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The Beaver Population in Massachusetts: Myths and Facts

Several pending bills would remove current restrictions on the body-gripping conibear and leghold (sometimes called foothold) traps, which are used to capture fur-bearing mammals, such as beaver and muskrat. This could effectively allow a return to the days of recreational trapping with these inhumane devices, something that 64% of Massachusetts’ voters decried when they voted in favor of a ballot initiative known as the Wildlife Protection Act.

One of the major claims that proponents of bills to remove restrictions on traps make is that these traps are necessary for controlling the beaver population in Massachusetts. The MSPCA disagrees for the following reasons, based on peer-reviewed science.

Claim: The beaver population is exploding and trapping must be expanded to curb it.

  • Populations can only be managed through trapping with Conibear and other body-gripping traps.
  • There has been an increase in property damage complaints due to beavers.
  • Beavers are becoming a nuisance animal instead of a valued resource.
  • The beaver population has skyrocketed to more than 70,000 and will grow exponentially without trapping.


  • Despite the unrestricted recreational trapping that was legal prior to the passage of the Wildlife Protection Act in 1996, the beaver population in Massachusetts nonetheless steadily increased — from 12,800 in 1993 to 24,000 in 1996, according to MassWildlife officials. Clearly, new trapping restrictions passed into law in 1996 do not account for a growing beaver population.
  • When Conibear traps were unrestricted, annual beaver harvest rates hovered around 1,000, the largest take being slightly more than 2,000. Not even a harvest of that size would make a dent in the population. Trapping has never been, and will never be, an effective beaver management tool.
  • Lethal management can in fact stimulate population growth. Studies of exploited (trapped) and unexploited beaver populations have shown that trapping can cause earlier sexual maturation; females in exploited populations gave birth at 24 months of age, whereas females in unexploited populations averaged 32 months before sexual maturity [1].
  • Beavers are territorial; studies indicate ranges of 0.4 to 1.24 beaver families per stream kilometer, and their population will not grow beyond available territory [2].
  • Beaver reproduction is also self-regulating; beavers do not reproduce if populations exceed food supply.
  • Multiple studies also indicate that beaver populations follow a sigmoidal, or S-shaped, pattern, meaning that populations rise and fall over time with or without trapping. For example, a study of New York’s 62,000 acre Allegheny Park revealed that, though beaver trapping has been prohibited in the park for 25 years, the beaver occupancy rate in this park varied from 40% to 60% during these years, never reaching 100% occupancy [3]. Similar findings in California showed population expansion, decline, and stabilization at 35% of maximum capacity [4]. One of the longest-term beaver studies, of the Quabbin Reservation here in Massachusetts, also shows similar trends. Data gathered in 2006 showed a decrease from 2004, “continuing a downward trend that began in 2001”[5].
  • Beavers have predators and other causes of mortality such as automobiles, black bear, coyote, fox, hawk, owl, and natural causes.
  • Property damage is not simply related to overall beaver population; most beavers do not cause any conflicts at all. Property damage occurs — and can be prevented and mitigated — when human habitat and beaver habitat overlap. Sites that are attractive to beavers will be populated by beavers; controlling the conflict is much more cost-effective than trying to control the beaver population.
  • Studies by wildlife biologists examining the “human dimensions” of wildlife management have shown (including a recent survey of Massachusetts residents’ attitudes about beaver) that people’s impressions of beavers as nuisance animals are proportional to both the amount of property damage they have sustained and the amount of information that they have about the benefits of beavers and wetlands. Recommendations for wildlife managers are thus to reduce perceptions of damage, increase awareness of the benefits of beaver, and communicate effectively with property owners about both [6].

Finally, it is worth noting that trapping has declined in Massachusetts, as well as across the country, due to a variety of social, economic, and political factors. According to MassWildlife officials, there are just a few hundred licensed trappers in the state, of which about a third are active. So few trappers cannot exert a population level effect on beavers and should not drive public policy on this matter.

[1] Hodgdon, HE, Social Dynamics Within An Unexploited Beaver Population, Ph.D. Thesis, University of Massachusetts, 1978, p. 144-145.
[2] Ibid., p. 135-137.
[3] Schulte, Bruce, as reported to the MSPCA by Sharon Brown, Biologist, Beavers, Wetlands & Wildlife, 1998.
[4] Taylor, D. Growth, decline, and equilibrium in a beaver population at Sagehen Creek, California, Ph.D. Thesis, University of California, Berkeley, 1970.
[5] Busher, P.E. and Paul J. Lyons. Long-term Population Dynamics of the North American Beaver, Castor Canadensis, on Quabbin Reservation, Massachusetts and Sagehen Creek, California. Beaver Protection, Management and Utilization in North America. Kluwer Academic/Plenum Publishers, 1999.
[6] Enck, J.W. et al, Management Response to Beaver Complaints: Defining Problems and Acceptable Solutions, May 1996, Human Dimensions Research Unit, Cornell University; Loker, C.A., Human Dimensions of Suburban Wildlife Management: Insights from Three Areas of New York State, August 1996, Human Dimensions Research Unit, Cornell University; Loker, C.A., et al, Social acceptability of wildlife management actions in suburban areas: 3 cases from New York, Wildlife Society Bulletin, 1999, 27(1):152-159; Organ, J.F. and Mark R. Ellingwood, Wildlife Stakeholder Acceptance Capacity for Black Bears, Beavers, and Other Beasts in the East, Human Dimensions of Wildlife, 5:63-75, Taylor & Francis, 2000.

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