Brian Handwerk for National Geographic News November 23, 2004

November's full moon, coming this Friday, is traditionally called the full beaver moon, because it signals the time to set traps for beavers before swamps freeze.

A gentler interpretation of the name given to the November moon, according to the Farmers' Almanac, is that this is when busy beavers are feverishly preparing their dens for winter.

Whatever the name's origin, the 2004 full beaver moon serves as a spotlight on North America's largest rodent. Harvested and driven from its habitat until it disappeared from much of the northeastern U.S., the beaver is now making such a strong comeback that it is becoming a nuisance in some areas.

From the mid-1600s through the 1800s beaver trapping helped spur European exploration of North America. Beaver pelts became a prized commodity and were traded as currency in many parts of the frontier. Fortunes were made in their fur.

Beavers were pursued so relentlessly that by the early 1900s many beaver populations were in trouble or wiped out. The situation was aggravated by the clearing of much of the beaver's habitat for agriculture.

"In the 1930s they were at a low point," said beaver expert Dietland Mueller-Schwarze of the State University of New York's College of Environmental Science and Forestry in Syracuse. "But the latter half of the century has seen large growth in populatons all over North America."

Multiple factors favored the beaver recovery. Federal and state authorities, supported by hunters and trappers, enacted sustainable harvesting regulations. Beavers were reintroduced into their former range throughout the northeastern U.S., where the decline of agriculture enabled them to thrive and expand.

Meanwhile, plunging demand for pelts at home and abroad has reduced the number of trappers in the field. Some U.S. states have even banned trapping.

Scott Hartman is the national director of membership and state affiliate relations for the National Trappers Association (NTA), which is based in Bedford, Indiana. He notes that the market for furs and pelts dropped precipitously in the mid-1980s and remained depressed until 2000. Since that time it has seen a slow recovery, but profits remain low for the time-intensive pursuit, which is still practiced by an estimated 150,000 U.S. fur trappers.

The reduced trapping pressure has coincided with the longer-term reforestation of former farmlands.

"With the reforestation of our state, the beaver population has rebounded," said wildlife biologist Peter Picone. Picone works for Connecticut's Department of Environmental Protection at the Burlington field office. "In 1800 Connecticut was 75 percent pasture. Today it is 57 percent forested and the [restored] forested habitat is prime for their recovery."

But as beavers flourish and expand, their habitat is increasingly human habitat?and the two mammals often butt heads.

"Nature's Engineers"

Beavers (Castor canadensis) can gnaw through a 6-inch (15-centimeter) tree in 15 minutes. A single busy beaver chews down hundreds of trees per year. The trees are used to build lodges and large dams that provide their aquatic habitat. Dams can range from 2 to 10 feet (2 to 3 meters) in height and stretch more than 100 feet (30 meters) in length.

Streams and lakes are favorite stomping grounds, but water sources like farm ponds, wetlands, and other areas will do, as well.

Picone notes that beavers are among Connecticutt's most problematic animals for humans, likely ranking just behind deer in terms of economic damage. Their tree-felling and large-scale flooding can damage timber and agricultural crops and wash out property and often roads.

"Where humans and beavers can coexist, we encourage it," Picone said. "Beavers create great habitat for other animals. Wood duck, great blue heron, river otter? they all benefit from that habitat that beavers create."

Other benefits include, ironically, flood control through water management, and water storage and purification.

"Everybody sees the negative impact, Mueller-Schwarze said. "People remember the beaver that took down the cherry trees in the [Washington, D.C.] Tidal Basin. The positive effects are harder to see."

The positives are real, but unfortunately for the beavers, so are the negatives.

"The benefits have to be balanced with the damage [beavers cause] to people's property and with flooded roads," Picone said. "It's a tough balance."

Trapping: Cruelty or Conservation?

Solutionssuch as fencing off trees and installing free-flow water devices through damscan mitigate beaver problems and leave habitat intact. But reviews on their effectiveness are mixed.

Another beaver control method is contested for both its results and its application?trapping. As trapping for valuable pelts has declined, nuisance-control trapping has grown. States like Connecticut and New York facilitate the process.

"Here in New York they have a management plan where they want to keep the population limited to 20 or 30 percent of the available [habitat] sites along streams, with food and water, in areas where they won't do damage to human works," Mueller-Schwarze said. "The idea is that when the colony produces young beaver [who go off in search of their own turf], they will have a suitable place to go?the remaining 70 percent of those sites."

The policy is managed by lethal trapping, though Mueller-Schwarze would prefer to see the animals relocated when possible.

The Washington, D.C.-based Humane Society of the United States (HSUS) opposes lethal trapping.

"We oppose the kinds of traps that drown these animals," said biologist John Hadidian, director of HSUS's Urban Wildlife Program. "We oppose the traps that crush them, those that are supposed to break their backs but often don't."

Hadidian argues for better management methods that can help mitigate beaver problems and leave the animals in place with naturally determined numbers.

"We understand that there are people who have trouble dealing with these conflicts, but we don't agree that they need to be lethally disposed of in order to solve these problems," he said. "Even if it was necessary, there are humane ways to do it. These devices that trap them and drown them are inhumane."

NTA's Scott Hartman says that modern traps are a humane way of controlling beaver populations. He notes that in states like Massachusetts, where trapping has been banned, debate rages over the costs and impact, for good or ill, of the policy of not trapping beavers.

"The animal rights folks have made it an emotional issue," he said. "They're dealing mainly with quality of death and we deal with quality of life. You can't stockpile wildlife, you can only have so many animals living in an area. When populations become too high you get disease and you have more animal-human conflict," he said.

For some that conflict's bottom line is defined by dollars and sense.

"It depends how tolerant the local people are," Mueller-Schwarze said of reactions he's seen to beavers in the neighborhood. "Some are excited and some are annoyed, and the same person may tip from one to the other if the damage gets worse. There was a Cornell University study some years ago that determined that the magic number was 400 [U.S.] dollars. People didn't mind up to that point, but after more damage was caused, they often wanted someone to 'take care' of the beavers," he said.