Beavers Posting Their Land
It’s not as neat nor as tall a mound as it typically is, but the vegetation you see on the bank of this pond is a beaver’s way of posting its territory. In two to three months, around the time that beavers give birth, the two-year-old beavers inhabiting a lodge typically leave to seek greener pastures in the form of unclaimed ponds or to form their own pond. No-one is quite sure whether parents encourage this departure, or whether the young beavers take it upon themselves to leave, but especially when the food supply is limited, the two-year-olds disperse.
Older, established beavers, having experienced this exodus themselves when they were young, are well aware that two-year-olds will be scouting for a new spot to set up residence in the spring. In order to discourage any potential intruders, beavers build one or more “scent mounds” on the shore of their pond or stream that consist of mud and vegetation they’ve gathered from the bottom of the pond or stream. They then walk over these mounds and excrete liquid castoreum from castor glands (located near their anal glands) onto it. The scent of castoreum is very distinctive and conveys information to beavers passing by that tells them that this location has been claimed and to move on. (If you come upon a scent mound, I encourage you to smell it – castoreum has, to some people, a very pleasing scent.)
Interestingly, castoreum contains salicylic acid, which is the active ingredient in aspirin. Salicylic acid is found in willows (which beavers eat), and native Americans used willow bark to treat headaches.
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Beavers Repairing and Reinforcing Lodges and Dams
Late October and early November is the busiest time of year for beavers. Their entire winter’s food supply must be cut, gathered, transported and piled next to their lodge so that they will have access to it under the ice. Mud, sticks, wads of grass and stones are collected to reinforce the lodge’s thick walls against the cold as well as coyotes and other predators. And dams, the structures which create ponds, must be patched and strengthened to withstand the rigors of winter.
The importance of maintaining a dam in good condition cannot be overstated, for without it, the pond would cease to exist, and no pond means no beavers. As Dietland Muller-Schwarze and Lixing Sun state in the Beaver, a beaver pond is a “highway, canal, escape route, hiding place, vegetable garden, food storage facility, refrigerator/freezer, water storage tank, bathtub, swimming pool and water toilet.” (They defecate only in water.)
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Beavers Grooming
Beavers spend an inordinate amount of time grooming themselves (and each other). Both inside their lodge and on land a beaver tucks its tail between its legs, sits up on its hind legs and spends up to an hour at a time fastidiously combing through its fur often multiple times a day.
Both front and hind feet are pressed into service. The two inner toes on each hind foot are modified for grooming – the second toe has a “split nail” with a nail and a horny growth between the nail and the toe which has a finely serrated upper edge that serves as a fine-toothed comb.
Grooming serves two purposes. One is to remove debris from the coat, from algae to burrs and parasites. The other is to waterproof the beaver’s coat. A beaver applies an oily substance from its anal glands to the outer layer of hair with the help of its toes, thereby preventing its inner, denser, underfur from getting wet.
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Beaver Scat Anomaly
Finding an animal’s scat is usually pretty straight forward. The shape, size and contents (in this case egg-shaped, one-inch pellets of wood fibers resembling sawdust) of scat tells you who likely deposited it. But the location and amount of this beaver’s scat is highly unusual.
This pile was discovered on a road that passes between two large bodies of water. While beavers are commonplace here, finding their scat on dry land is an anomaly. Beavers are known to defecate only in water.
Often you will find beaver scat where they have been working, such as in the water right below a dam, but usually there are only a handful of pellets, if that —nowhere near the amount in this photograph. One can only wonder what might have caused this unusual deposit. (Photo by Jody Crosby)
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Great Blue Heron Ingenuity
I had to laugh this morning about what I witnessed just after posting about male Great Blue Herons collecting and delivering sticks for their nest. It occurred to me that I have seen hundreds of sticks being brought to nests, but I have never actually seen a heron in the act of collecting a stick. Lo and behold, today was my lucky day. At least one heron came up with an extremely efficient and energy-saving strategy for accomplishing this task.
Being largely fish eaters, herons typically raise their young in wetlands where food is plentiful. Many of these wetlands are created by beavers, who set up housekeeping there as well. Herons owe not only their habitat to beavers, but also, in this case, their nesting material. A veritable goldmine of sticks is right underneath the heron nests, free for the taking right in the middle of the heron rookery in the form of a beaver lodge. Fortunately for the beavers, there is a limit to the size of the stick a heron can carry.
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Spring Has Sprung!
March is the absolute high point in anyone’s life who anticipates and celebrates the annual celebration of the arrival of spring. For this reason, it is the first chapter in my book “Naturally Curious” – every day brings confirmation that no matter what is going on in the human world, you can depend on the natural world to observe the rites of spring.
