Friday, January 11, 2013

Beaver Facts

Our latest beaver adventures in beaver trapping led me to review their chapter in Mammals of Missouri by Charles and Elizabeth Schwartz.  This is a tremendous resource, compiling more mammal details than any other single source.  The Missouri Department of Conservation web site has good general information but doesn't have space for all the little incidentals that Schwartz lists.

Underfur, guard hairs and front claws
The beaver hide is covered with dense soft underfur for warmth.  Reddish to black longer guard hair on the outside protects the underfur from environmental factors and trauma, keeping the animal fluffed, dry and warm.  Slipping my fingers into the underfur, it felt soft and almost dry, providing excellent insulation.  The front feet are equipped with long claws, allowing it to dig its den into the creek bank. The beavers' large hind feet are specialized for swimming with webbed toes.  The webs also help it walk across soft muddy ground.  

Webbed hind foot
Click to enlarge

Beaver have especially large lungs which hold a supply of air as well as an enlarged liver which stores enough oxygenated blood to permit beavers to stay underwater for 15 minutes at a time.  They can thus swim long distances under water and into safety, avoiding predators.

Double-edged secondary claw
The hind toes of a beaver have special grooming adaptations.  The three outer toes of the hind feet have typical claws, but the two inner toes possess specialized claws that are used to comb the fur, remove parasites, and distribute oil. "The innermost toe has a long, double-edged claw that clamps down over a long, soft lobe, forming a 'coarse comb'; The second toe has a similar claw but possesses a horny growth with a sharp finely cut upper edge between the claw and the soft lobe below, forming a "fine comb."*

Beaver in southern Missouri seldom construct lodges and tend to live in bank burrows.  The fast flowing, flood prone streams tend to wash out the dams frequently, making the mounded homes they build up north more temporary.  Here we identify their location by food piles of sticks stored under water as well as their slides and harvested stumps.  Their burrows along Bull Creek are frequently limited by the rocky shelf under the soil.  They will raise the roof close to the top soil, causing a collapse.  This may cause them to create a new burrow as well as promoting further bank erosion with the next flood.

In the 1860s there were still lots of beaver in all the Missouri watersheds in spite of commercial trapping.  By 1895 there were only a few left due to landscape changes and uncontrolled trapping with improved techniques.  From 1928 to 1955 there was a restocking program, importing beaver from other states.  As far as Bull Creek is concerned, this has been a tail-whopping success! 

* Quotes from The Wild Mammals of Missouri by Charles and Elizabeth Schwartz, University of Missouri Press. 2001.


  1. Hi there, I am very surprised to read that your beavers in Missouri seldom construct lodges. The same can not be said about beavers up here in Ontario. You will find beaver lodges around just about every bend in a river. Over the past year my wife Jean and I, have filmed and followed the life of beavers in different parts of Ontario. We have posted some of our pictures, along with some HD video, and stories at:

  2. I enjoyed seeing your pictures. This is more like the Canada waters I remember. The valleys are wider and flatter as are your shield lakes. Your beaver are a valuable keystone species, creating habitat for fish and moose alike.

    The Ozarks is a high plain, dissected by streams flowing for many thousands of years. Our Southern Missouri streams tend to be narrow, rock or gravel bottomed and coursing through the deep valleys The water coming off the sides produces the rapidly flowing streams which created created these valleys.

    In a normal year, there will be 2-4 heavy rains capable of washing out any dam or lodge. In 16 years, I have seen only one attempt at lodge building, which was washed away after 4 months. I suspect that, like Liz Taylor's many marriages, it was a temporary triumph of evolutionary habit over experience.