones and terminal buds of conifers. (Thanks to Ethel & Michael Weinberger for photo opportunity)
For the most part, muskrats are herbivores. They consume with relish the leaves, stems and rhizomes of emergent aquatic plants such as cattails, bulrushes, sedges, horsetails, water lilies and arrowheads. Fish, frogs and invertebrates, including crayfish and clams, are also eaten to a lesser extent. Muskrats are voracious eaters (captive muskrats eat 25 – 30% of their weight daily). When their numbers are very high, muskrats can cause what is referred to as an “eat-out,” where they mow down everything in sight.
Like beavers, muskrats can close their upper lips behind their incisors in order to cut plants underwater without taking in water and choking. (photo: two young muskrats feeding on aquatic vegetation)
Bones, antlers, skulls, turtle shells – all are recycled relatively quickly by rodents seeking a source of minerals, particularly calcium and phosphorus. All rodents possess four incisors, two in the front of the upper jaw and two opposite these, on the bottom jaw. These incisors, unlike other teeth, never stop growing. By gnawing on hard objects such as bones, rodents keep their incisors paired down. If an incisor is broken or lost, the opposing incisor will continue growing in a circle, having nothing to grind against, causing the rodent to die of starvation or from having its brain pierced (through the roof of the rodent’s mouth) by the ever-growing incisor. In this photograph, a gray squirrel is obtaining minerals and sharpening its incisors on a moose skull that a human wedged into the crotch of a tree.
During the winter, white-tailed deer browse on the twigs, buds and bark of trees. Deer have incisors in the front of their bottom jaw, but none in the front of their top jaw, just a hard palate. They grip the bark with their bottom front incisors and scrape their jaw upwards, leaving behind grooves the width of their bottom incisors. Often there are frayed ends of bark at the top end of the groove, due to the deer having to use its hard palate and incisors, rather than two sets of incisors, to separate the bark from the tree. Favorite trees include red and striped maples, oaks, poplar, pines, hemlock, arborvitae and balsam fir.
Your guesses were outstanding – especially “Pinocchio scat” and “petrified baby hippopotamus”– and a couple of readers even nailed it: part of the intestines of a porcupine. (Many of you suggested it might be a black bear’s fecal plug – not a bad guess – though any bear that had to pass something this large when it woke up might decide to hibernate year round.)
Mystery Photo Explanation: A fisher killed and ate a porcupine, choosing not to eat (and leaving behind) a portion of the porcupine’s digestive tract called a cecum – a sac located between the large and small intestine where the cellulose in leaves and bark that a porcupine eats are broken down.
During the warmer seasons of the year, porcupines feed on sugar maple buds, leaves of basswood, aspen and beech saplings, grasses and other herbaceous plants, apples, acorns and beech nuts. In winter, their diet consists mostly of leaves (mainly eastern hemlock in the Northeast), which contain low levels of nutrients and high levels of dietary fiber. Certain mammals and birds possess specific bacteria that secrete enzymes capable of digesting the cellulose in fiber (beavers, hares, rabbits and ruffed grouse come to mind) through the process of fermentation. Because these enzymes work slowly, the digestive tract of a porcupine is very long (26% of a porcupine’s total weight) and the fiber passes through it slowly.
A majority of the bacterial activity in a porcupine’s digestive system takes place in the cecum, which is about the same size as a porcupine’s stomach. Here fermentation turns finely ground woody material into molecules small enough to be absorbed by the porcupine’s body. (A process referred to as “hind gut fermentation.”) Research shows that 16% of a porcupine’s energy requirements are supplied by the porcupine’s cecal fermentation.
Porcupines spend a lot of their life climbing on and clinging to trees due to their woody diet. In addition to strong, curved nails that fit into bark crevices, the soles of their feet have a pebbly surface with very little fur. The bumpy texture increases the surface area and the friction when a porcupine’s feet are in contact with a branch, helping the porcupine hold onto the tree trunk and branches. Even so, examination of porcupine skeletons confirms that many have fractures that have healed, indicating that a significant number of porcupines, while their bodies are adapted for climbing, still experience falls during their lifetime. (Photos: porcupine footpad; insert – porcupine footpad in fisher scat)
Some beavers are still managing to find openings in their ponds which give them access to fresh cambium, the soft layer of wood just under the bark of a tree. Cambium contains a lot of cellulose, in addition to starches and sugars. Like all herbivores, beavers do not possess enzymes that are capable of breaking down the large cellulose molecules (cellulases). In their place, beavers employ micro-organisms, such as bacteria, that can break down cellulose.
These bacteria are located in a pouch called a cecum, located at the beginning of the large intestine. (Ruminants such as moose and deer have rumens in place of ceca.) Colonies of these microorganisms in a beaver’s intestines digest up to 30% of the cellulose from the woody material that it eats. Further nutrients are recovered in the form of fecal pellets that the beaver re-ingests.
Beavers are constantly grooming and oiling their fur in order to keep it waterproof. To groom itself, a beaver usually sits upright with its tail between its back legs protruding in front of it, exposing the cloaca – a single opening for all the functions of the scent, reproductive and excretory organs. After the beaver climbs out of the water onto land, it often shakes its head and scrubs its ears and face. Then it thoroughly scrubs its shoulders and belly. The beaver gets oil from its inverted oil glands with its front feet, and then rubs it all over its body, using both front and hind feet. The second toe of each hind foot has a split nail (see insert) which the beaver uses to distribute the waterproofing oil and to comb debris out of its fur. Without this coating of oil on their fur, beavers would soon become water soaked and would not be able to tolerate the cold water.
In this photograph, perhaps for the last time outside of their lodge before their pond freezes, beavers engage in a practice known as “mutual grooming” during which they attend to each other’s coat using their teeth instead of their feet as combing utensils. (Photo: adult on left, offspring on right)
Woodchucks are one of the few species of mammals that enter into true hibernation. When the temperatures dip into the 40’s, usually in October or November in the Northeast, most woodchucks leave their summer burrows and head for the woods, where they dig a tunnel that ends in a chamber that is well below the frost line (and therefore above freezing). Here they curl up in a ball and live off of the 30% additional body weight they put on in the fall. In order to survive until March or April, a woodchuck’s metabolism slows way down. Its heartbeat goes from 100 beats a minute to five, and its body temperature goes from 96 degrees F. down to to 47 degrees F.
During the summer, porcupines are almost always found out in the open. At the end of October/beginning of November porcupines den up for the winter in the Northeast, with up to a dozen porcupines sharing the same den. While some adult males will spend days at a time in a conifer, most porcupines seek out rocky crevices in which to spend the day, with a smaller number finding shelter in hollow trees. Porcupines are hardy creatures – while dens do protect porcupines from heat loss, they contain no insulation, the entrances are open and the porcupines don’t huddle together for warmth. In addition, porcupines emerge from their dens to feed at night, when outside temperatures are lowest. (And yes, that is porcupine scat that is stuck in/on the porcupine’s quills.)