Mourning Cloak butterflies emerge from behind loose bark, migrating American Woodcock probe the mud, sleepy Eastern Chipmunks appear above ground, Red-winged Blackbirds return, Beavers see the sun for the first time in perhaps months, buds swell with newly accessible sap, Red Fox kits emerge from dens, Wild Turkeys mate, Spring Peepers peep, Painted Turtles emerge from hibernation and bask in the sun, Ruffed Grouse drum and Skunk Cabbage blooms.
For at least a few minutes a day, we can lose ourselves in the natural rhythm of life that surrounds us.
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Beavers & Pounding Headaches
Beavers will do their very best to secure fresh cambium as long as they have access to land. Even when thin ice starts to form, they are undeterred. You can hear them as they use the top of their heads to bump up against the ice in order to break through and create a pathway to shore. Thanks to Kay Shumway, a beloved friend, I had ten good years of observing this behavior every late fall/early winter. Eventually the thickness of the ice confined the beavers to their lodge and the surrounding water beneath the ice, but until that happened you could count on seeing the sun glinting off the ice shards that inevitably ended up on top of the beavers’ heads.
Beavers Actively Winterizing Lodges
There are two noticeable differences in the appearance of an active beaver lodge in the fall as opposed to the summer. One is the presence of a growing pile of freshly-cut branches adjacent to the lodge. These branches provide resident beavers with the nutrition they will need during the winter months when herbaceous plants are neither available nor accessible.
The second change noticeable in a fall lodge is the presence of massive amounts of mud. Branches are often placed on top of this layer of mud, so you have to observe the lodge before that happens in order to see the extent of the mud layer. It provides protection from harsh winter winds which would significantly lower the temperature inside the lodge. Together, a blanket of snow and a layer of mud serve as excellent insulation for beavers living in the lodge.
In the Northeast, where the temperature often dips into the single digits or lower in the winter, the interior of an active beaver lodge maintains a relatively stable 33° F. – 35° F., roughly the temperature of the water, thanks to the ingenuity of these rodent architects.
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The Surprisingly Varied Diet of Beavers
It is common knowledge that beavers are herbivorous but the extent of their herbivory is not always appreciated. Examining their skull would tell you that their massive four front incisors (as well as the muscles attached to their jaws) are designed to do some serious chewing. And serious chewing does take place, especially in the fall. Poplars, birches, alders, willows, maples and many other deciduous trees as well as a few conifers are felled in order to reach and consume the inner bark, or cambium layer. (The de-barked logs and branches are subsequently used to repair dams and lodges). Not only do Beavers need to meet their daily nutritional needs but they must cut enough trees to last them through the winter.
However as spring approaches and they can access land, their diet changes from the woody branches they’ve been eating all winter (from their winter food pile under the water) to a diet that consists mainly of herbaceous plants. Ninety percent of their time is spent eating non-woody plants, often skunk cabbage, water lily rhizomes and grasses in the early spring. As summer progresses, they seek out aquatic plants, ferns, sedges and a variety of flowering plants. Usually it’s not until late summer/early fall that their incisors are once again given a good workout.
The pictured Beaver had the good fortune of having a large patch of tasty Jewelweed (Impatiens capensis) growing on and adjacent to its lodge.
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Wood Ducks Returning To Northern New England
A welcome sign of spring in northern New England is the return of the Wood Duck to wooded swamps and wetlands. There are seven species of North American ducks that regularly nest in cavities and the Wood Duck is uniquely adapted for doing so. Its slim body allows it to use Pileated Woodpecker cavities for nesting and the acuity of its large eyes allows it to avoid branches while flying through wooded areas. Even so, it still tends to make one look twice to see ducks perched up in a tree!
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Beavers Released
Most beavers in northern New England have been trapped inside their lodge for several months, with their only food supply being the branches they cut last fall and piled up on the floor of the pond or river near their lodge. Ice has sealed them in, not only to a life of darkness and dampness, but to a diet of cambium.
Needless to say, they are quick to take advantage of melting ice that allows them to exit their lodge and make their way to shore to sample fresh food. One of the first delicacies they dine on, if it’s available, is skunk cabbage. The rhizomes, leaves and flowers of both yellow and white pond lilies are also favorites. No longer restricted to woody plants, beavers head for grasses, sedges, ferns, fungi, berries, mushrooms, duckweed and even algae as the water warms. Their palate must jump for joy with the melting of ice in early March.
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North American River Otters Use Abandoned Beaver Lodges As Dens
North American River Otters use dens (called holts) for giving birth and for shelter from weather extremes. Den sites are usually close to the water line of rivers and lakes, and have multiple entrances underwater as well as on dry land. They are often excavated under trees or rocks or in river banks, but otters also use abandoned muskrat burrows and beaver lodges as shelters (cohabitation with beavers has also been documented – see https://naturallycuriouswithmaryholland.wordpress.com/2013/02/22/beaver-otter-cohabitation/).
