Friday, December 16, 2011

Beavers

I never tire of seeing signs of beaver. This clever and hard working large rodent is perfectly suited to its life in water and on land. Beaver are busiest at night, fixing their lodge, repairing the dam, making and marking scent mounds on shore, and gnawing down trees for construction projects and for food.

Several of my regular local haunts that I visit with Kodi lead past ponds or river oxbows occupied by beavers. At one such place this week I discovered a new lodge built among a fallen red maple tree near the shore of a river oxbow.




The lodge is built of sticks and packed with lots of mud. Beavers dive down to the bottom of the river or pond to dig up soft mud, clasping it to their chest as they swim back up to the lodge. The well-built lodge includes an inner chamber about 2 feet high and 6 feet or more wide, that is built above water level. It is big enough for the family - typically the parents, two to three young of the year, and two 1-year old offspring. Sometimes the 2-years old stick around, but usually they disperse in the spring to set-up their own territory upstream. The lodge has a vent in the top to allow air exchange in winter.

In fall the beaver family begins caching food - branches of favorite foods -- near their lodge. When the water freezes over in winter, they can reach the stored branches from underwater, slipping out of their underwater lodge entrance for a meal. In the photo above you can see the extensive stash of hardwood branches next to the lodge. In summer they much prefer aquatic plants such as the tubers of water lilies.

Beaver have so many cool features and adaptations, enabling their unique lifestyle. Their large skull supports 4 sharp incisors that grow continuously. These teeth make the marks so distinct on beaver-chewed trees and branches.


They use their flat, scaly tail for balance (when gnawing trees), as a rudder while swimming, for warning (the familiar water slap), as a fat reserve (for winter), and for heat exchange. Beavers have several features that allow underwater activity: valves that close off the nose and ears, lips that close behind their teeth so they can feed and carry sticks underwater, features in the back of the mouth that prevent water going down their throat, and a nictitating membrane that protects the eyes. Beavers can spend 5 or 6 minutes underwater.

The beaver's hand-like front feet help them dig and grasp things. Their webbed hind feet provide the obvious aid to swimming and to walk on land, if awkwardly. One of the hind toes is split and is used to groom their thick fur.

Some beavers live along the shores of or in the banks of large water bodies and don't need to build a dam since the water level is naturally deep enough. In smaller water bodies they build a dam to flood an area deep enough to allow underwater winter entrance to their lodge and to reach preferred food supplies. Beaver also build small canals to reach food supplies, floating logs and branches back to the lodge or dam as needed. Their favorite all-time foods are aspen and willow, but they will take other hardwoods and sometimes pine or hemlock. Interestingly, red maple is not a favorite food, it is difficult for them to digest.

Sometimes a beaver fails to drop a tree in the right direction and it gets hung up. I've read nothing to indicate that they can judge which way a tree will fall. One study said that European beavers hang up trees about 15% of the time. That's not bad. You do wonder what the beaver thinks when they make the final gnaw, the tree begins to fall, but then hangs up. It probably gnashes it teeth. Here is one of those hung up trees.


Although not to be deterred, the beaver moves on to the next tree night after night.


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