Some animals live among us almost undetected, and others leave evidence that is obvious and long-lasting. Beavers are a good example of the latter, leaving signs of feeding on woody plants and creating dams and lodges that may last for years. The featured photo shows a lodge made of mud and sticks and surrounded by protective moat of water. What we can’t see is the underwater entrance which leads upward to a dry, multi-level living area. In the upper left quadrant of the photo there’s a dam, seen from the upstream side. The freshly peeled sticks that decorate the lodge and the dam, and the water lapping right up to the top of the dam, indicate that there were beavers in residence when the photo was taken.
Beaver dams can be impressive structures. The next photo is a view of a dam from the downstream side. The heaped up sticks conceal inner layers of mud interlaced with more sticks. Beavers react to the sound of flowing water, and any leaks are plugged with mud and more sticks. As long as the dam is maintained, the water level stays high enough to keep the lodge (not seen in this photo) secure in its watery surroundings.
A little exploration around the edges of an active beaver colony will turn up additional signs. When whole trees are removed the only thing left may be a chewed stump like the one below. Wood chips scattered nearby show where branches were removed and the trunk was sectioned and dragged off.
Some logs may remain where they fell, but they seldom go unused. One such log is shown in the next photo, and it’s a nice demonstration of the beaver’s chewing technique. The horizontal row of small cuts along the edge of the bark shows where the upper incisors were anchored. The vertical grooves in the lower peeled part of the log were made as the lower incisors were drawn up toward the anchored upper incisors. And why all this chewing? To get at the living cambium cells, located between the wood and the outer bark. Although there are exceptional cases where other food is available (such as the rhizomes of water lilies), most beavers depend on the cambium of woody plants for survival when leafy vegetation isn’t available.
Many dams and lodges are used for several years in succession, and newly added sticks and branches stand out against the mud and older sticks. The residents of a beaver colony also create deliberate messages indicating their claim to the location. In the photo below you see mud that was dredged up from the bottom and deposited on top of a grass hummock to create a scent mound. Whatever is handy at the edge of the pond, whether it be mud, muck, or rotting vegetation, can be dredged up and carried to the shore to make a pile. The final touch comes when the beaver drags its anus over the mound and deposits urine and secretions from its anal glands and castor sacs. The smell is not unpleasant, but it’s hard to describe. It reminds me of a horse barn, but it has also been compared to musk, human sweat, cheese, fruit, leather, birch beer, or some combination thereof. Scent mounds are most often created in spring, and the distinctive odor can persist for weeks.
If ponds and small streams aren’t available, beavers take up residence in creeks and rivers. But these habitats are subject to regular flooding, and the volume of flow during high water would destroy dams and lodges, so river beavers make their homes in the stream banks, digging underwater entrances and excavating living spaces above water level. If beavers are living in a river you may find peeled sticks, cut stumps, and scent mounds along the riparian margin. Another good clue is tracks in silty or muddy stream margins.
The tracks in the photo below were made by a beaver walking from lower right to upper left. The large hind prints make a wide zig-zag, starting with the left rear in the lower right corner. As in other four-footed walking trails, there are two footfalls–a front and a rear from the same side–at each zig or zag, but the front prints are mostly covered by the larger rear prints. All, that is, except for the two tracks at the upper left. The larger print above is the right rear, and next to it, just below, is the much smaller right front. Some of the rear prints may remind you of the tracks of a large bird. That’s because beavers often touch down lightly or not at all with their two inside toes, so the outer three toes make the most prominent impressions. But the heel marks behind the toes (as well as the wide palm areas at the bases of the toes) tell us it was a beaver, not a bird.
Whether they’re pond beavers or river beavers, at some point the animals will have exhausted the local food supply and will be forced to relocate to a better situation. If dams and lodges are not maintained water levels will fall. Chewed stumps and peeled sticks will weather to dull gray. Even though they aren’t fresh, these signs will persist and provide clues to the past presence of beavers.
But an abandoned beaver pond can offer its own discoveries. The amount of material amassed to form a dam or a lodge can only be appreciated after the water is drained. The exposed mud can be a great place to find the tracks of other creatures. And old beaver ponds provide great opportunities to find beaver scat. The animals normally defecate in the water, so seeing fresh scat is rare. But once the water has drained out, scats may be left on the sloping inner sides of the dam and the perimeter of the pond. Beaver scat is oblong and can be anywhere from 1/2 to 1 1/4 inches in length. The fibrous content is easy to see in the photo below–a beaver needs to chew through lots of bark and wood to get enough nutrition.
I never get tired of visiting beaver sites, because there’s always something new to discover. Whether it’s the prodigious size of a felled tree, the clever way the animals engineer channels to make transporting logs easier, or a muddy stream margin decorated with the tracks of beavers commuting to and from work, it’s always fascinating. Beavers lead complex lives and show great ingenuity in dealing with their surroundings, and the signs they leave can give us a window into their cleverness and adaptability.