One of the most obvious and distinctive signs of otter occupancy of a den is the presence of their scat in the vicinity. It usually has little form; rather, it consists of loose piles primarily composed of fish scales. Pictured is an abandoned beaver lodge that is currently occupied by several otters whose scat in the foreground and tracks and slides in the vicinity confirm their presence. A lack of any beaver sign indicates the lodge has been abandoned by its original inhabitants.
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Muskrats Foraging
Usually at this time of year, Muskrats are restricted to foraging beneath the ice and eating their mostly herbivorous diet inside “push-ups” — huts made out of excavated vegetation that have been hollowed out and serve as protective outposts where they can eat and rest. Because of warmer weather this winter, many ponds have retained open areas where Muskrats (and Beavers) can climb out of the water and enjoy sunshine (if they’re lucky) and fresh air while they eat.
Unlike Beavers, which store their winter food in a pile adjacent to their lodges in the fall, Muskrats forage for food on a daily basis throughout the winter. While occasionally they eat small fish, clams, snails and turtles, Muskrats’ preferred diet is the roots, stems, leaves, and fruits of many water plants, such as cattail, water lilies, and rushes. Equipped with a thick, waterproof coat of hair, they are capable of remaining submerged up to 15 minutes collecting food due to a decreased heart rate and oxygen stored in their muscles.
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What Determines The Internal Air Temperature Of An Active Beaver Lodge In Winter?
Regardless of the outside temperature, the interior of occupied beaver lodges has a fairly stable temperature of about 32°F. This is due to several factors, one of which is insulation. Beavers spend much of the fall collecting and stuffing mud into the cracks between the branches that provide a framework for their lodge (leaving a mud-free air vent at the top of the lodge). This mud as well as any snowfall that occurs during the winter help keep out the cold and retain the warmth that the resident beavers’ bodies radiate.
A comparison of the (cooler) interior temperature of bank dens and that of open-water lodges confirms that the temperature of the substrate underlying a lodge also contributes to the air temperature of the chamber.
Lastly, heat produced by beavers raises the temperature of a lodge above that derived from the lodge substrate.
(Photo: beaver lodge on a morning cold enough to show “beaver breath” escaping through the air vent that runs up through the center of the lodge to its peak. Thanks to Kay Shumway for photo op.)
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Beavers Gathering & Caching Winter Food Supply
Beavers are busy reinforcing their lodges and repairing dams as the days shorten and temperatures fall. Once these tasks are taken care of, they begin gathering and storing all of the food that they will need this winter, for once ice forms they will no longer have access to land.
Their winter food cache is placed as close to the entrance of their lodge as possible, as the inhabitants of the lodge will be swimming out to this pile frequently to obtain food. After hauling branches and saplings to the lodge, the beaver dives down and jabs the butt end of the branch into the mud at the bottom of the pond. Additional branches are woven into this base layer until eventually most caches weigh two or more tons. One can often see the pile’s top branches and leaves rising above the surface of the water.
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Unusual Beaver Activity
Beavers are known for their ever-growing incisors which allow them to cut trees down, eat the cambium (a nutritious layer just beneath the bark) and cut what’s left into pieces they are able to haul and use as building material for dams and lodges. More often than not, it’s straight forward work.
Occasionally not every step is taken – you can find standing trees that had the bottom three or four feet (as high as the Beaver could reach) of cambium removed without the trees being felled. You can find de-barked logs that have been left where they fell and not carried or floated to the dam or lodge as construction material. It’s also not unusual to find standing trees where several times a Beaver has attempted but failed to cut all the way through.
Recently John Twomey brought to my attention a tree felled by Beavers unlike any other I’ve ever seen: one or more Beavers had cut down a Paper Birch and eaten the cambium layer, leaving the tree clean of bark. At some point they cut into the tree every 18 inches or so, not quite severing the pieces, but leaving them connected by a core of wood that ran the length of the tree. If any readers have seen anything similar to this, or if you have an idea as to why Beavers would have cut the tree in this fashion, Naturally Curious would love to hear from you. (Photo by Prentice Grassi of his sons investigating said tree earlier this spring.)
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Beavers Foraging
Even in the coldest of winters, there is often a thaw around this time of year that frequently allows beavers to escape the cold (+/- 34°F) dark lodge where they reside during most of the winter. Our most recent thaw was such that in many beaver ponds, ice didn’t even have to be broken in order for resident beavers to forage for food on land.
