Thursday, February 2, 2017

Beavers Invade Maynard

Gnawed tree near Ice House Landing, Maynard
(2006 photo) Click on any photo to enlarge.
A beaver family has created a lodge on the north side of the mill pond about 80 yards east of the Sudbury Street bridge, and are destroying trees on Mill & Main property, trees bordering St. Bridget property and also on neighboring private property. Tree damage by other beaver families is evident up and down the Assabet River between the Ben Smith and Powdermill dams. Beavers will walk more than 150 feet from water's edge to take down trees for food and building material. Heavy gauge wire fencing four feet tall is recommended to protect individual trees.

Due to fur trapping, beavers were gone from colonial Massachusetts by 1750, and did not start to repopulate the state until 1930s. When colonial farmers relocated to new areas to start a new village they anticipated finding large, tree-free expanses near streams. These farm-ready spaces had once been beaver ponds. Resident beavers would have moved away after all the surrounding trees have been cut down and eaten. Or else had been trapped for pelts. Unmaintained dams deteriorated and washed out, draining the ponds and leaving fertile meadows.  

While recovery has not been as explosive as for whitetail deer, which now exceed their pre-European population, estimates are that Massachusetts is home to at least 100,000 beavers. The Assabet River National Wildlife Refuge is home to a dozen or more active colonies – all contributors to the wetlands habitat essential to many other species.

Many towns’ Department of Public Works have to deal with beaver management every year. Maynard's DPW has on several occasions brought in licensed trappers to remove beavers from wetlands near the town’s well fields. Homeowners can apply to a town’s Board of Health for an Emergency Permit to trap and kill beavers affecting private property. State law does not allow for relocation, or for that matter, destroying a dam or lodge without a permit.

When beavers are able to find a place to live without disruption, spring brings a litter of about four kits which will remain close to the parent pair for two years, helping out with chores such as dam and lodge maintenance, plus late-fall food storage in the form of underwater piles of branches. This way, food remains accessible under the winter ice. The adult male of the mated pair will create scent mounds marking the family’s territory. This territoriality results in families being no closer than half a mile from each other. If a beaver pond is seen with two lodges it just means the one family in residence upgraded.

Beaver skull purchased from licensed trapper.
Note orange tint to enamel. Click to enlarge.
Our resident adult beavers have no predators. Before the Europeans got here they were hunted by Native Americans, wolves, cougars and black bears. Nowadays, their lifespan in the wild can exceed 20 years, with adults typically weighing 45-65 pounds but known to top 100 pounds. Every spring, the two-year olds, evicted from their parents’ lodges, go a wandering. Summer sightings and new areas of tree damage are probably by these adolescents. Lodges are not always surrounded by water. If the water level is relatively stable the beaver will forego constructing a dam, and instead build a lodge next to shore, referred to as a bank lodge.

The four front wood-gnawing teeth, continually growing, are radically different from the chewing teeth. The enamel of the outer surface incorporates an iron-containing pigment which makes that surface harder and also orange in color. Because the rest of the tooth is a softer dentin material, the teeth resharpen with use.

Beaver skull showing space between
gnawing teeth and chewing teeth
Everyone knows that beavers chop down trees, but the descriptions in school-age appropriate texts omit a few facts. Yes, beavers use mud, rocks and branches to construct dams and lodges. Yes, branch tips and underbark are consumed as food. But did you know that gnawed food is only partially absorbed during passage through a lengthy small intestine? Whatever is left enters an enlarged section of the large intestine, where it undergoes bacterial breakdown. After a day of browsing on greenery, beavers retire to the lodge for the night, where they will defecate, gather up their feces, and eat everything all over again. Coprophagia (yes, it has a name) allows for enhanced energy absorption from the bacterially processed plant fiber, and is practiced by many other herbivores. The next morning the beavers defecate the twice processed material in the water outside the lodge and start the new day.

Beaver damage to large trees.
Beavers sometimes gnaw all the way around the trunk of a large tree, but do not finish the work, so the tree is dead but still standing. One theory is killing large trees will promote growth of new trees, which is what the beavers want to eat. The other theory is dental hygiene - the beavers need to gnaw on hard wood to keep their front teeth from getting too long. These two trees are next to the Assabet River on the Assabet River Walk trail. The bark is chewed to a height of about three feet. Nearby, there are stumps of small trees the beavers cut through and dragged into the river for food. The water level on this part of the river is set by the Powdermill Dam, so beavers have a lodge but no dam of their own.

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