Native Animal of the Month: Beaver (Castor canadensis)

Written by Jennifer Callaghan
    Monday, 13 April 2015
Native Animal of the Month: Beaver (Castor canadensis)

I have a confession. A part of me enjoyed when the Riverside Park beaver was a secret. I liked sneaking through the park examining tree trunks along the river for signs of beaver chewing. I enjoyed watching the progress of the chew on the large cottonwood that first revealed signs of the beaver. I enjoyed sharing the location of the tree with nature-loving volunteers and I entertained myself by photographing two of those volunteers with the last name "Beaver" kneeling next to the tree pretending to gnaw at the bark.

I have been monitoring mammal populations in Riverside Park since 2006, and since that time, I have ever only known of a few signs of possible beaver activity in Riverside Park. In 2007, there were two separate reports (one highly credible) of a beaver seen swimming along the river by the Locust Street Bridge. Then sometime around 2009, a tree in the park was found with possible beaver chew, but the chew never grew in size and further activity was never documented. There were other miscellaneous reports of beavers swimming in the Milwaukee River over the years, but they always turned out to be muskrats that had been misidentified, and so it seemed Riverside Park was without a beaver population.

IMG 1014Notable reports of resident beavers not even a mile north of Riverside Park have been documented sometime between 2005 and 2014. The possibility of a pair of those beavers producing a kit that would mature and disperse down to Riverside Park was completely plausible, which is why the "buck-rub" I discovered on a cottonwood at the end of July last year caught my attention. It seemed too low to the ground to be from a deer, yet it was also difficult to differentiate from some random tree disease because the tree was really only missing a patch of outer bark. It appeared to have marks resembling teeth, but I assumed I was letting my imagination run wild. Yet, when I returned a couple weeks later it became evident that the missing bark was definitely the result of a hungry beaver. The patch (at right) had grown quite noticeably and displayed beautiful patterns where the formidable incisors had intricately carved the wood. Riverside Park definitely had a new beaver visitor!

But, was the beaver a new resident too? We monitored the chewing progress on the tree over several weeks and noticed a couple of other trees also starting to show signs of beaver chewing. When it became clear that the beaver was trying to take down the large cottonwood along the riverbank with the initial chew, we placed a field camera in an adjacent tree to try to photo-document the large rodent. Our first week-long attempt with the camera was unsuccessful and we worried that the beaver may have moved along. Yet several days later, fresh wood chips appeared again at the base of the tree, and so we re-erected the wildlife camera in the tree. Luck was on our side this time and 7 days later we had photographic evidence of Riverside's own Castor canadensis! The beaver was documented in many photos working solo late in the evening for hours at a time (below).

EK001051It took the beaver a little over 2 months to take down the large cottonwood about 50 meters north of the canoe launch. During that time he also took down a few smaller willows and ash trees on either side of the canoe launch. In late-fall he started working on the area by the outflow in Riverside Park and then a little further south on both sides of the river across from Wisconsin Paperboard. When conducting our 2014 Christmas Bird Count along both sides of the river in the greenway, we noticed the extent of the beaver's work in the area. We estimated he had gnawed down somewhere around 60 trees of various sizes all around the Greenway from Locust Street to North Avenue, proving he was completely worthy of his "busy beaver" moniker.

Due to his lack of a lodge and den, the young beaver was able to work inconspicuously for quite some time. But, our beaver could only remain anonymous for so long. One can only chew down so many trees in a public park before people start to notice. When the winter ice melted, the beaver diligently got back to task and his hard work revealed itself. Some called him a vandal, others called him a nuisance, and one - who knew his true identity - even called him a "large rat." And when the news crew showed up on-site, our culprit had no choice but to publicly reveal himself. The jig was up and the beaver claimed responsibility for the "vandalism" he had committed to so many trees in the area.

But, now that our little guy is known to the masses, we hope people will show him a little respect. We have no plans of eradicating our new resident because we're pretty excited about his presence. A beaver is a keystone species and his existence in the park means that habitat quality is pretty good. We've worked hard to improve habitat in Riverside Park and the trees felled by his chewing will provide habitat for a significant number of other species (invertebrates, decomposers, birds, etc.). Chewing deterrents can always be placed around trees if it becomes problematic, so for now, the beaver is free to move around on his own free will.

There are a noticeable number of new trees down in the Riverside Park area and the big question is whether our beaver friend is still working alone. We hope to put up field cameras in the area again this spring and photo-document any new activity. Because, who knows, maybe there is a Mrs. Canadensis too! And maybe I'll be lucky enough to stumble upon the couple's den tucked along the river bank under a large willow somewhere. Or maybe I'll find their litter of plump, furred kits romping along a clump of downed twigs. And I'll keep it a secret. At least for a moment. I'll savor that period in time before our friends were celebrities, and selfishly, I'll etch every detail in my brain. But, I promise to share it, because even though I relish the Beaver's pre-TMJ days, I've realized how fun it can be when other people share in a really cool secret. Now we can officially state that our long-toothed friend is our newest resident!

Stay tuned for Part 2 of The Native Animal of the Month: Beaver (Castor canadensis).

* Photo of beaver: purdue.org

Jennifer Callaghan

Jennifer Callaghan

Jennifer came to Wisconsin later in life, but has fully embraced the great state of Wisconsin as home. Her first career was as a professional ballet dancer, but a lifelong passion for nature and animals led her to a second career in environmental biology. She loves to learn new things and share her love of nature with others. In her free time she likes to travel and stay active with her awesome husband and sweet little dogs.


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