When beavers are confined to complete darkness (under the ice) their 24-hour circadian cycle extends to a 28 hour day. During this time beavers sleep for longer periods at a time and thus need less food. As spring approaches and the days lengthen, the slightest exposure to daylight will reset the beaver’s biological clock back to the circadian cycle. (Leonard Lee Rue, Beavers) (Photo by Alice Trageser)
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Beavers Feeding Young
In summer Beavers spend considerable time on land searching for, cutting and bringing vegetation back to their young in the lodge. Their woody plant preference (they eat large amounts of herbaceous plants during the warmer months, but also some trees) tends towards the inner bark (cambium) of willow, aspen, maple, birch, cottonwood, beech, poplar, and alder trees. This beaver, however, has retrieved a Red Oak sapling for its offspring.
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Muskrats & Spatterdock
Cattails, sedges, rushes, water lilies and grasses make up the bulk of a Muskrat’s diet although these aquatic rodents have been known to occasionally dine on fish, crustaceans and freshwater clams.
Muskrats typically don’t eat their food where they find it – they usually bring it out to a feeding platform in the water, which provides them with some protection from predators. However, they make an exception for Bullhead Pond-lily flower buds (Nuphar variegata), also known as Spatterdock, which they often devour on the spot wherever they find them (see photo). Beavers, Porcupines (yes, Porcupines can swim), White-tailed Deer and waterfowl also dine on the leaves, rhizomes, buds, flowers and seeds of Bullhead Pond-lilies.
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What Goes On When We’re Not Looking
A blind is a wondrous thing, allowing you to observe natural behavior in a natural setting. Having watched beavers for over 50 years, I thought I had seen most of what there is to see regarding Beaver behavior, but this particular morning I was witness to a new activity, namely a game of tag.
The resident Beaver spent the better part of half an hour chasing ducks around its pond. A pair of Mallards were subjected to this annoyance first. When approached, the Mallards would swim away together, with the drake quacking loudly, but obviously weren’t put out too much by this game as they tolerated it for about ten minutes before taking off (undoubtedly in search of a more serene body of water).
No sooner had the Mallards left than a pair of Hooded Mergansers arrived. The Beaver greeted the newcomers and proceeded to chase them around and around the pond, occasionally catching up to them, and then restarting the game all over again. Eventually the mergansers, too, departed, leaving the Beaver king/queen of his/her castle. (Thanks to Mike Keating for photo op.)
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Canada Geese Nesting On Beaver Lodges
If you are fortunate enough to have a beaver pond near you, you should give the lodge more than a cursory glance this time of year. It is common to find Canada Geese nesting on beaver lodges, for obvious reasons – safety from most land predators. While Common ravens have been known to raid Canada Goose nests for eggs and goslings, the overall rate of survival of the goslings of lodge-nesting geese is very high.
A Canadian study showed that ponds with beaver lodges (and therefore Beaver activity which warms the water and thaws the ice) thaw at least 11 days sooner than ponds without Beavers, allowing early access to water for Canada Geese returning for the spring nesting season. Battles between pairs of geese vying for these coveted nesting sites are not uncommon.
Canada Geese have much to thank Beavers for. Not only can geese get an early nesting start on beaver lodges, they have a relatively safe spot to incubate their eggs and raise their young.
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Muskrats Cohabit With Beavers
Muskrats, or “rats,” as they’re sometimes derogatorily called, are semi-aquatic, mostly plant-eating rodents that live in ponds, streams, lakes and marshes. During the winter they seek shelter in lodges that they build out of grasses, reeds, cattails and sticks. Muskrat lodges are much smaller than Beaver lodges, which are constructed out of mud and sizable branches, sticks, stones and mud.
In the spring Muskrats often build nests by burrowing into a stream or pond bank, which they enter under water. Muskrats are also known to set up residence in active Beaver lodges. After dining on aquatic vegetation, the pictured Muskrat made a beeline for the beaver-occupied lodge nearby, and dove under as it approached it. Beavers and Muskrats tolerate each other’s presence in the same pond (and lodge) even though they both consume much of the same vegetation. Unlike Beavers, Muskrats supplement their diet of plants with frogs, crayfish, clams, snails, and fish. It may be that when cohabiting a lodge, they may help one another keep an eye out for predators. (Photo: Muskrat eating pond vegetation)
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Beavers Seeking Green Food
Although spring is arriving a bit later than usual this year, there are beaver ponds where the ice has started to melt and resident beavers have wasted no time in exiting the water. (Where ice is thinning, they are known to bump their heads up against it in order to break through.)
Having had a diet of bark all winter (from the underwater supply of branches they stored last fall), beavers head for a greener diet if it can be found. Skunk cabbage, where it’s present, is the first fresh food of the season for beavers. The rhizomes (underwater stems) of water lilies, as well as the leaves and flowers when they appear, are also favorite foods. As spring advances into summer, grasses ferns, sedges, and all manner of herbaceous flowering plants are eaten.
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Beavers Breeding
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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