Beavers pre­pare for win­ter

Oc­to­ber is an­i­mal fat­ten­ing month

Cape Breton Post - - Community Connections - An­na­marie Hatcher

In the Mi’kmaw cal­en­dar, Oc­to­ber is Wikewiku’s, or an­i­mal fat­ten­ing month.

An­i­mals that will hi­ber­nate through­out the win­ter put on weight at this time of year and birds that mi­grate south add fat as fuel for their long flights.

One of our bio­sphere mam­mals that is fat­ten­ing up at this time of year might sur­prise you. The beaver (Mi’kmaq: ko­pit), that iconic Cana­dian an­i­mal, nei­ther mi­grates nor hi­ber­nates. In fact, if con­di­tions are right, it con­tin­ues to munch on lay­ers of wood over the win­ter as they are avail­able.

As a sort of in­sur­ance and as a boost to the next gen­er­a­tion, the older in­di­vid­u­als also lay down fat stores in the au­tumn which round out their sil­hou­ettes in a most un­usual place, their tails. In fact, the volup­tuous na­ture of a fe­male beaver’s tail is a good pre­dic­tor of the fu­ture health of un­born off­spring. There may be many par­al­lels in our own life sto­ries but I don’t think that I will go there.

Beavers can be found in most of the fresh­wa­ter rivers, streams and wet­lands in the Bras d’Or Lake Bio­sphere. That is where they make their homes. The younger adults, search­ing for a suit­able place to call their own, will also swim in the salty wa­ters of the es­tu­ary. How­ever, they do not stay or feed there. In fact, beavers have been sighted in ocean wa­ters off Nova Sco­tia’s east­ern shore. They are in tran­sit, swim­ming to­ward is­lands that have fresh­wa­ter habi­tat.

Our beavers are semi-aquatic, noc­tur­nal veg­e­tar­i­ans. Most of their diet is made up of tree bark and cam­bium (soft tis­sue grow­ing un­der the bark) and they pre­fer wil­low, maple, birch, beech, po­plar trees and alder shrubs. They build dams as a pro­tec­tion against preda­tors and to pro­vide easy ac­cess to food dur­ing win­ter.

Dur­ing the night they of­ten are “busy as a beaver,” car­ry­ing mud and stone build­ing ma­te­ri­als on their forepaws and tim­ber be­tween their teeth.

The ponds cre­ated by their dams help iso­late the beavers’ lodges, where they live dur­ing the win­ter. Dur­ing the au­tumn they cover their lodges with mud which will freeze dur­ing the win­ter, cre­at­ing a con­crete-like sur­face. That must in­hibit any preda­tors hop­ing for a mid-win­ter feast of beaver.

Un­like other ro­dents, beavers mate for life and stay to­gether for many breed­ing sea­sons. In the safety of a win­ter lodge you can find par­ents and the ado­les­cent off­spring which were born last sea­son.

In the bio­sphere, beavers breed in Jan­uary-Fe­bru­ary. The males have to be “on the ball” be­cause the fe­males are in es­trus for only 12 to 24 hours. The fe­males de­liver be­tween two to six new­born kits about 3.5 months later. Beavers start re­pro­duc­ing when they are about three years old.

When the new lit­ter is born, the ado­les­cents are launched into the world on their own and they seek their own space to build a dam and a lodge.

There are of­ten strong feel­ings about the land­scape changes that a beaver’s build­ing ac­tiv­i­ties can pro­duce, par­tic­u­larly among landown­ers who dis­cover new ar­eas of flood­ing. How­ever, Mother Earth of­ten adapts to these changes in a pos­i­tive way.

For ex­am­ple, beaver ponds can en­hance ground­wa­ter recharge by act­ing as stor­age reser­voirs. They pro­vide crit­i­cal habi­tat for many species of res­i­dent and migrating wa­ter­fowl. They pro­vide habi­tat and food for salmon and trout dur­ing dry pe­ri­ods and se­vere win­ters. Long-stand­ing beaver dams can in­crease di­ver­sity of trees and shrubs in forested ar­eas near the wa­ter’s edge. In some cases, this en­hance­ment has been shown to have a greater im­pact than the neg­a­tive ef­fect of the beavers’ har­vest­ing ac­tiv­i­ties.

Beavers are be­ing re-in­tro­duced in many ar­eas be­cause of their ben­e­fi­cial im­pacts on stream ecosys­tems.

Now, let’s get back to that tail. The beaver’s tail can be up to 30 cm long and is a multi-use body part. It has a tough, thick outer layer of skin which has very lit­tle hair. It is flex­i­ble and sup­ported by a strong mus­cu­lar frame­work which makes it use­ful as a rud­der for swim­ming and a prop for sit­ting. It is also used to sig­nal other beavers. When alarmed, they use their tails to slap the wa­ter, warn­ing oth­ers to take refuge un­der the wa­ter.

In au­tumn, fe­male beavers are at their chub­bi­est, along with many other an­i­mals of the bio­sphere. Their volup­tuous tails de­crease in vol­ume twofold from au­tumn to spring (Aek­suik, 1970) as they me­tab­o­lize the fat re­serves. That fat reser­voir feeds the de­vel­op­ing em­bryo in the over­win­ter­ing, preg­nant fe­males. It has been shown that the fe­males with the fat­test tails in au­tumn are most likely to pro­duce a healthy lit­ter in spring.

So, as you hike near beaver ponds in the bio­sphere this au­tumn, imag­ine what the land­scape will look like in mid-win­ter and pic­ture the fam­ily of beavers safe in their lodge. They will have a stash of drowned tree branches and a store of fat to sus­tain them un­til spring.

In­for­ma­tion from the Jour­nal of Mam­mol­ogy (51(1)) pub­lished in Fe­bru­ary 1970, writ­ten by Michael Alek­siuk, and ti­tled “The func­tion of the tail as a fat stor­age de­pot in the beaver (Cas­tor Canaden­sis),” was used to write this col­umn.

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