Friday, October 30, 2015

New Beaver Lodge

A beaver moved into the storm water pond below my home in the aftermath of the horrific June 2013 Calgary flood. A longstanding beaver lodge on the Elbow River about a kilometer away was damaged and perhaps rendered uninhabitable by the flood surge. I know the adults from this lodged survived because I saw them searching for their kits in the days immediately after the flood. They were out during the middle of the day, which is unusual, and they were combing the shoreline in a search-like behavior. Sadly, the kits I saw earlier in the year were likely lost in the deluge. I suspect the beaver that relocated was from this lodge.

In the two falls and springs since the flood, the lodge has slowly increased in size and the number of Aspens around the pond have dwindled. The ground around the pond is littered with felled trees, and debarked and debranched trunks. Beavers are herbivores and prefer Aspen and Willow species. They eat the bark and the smaller branches.

The photo above shows a submerged grove of relocated Aspen branches in the water in front of the lodge. After debranching a trunk, the beaver tows the branches on the surface of the water to the lodge and then anchors (plants) the cut ends into the mud at the bottom of the pond. The branches in the photo are an "all-season, living, vegetable garden" for the beaver. The Aspen leaves were green until the autumn chill turned off the chlorophyll growth. The submerged branches will serve as the winter food source for the beaver. 

The photo above shows one of the dozens of Aspen cut down by the beaver within the last year. The protective wire mesh was not high enough to offer any impediment to the beaver. Beaver incisors are very sharp and their lower jaw muscles are powerful enough to cut through a tree this size in minutes. Beavers tip their head sideways at a 45 degree angle and make cuts until the upper and lower incisors meet and then they turn their head in the opposite direction and make opposing cuts on the other side. They move the head back and forth until the trunk is severed. The tree is felled to gain access to the branches and the bark of the trunk. 

The photo above shows the higher end of a felled trunk. The exposed bark has been eaten. Perhaps the beaver prefers the thinner, softer newer bark higher in the tree rather than the older, thicker bark at the bottom.

The photos below show close ups of the cutting marks from the beaver incisors. Beaver incisors are about a cm wide and the grooves confirm this.

I have only seen one beaver at a time in the pond and I am not sure if the lodge is home to a breeding pair. If so, perhaps next spring I will see new kits. With more beavers, the existing Aspen around the pond will likely all disappear within a few years. Fortunately Aspen grow quickly.

1. Naughton, Donna. The Natural History of Canadian Mammals. University of Toronto Press. 2012.

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