Signs of Winter 8: A Walk at Harrison Hills Park

Photo by D. Sillman

It was a cold, clear, sunny afternoon at the end of the first week of January. Deborah and I had the day to ourselves and decided to go for a short walk up at Harrison Hills Park. We had heard that a beaver had been spotted in the park’s big pond and wanted to see if we could get some pictures.

We got to the parking area about 1 pm and headed off down the pond trail. There was a dusting of snow lingering in the shady places along the trail and under it the ground was frozen solid. In places where the sun (which was brilliantly glaring in a bright blue sky!) hit the trail, though, the snow and soil had melted into a slippery layer of mud. It was about 34 degrees air temperature but the sun felt warm on our faces.

We walked through the black cherry dominated woods and eased past the spot where bluebells will be blooming gloriously in the early spring. We walked past the small meadow where one of our bluebird boxes was set (a box that did not have any nests or fledges last year but seemed so perfectly placed for bluebirds that we left it in place for next spring and summer. Maybe the bluebirds will come to their senses and use it this coming season!). There were woodpeckers (mostly downies) pounding on the trees along the trail and a hint of larger noises (pileated woodpeckers?) further in the distance.

Photo by D. Sillman

As we headed down the west facing slope to the pond, there was a constant rustling in the thick shrubs of the surrounding understory. The glare of the sun made it difficult to see colors, but the sizes of the birds shuttling from branch to branch around us made us think of robins. Finally we heard familiar robin chortles and calls and got some back-sightings of their red breasts and black bodies. The woods were full of robins!

We soon realized why the flock was here. Most of the understory was made up of berry bearing shrubs and vines. Barberry and spice bush and honeysuckle were interlaced with bittersweet vines and they all were covered with mostly red (but also clusters of black) fruit. Further, this hillside was a great solar collector especially in the afternoon as the weak winter sun dropped into the western sky. We could feel the air temperature go up several degrees as we walked along. Added to the food and warmth there was also a dense stand of spruce trees at the top of the hill that would provide sheltered night roosts for the birds. There must have been hundreds of robins twirling about in the dense shrub layer.

We always think of robins as migratory “signs of spring,” but they will stay in Western Pennsylvania through the winter if there is sufficient food. Holly thickets are great places to find overwintering robins, as are some city neighborhoods and also sheltered berry thickets like this. It is interesting that most of the plants making this habitat so ideal for the robins are exotic invasive species. Oriental bittersweet, Japanese barberry and Tartarian honeysuckle are the major berry producers here. Each has merited a “noxious weed” designation and has caused extensive native species declines, but here, collectively, they are making life so much easier for the robins!

Photo by D. Sillman

We got down to the pond and walked as quietly as we could in hopes of seeing the beaver. The small island in the middle of the pond had a pile of freshly cut sticks stacked up on it. The pond water had thin skim of ice on it and, as the sun began to ease down below the forested rise to the west, a shadow slowly crawled across it. You could feel the air temperature falling as the sun drew down. It was going to be another very cold night!

The beaver did not pop up out of his den. We did not get a picture of him. Clusters

Photo by D. Sillman

of alders next to the pond’s edges, though, had been gnawed through and it was obvious that the sticks piled up on the island were mostly from these freshly cut trees. Most of the gathered sticks were about two inches in diameter and about four or five feet long. They would not only provide some shelter for the beaver but also food, as the inner bark of alder is a rich carbohydrate source (and a favorite food for beavers). We didn’t see any foot prints in the soft mud around the pond but did see piles of gnaw-chips.

Beavers instinctively build dams from the small trees and branches that they cut with their powerful front incisors and carry and float and then mud-cement into place along small streams. These dams create protective ponds within which they can build their lodges. This beaver, though, sidestepped all of that instinctive building behavior by selecting an already constructed pond. Lodge construction, though, which will be the eventual outcome of all of those piled up sticks (if the county doesn’t come and trap out the beaver!), seems to be a learned behavior. Lodges set in the middle of a protective pond may have a variety of geometries 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). It will be interesting to see (again, if the county doesn’t intercede) what school of architecture this beaver ascribes to!

Beavers are obligatorily vegetarians. They 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.

We stayed around the pond for about an hour. The beaver never showed himself, but the evidence of his activity was everywhere. There was very little alder still standing around the pond. He would have to shift over to some other type of wood if he wanted to continue to add to his lodge or needed to accumulate more food. Poplars and aspens are other highly preferred food trees, but these are not abundant around the pond. Beavers also eat maples (especially red maple), birches, cottonwoods, willows and even pines. I am sure that he would find sufficient forage within a short waddle of the protective pond.