Beaver populations and their relation to wetland habitat and breeding waterfowl in Maine

Abstract

The influence of beaver (Castor canadensis) trapping on beaver and waterfowl densities and wetland habitat is not well understood, and this information is needed by managers trying to balance beaver densities and harvest and complaints of nuisance beaver with the abundance of wetlands and waterfowl. During 1988–92 in south-central Maine, we determined the density of beaver colonies and beaver harvest, wetland characteristics, and density of breeding pairs of waterfowl on a 111-km2 site recently closed to beaver trapping and a similar site open to trapping. Density of beaver colonies increased from 0.15 to 0.32/km2 (113%) on the untrapped site but changed little (0.19–0.20/km2) on the trapped site. The number of beaver dams maintained by beaver and the density of beaver colonies were correlated on the untrapped site (r=0.99, n=4,P=0.009) but not on the trapped site (r=−0.18, n=4,P=0.820). Number of wetlands was correlated with the density of beaver colonies during 1989–92 on the untrapped site (r=0.92, n=4,P=0.081) but not on the trapped site (r=−0.13, n=4,P=0.875). Total surface area of water on the untrapped site increased from 115 to 158 ha (36%); surface area of water remained stable on the trapped area. Species of waterfowl that increased on the untrapped site included Canada geese (Branta canadensis) (4–9/100 km2), hooded mergansers (Lophodytes cucullatus) (23–29/100 km2), and mallards (Anas platyrhynchos) (7–12/100 km2). Numbers of wetlands used by pairs of each species of waterfowl increased on the untrapped site. Overall, a ≥1-year closure of beaver trapping is sufficient to increase the density of beaver colonies, whereas a 2–3 year closure is necessary to increase wetland habitat. More than 3–4 years may be required to begin influencing the density of waterfowl and number of wetlands used by waterfowl.