Signs of Winter 7: Beavers and Otters

Photo by Steve, Wikimedia Commons

Over the past few weeks I have had two very interesting communications from friends and colleagues here in Western Pennsylvania. One involved signs of beaver activity along the Kiski River and the other involved seeing river otters in one of the ponds at Harrison Hills Park.

The beaver report was from Carl Meyerhuber who, up until this extreme cold spell anyway, has been braving the winter weather each afternoon to do his two mile walk on the Roaring Run Trail along the north bank of the Kiski River. Carl has been seeing gnawed tree trunks and piles of chisel-shaped wood chips at spots along the trail, sure signs that the Kiski beavers are out and about.

Beavers (Castor candenesis) were once a very common component of the fauna of not only Western Pennsylvania but almost all of North America. These large, semi-aquatic rodents once had a continental population of sixty to ninety million individuals. They were, however, of great economic value to Europeans moving across the continent (and some say they were one of the main reasons that the Europeans moved across North America as quickly as they did!). By the end of the Nineteenth Century, there were only a fraction of the original continental population still alive, and there were no beavers at all remaining in Pennsylvania.

Conservation programs were established in Pennsylvania to try to re-establish beaver populations. In 1917 a pair of beavers from Wisconsin was released in the state, and between 1918 and 1925 one hundred more were brought in and released into our waterways. By 1934 the beaver populations had grown sufficiently that a regulated trapping season was established.

Photo by Hugo.arg, Wikimedia Commons

Beavers instinctively build dams with the small trees and branches that they cut with their powerful front incisors. They carry and float these building materials to constricted points along small streams and then mud-cement into place across the water flow. These dams create protective ponds within which the beavers can build their lodges. Lodge construction, though, seems to be a learned behavior. The “island-type” lodges set in the middle of a protective pond may have a variety of geometries

Photo by R. Stevens, cynic.org.uk

and styles but all have a number of underwater entrances and exits and at least two inner chambers (one for drying off after returning from a swim, and the other for sleeping and rearing their young).

Beavers may also build their lodges onto and into the banks of larger rivers. These “bank beavers” are the same species as the island-lodge beavers but adapt themselves to a landscape in which flat, slow flowing streams suitable for damming are not available. These river bank lodges are also constructed of mud-cemented sticks and logs, and they also have multiple below water entrances and exits and at least two internal chambers. These lodges may also extend into the soil of the river bank often in and around protective and supportive roots of large river bank trees. Both types of lodges become extremely secure in the winter as the mud holding the sticks and logs together freeze into a nearly impenetrable, concrete-like mass.

The beavers along the Kiski are “bank beavers.” The steep hillsides coming down to the river do not provide sufficiently flat expanses for beaver dams to generate protective ponds. When you drift down the Kiski in a canoe (an activity that should wait for MUCH warmer weather!) you can see these beaver lodges tucked into river bank. If you happen to be out near sunset, you may even glimpse one of the beavers as they start into their nocturnal foraging for building supplies and food.

Beavers preferentially eat water plants when they are available but survive on the inner bark of a variety of trees especially through the winter. They cache large quantities of sticks and branches under their lodges for winter consumption when conditions do not allow them to forage freely about. Poplars and aspens are preferred tree species but maples (especially red maple), birches, willows, cottonwoods, and pines are also consumed. The increased cutting activity that Carl has observed along the Roaring Run Trail is probably due to a stimulated gathering of winter food by our local beavers.

Public Domain, Wikimedia Commons

There are lots of neat details about beavers! Their front incisors continuously grow! These tree-cutting teeth are harder in the front than they are in the back and, so, wear into a beveled biting instrument that generates the very recognizably shaped wood chips around any beaver tree site. Beavers are the second largest rodent on Earth (exceeded in size only by the capybara of South America). Ten thousand years ago, though, an ancestor species of our North American beaver was the size of a black bear and weighed close

to five hundred pounds!

Photo by D. Azovitsev, Wikimedia Commons

The other semi-aquatic mammal story of the moment was actually mentioned (and pictured!) in the local newspaper a couple of weeks ago. Two river otters (Lutra canadensis) were spotted in one of the ponds up in Harrison Hills Park in northern Allegheny County.

Like the beaver, river otters were once abundant and widely distributed in Pennsylvania. But, also like the beaver, human impacts (through direct hunting and also through indirect destruction of the otters’ habitats through land clearing and stream pollution) greatly reduced the Pennsylvania otter population and functionally extirpated the river otter from almost all of the state’s waterways. In 1982 researchers from the Game Commission and Frostburg University released one hundred and fifty three wild otters that had been captured in Louisiana, Maryland, and New York into nine rivers in Central and Western Pennsylvania. In the intervening thirty-three years these otters have multiplied and spread throughout the watersheds of Pennsylvania.

The otters released into the Allegheny River (one of the nine original release sites) were undoubtedly the stock from which the Harrison Hills otters were derived. It is a very long climb up from the Allegheny to the bluffs on which Harrison Hills park sits, but the promise of fish-rich pond waters must be quite an attraction for these active predators.

In 2006 Deborah and I and Marian and Joe were canoeing on the Youghiogheny River (another release site for the otters) when we spotted an otter swimming and playing among the river rocks. She seemed as interested in us as we were in her, and the few minutes we spent observing each other was the highlight of that glorious river trip.

Beavers, otters, wild turkeys and bald eagles are all symbolic of Pennsylvania ecosystems steadily regaining some of the charismatic fauna that they have lost over centuries of ignorance and misuse. These animals make even simple walks in the woods and quiet floats down a stream potentially so much more exciting and so much more filled with adventure!