Beaver Biology

As many may know, Crossroads Pond has been the home to a resident beaver for the last year or so.  It has built a lodge on the side of the pond opposite to Creek Road, shown in the picture below.


I understand from Chris Mendel, Pennypack’s Executive Director, that a second beaver, presumably female, has joined him, and that there is the potential prospect for a litter of beaver kits in the spring.  On my walk on Wednesday 12/19 there were signs of fresh beaver activity around the pond.  I thought it might be time to learn more about beaver biology.

Pennypack Creek is home to a resident beaver population.  While beavers were nearly eradicated from North America by the fur trade, federal and state laws protecting them in the early 20th century have allowed for population recovery including in Pennsylvania.  We typically think of beavers building dams across small streams to form beaver ponds.  They then build their lodge in the pond.  However, in larger streams such as Pennypack Creek which are too big to dam, beavers may also build dens by burrowing into the bank of the stream.  The Crossroads Pond beavers are likely offspring of beavers who lived in such bank dens, but who found their way into the obviously appealing man-made pond in the Pennypack Preserve.  Beavers mate in winter, typically around January-February and deliver the litter of 3-6 kits about 4 months later.  Kits often remain with their parents in a colony for up to 2 years.  A beaver lodge may ultimately contain 2 or 3 generations of beavers.  Beavers are strict vegetarians and eat the leaves, buds, twigs, and inner bark of trees.  To access the branches, they girdle and ultimately topple trees.  They store branches under water near the lodge as a winter food source.  Branches are also used for building and repair of the lodge or dam.  While beavers prefer aspen and poplar, they will use a variety of tree species as availability dictates.

Evidence of beaver activity is plentiful around Crossroads Pond.  This tree (white ash I think) was cut a few months ago as evident from the weathering.



These three trees on the west side of the pond are in the process of being felled.  The center tree will probably come down with the next storm, while the other two are still in the process of being girdled.



[1/4/19 update.  The center tree above has come down as expected.  The trust has put wire cages around a number of mid size trees in the same area presumably to deter beaver activity.]

This small willow tree which grew on the little island in the pond (where the geese typically nest) has been cut since summer.



What will be the long term effects of beaver activity on Crossroads Pond?  In general, beavers are thought to have beneficial effects on forest ecosystems.  By damming streams and creating ponds, they increase the diversity of the ecosystem by creating new habitats with different plants than the surrounding forest which in turn attracts more diverse wildlife.  This may be a less relevant issue at Crossroads Pond, however, which is man-made and was present before the beavers arrived.  With the recent heavy rains, the pond is already overflowing onto the road, so it is unlikely beaver activity could raise the pond level further.  The physical appearance of the pond will inevitably be altered, particularly if the colony grows.  Beavers are unlikely to eradicate any species, but medium sized trees (like the ones shown above) will be cut and replaced with saplings from seeds from surrounding tree species.  Beavers are like humans in the sense that they must alter their habitat to survive.

The Pennypack Preserve continues to be a fascinating place to observe nature.  For several years we have been graced with the opportunity to observe bald eagles nesting.  For some, the ability to watch a beaver colony in action will be an equally exciting opportunity.  For others, there may be distress at the alteration of the woodland ecosystem around the pond.  If there is anything that is certain, it is that nature is always changing.

If you are interested in learning more about beavers, check out these websites:

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