Beaver tales: Leaving an ecological impact

Though large and common, beavers are seldom seen unless you know where to look. The best time to see beavers is at dusk on a summer evening. And the best place is on quiet water from a kayak or canoe.

Float quietly!

Wildlife usually ignores me when I glide silently and low on the water. Over the years, I’ve had close encounters with deer, ducks, muskrats, great blue herons, snapping turtles, and even river otters while floating quietly. I suspect people are less threatening and more a part of the landscape in a  kayak or canoe than when upright on land.

I remember one evening on a lake in rural Pennsylvania. It was getting dark, and my wife and I were paddling back to the parking lot.  About 20 feet ahead, a beaver broke the surface of the water. We followed it for about 30 seconds. It seemed oblivious to our presence. Then “Smack!”—  a loud splash broke the evening stillness.

Beaver sighting

The beaver slapped its broad, flat tail on the surface of the water, then dove for cover. About two minutes later it resurfaced, slapped another  alarm and submerged. We took the hint and called it a day.

Beavers, the largest rodent in North America, are perfectly suited to a semi-aquatic lifestyle. Adult beavers weigh 25 to 60 pounds and are  protected by dense, waterproof fur.

Underwater vision

Transparent inner eyelids, called nictitating membranes, permit clear underwater vision. Muscular valves close the ears, nose, and mouth while underwater, and their lips close behind huge chisel-like teeth so they can gnaw while submerged.

Large lungs permit beavers to remain under water  up to 15 minutes. Finally, the beaver’s flat tail stores fat, serves as a rudder while swimming, and functions as a communication device.

Furthermore, beavers are consummate environmental engineers. They  build dams to create ponds that provide safe haven from predators and  create habitat for many other aquatic creatures. Everything from brook trout and dragonflies to wood ducks and prothonotary warblers use wetlands  created by beavers.

In the pond behind the dam beavers build a lodge that provides shelter and warmth even through the coldest winter. It also makes a snug nursery  for the three or four precocious kits that are born in May or June following a gestation period of about 107 days.

Beaver lodge

The internal dimensions of a beaver lodge can measure two feet high  and eight feet across. The inner chamber rests just above the waterline and  is connected to the pond by one or more underwater tunnels. The winter temperature inside a well-built lodge rarely drops below freezing.

But not all beavers build dams and lodges. Those that live along wide swiftly flowing rivers that cannot be dammed live in burrows they excavate along the stream bank. In the absence of dams and lodges, the presence of beavers often goes unnoticed.

Ecological impact

The typical beaver that uses logs, branches, rocks, and mud as building materials has had an enormous ecological impact on the face of North  America. Beaver activity influences the type of vegetation that grows within hundreds of yards of the dam. As the vegetation changes, so do animal communities. Across the continent almost every beaver pond follows a predictable pattern.

As the pond grows, the area’s soil chemistry changes and water tolerant trees such as willows and alders, invade. Not surprisingly, the bark  and tender twigs of these trees are favorite beaver foods. The pond itself invites wood ducks, black ducks, muskrats, otters, mink, and trout. Fly  fisherman value the locations of secluded beaver ponds.

Forest returns

Eventually, however, the pond silts in, a process that may take decades. Then the beavers move on. Siltation continues until the pond  disappears, and new ground is born. In about 150 years, just a blink of an ecological eye, the original forest returns.

Beavers also helped early explorers open the western front of North America. Trappers in search of beaver pelts were first to penetrate beyond  the Great Plains. Settlers followed closely in their tracks. The utility, beauty, and warmth of beaver skins molded early American fashion. And the fur trade drove the economies of the towns and trading posts on the western frontier of an emerging nation.