Beaver and Birds

Note: This online review is updated and revised continuously, as soon as results of new scientific research become available.  It therefore presents state-of-the-art information on the topic it covers.

When beaver (Castor canadensis and Castor fiber) build dams, ponds, canals, lodges, and kill trees by felling, flooding or girdling, some species of birds are benefited and become more numerous. Other birds are unaffected or decrease in abundance.  In this report, we review the various species of birds affected by beaver engineering.   

Waterfowl

The construction of a beaver dam creates a pond that attracts and supports waterfowl.  In Maine, McCall et al. (1996) compared waterfowl living on two 111 square kilometer study sites, one where beaver were trapped and one where trapping was prohibited.  On the site where beaver were trapped the density of beaver colonies changed little, while on the untrapped site the density of beaver colonies doubled over the four-year study period.  Consequently, the number of dams maintained by beaver increased 64% on the untrapped site, but only 8% on the trapped site.  Pairs of Canada Geese (Branta canadensis) and Mallards (Anas platyrhynchos) doubled in number on the untrapped site, but remained virtually unchanged on the trapped site.  Many Canada Geese used abandoned beaver lodges as nest sites.

The Wood Duck (Aix sponsa) is especially associated with beaver ponds and often increases in numbers when beaver expand their populations and build more dams.  For example, in Bear Mountain State Park, New York, the Wood Duck was virtually unknown as a breeder in 1920.  Over the next twenty years, however, beaver invaded the park and the Wood Duck followed this "engineer."  By 1940, almost every beaver pond in the park had a pair of nesting Wood Ducks (Carr 1940). 

Other studies confirm these observations.  In forested areas of southern Ontario, Wood Ducks preferred beaver ponds to all other wetland habitats (Merendino et al. 1995).  However, new active beaver ponds are preferred to older ones (Brown and Parsons 1979).  In the Appalachian Plateau region of South-central New York, for example, Wood Ducks were found at 52% of active beaver ponds, 21% of abandoned beaver ponds, and at 0% of wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver" (Grover and Baldassarre 1995).  Nevers (1968) suggested that the recovery of the entire USA Wood Duck population from very low numbers in the early Twentieth Century, was due to the recovery of the North American beaver population and the resulting increase in the number of beaver ponds.

Also in the Appalachian Plateau region of New York, Hooded Mergansers (Lophodytes cucullatus) were found more often at active beaver ponds than at inactive beaver ponds or at the wetlands with no recent record of beaver occupation (Grover and Baldassarre 1995). 

When beaver occupied wetlands in Finland and their dam-building created flooding, the Green-winged Teal (Anas crecca) became more numerous (Nummi and Poysa 1997).  In contrast, the Mallard did not increase or decrease in numbers.  Broods of the Green-winged Teal, Mallard and Goldeneye (Bucephala clangula) all foraged in beaver ponds more often than expected, as did juvenile Green-winged Teal and Goldeneye (Nummi and Pöysä 1995).

Herons

During spring in the Appalachian Plateau region of New York, Great Blue Herons (Ardea herodias) were 12 times more likely to be found at active beaver ponds than at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver," and 3 times more likely to be found at active beaver ponds than at abandoned beaver ponds (Grover and Baldassarre 1995).  American Bitterns (Botaurus lentiginosus) and Green-backed Herons (Butorides striatus) also preferred active beaver ponds to abandoned beaver ponds and the wetlands with no recent record of beaver occupation (Grover and Baldassarre 1995).

Upland Gamebirds

During May and June, Ruffed Grouse (Bonasa umbellus), Wild Turkey (Meleagris gallopavo) and American Woodcock (Scolopax minor) were seen more frequently at beaver ponds than at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver"  (Grover and Baldassarre 1995).

Woodpeckers

In Bear Mountain State Park, New York, Carr (1940) reported that forests at beaver ponds were the "principal breeding area" of the Pileated Woodpecker (Dryocopus pileatus).  To the west, in the Appalachian Plateau region of New York during May and June, Pileated Woodpeckers were 4 to 5 times more likely to be found at active or inactive beaver ponds, than at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver" (Grover and Baldassarre 1995).  The larger the beaver pond, the more likely a Pileated Woodpecker would be found in the trees there (Grover and Baldassarre 1995).  During winter, however, Pileated Woodpeckers were 3 times more likely to be found at the wetlands with no recent record of beaver occupation than at the active beaver ponds (Grover and Baldassarre 1995).

In Tierra del Fuego, where beaver have been introduced by humans, the  Magellanic Woodpecker (Campephilus magellanicus) forages more frequently near beaver ponds (McBride 2000, Vergara and Schlatter 2004).

Kingfishers

During May and June, Belted Kingfishers (Ceryle alcyon) were seen more frequently at active and inactive beaver ponds than at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver" (Grover and Baldassarre 1995).

Raptors

During censuses in the Appalachian Plateau region of New York, 12 Accipiter hawks (Cooper's Hawk Accipiter cooperii and Sharp-shinned Hawk Accipiter striatus) were seen, all at active beaver ponds (Grover and Baldassarre 1995).  In contrast, no Accipiter hawks were seen at inactive beaver ponds or at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver" (Grover and Baldassarre 1995). 

The Osprey (Pandion haliaetus) is a fish-eating raptor that builds large treetop nests in exposed locations.  A favorite site for Ospreys to build their nests is in the "dead tops of older trees or snags in beaver swamps" (Ewins 1997). 

Swallows

During spring in the Appalachian Plateau region of New York, Tree Swallows (Tachycineta bicolor) and Barn Swallows (Hirundo rustica) were 3 to 4 times more likely to be found at active or inactive beaver ponds than at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver" (Grover and Baldassarre 1995).  The larger the beaver pond, the more likely that these swallows would be found around it (Grover and Baldassarre 1995).  The Bank Swallow (Riparia riparia) and Northern Rough-winged Swallow (Stelgidopteryx serripennis) were recorded only at active beaver ponds, and were absent from inactive beaver ponds and the wetlands with no recent record of beaver occupation (Grover and Baldassarre 1995).

Nuthatches and Creepers

During spring in the Appalachian Plateau region of New York, Red-breasted Nuthatches (Sitta canadensis) were more likely to be found in trees at active or inactive beaver ponds than at wetlands with no recent record of beaver occupation but which "contained appropriate cover types and topographical features suitable for beaver"  (Grover and Baldassarre 1995).  In contrast, White-breasted Nuthatches (Sitta carolinensis) were more likely to be found at the wetlands with no recent record of beaver occupation, than at active or inactive beaver ponds (Grover and Baldassarre 1995).  In winter, Red-breasted Nuthatches continued to prefer active and inactive beaver ponds, while White-breasted Nuthatches foraged predominantly at the wetlands with no recent record of beaver occupation and at active beaver ponds, largely avoiding inactive beaver ponds (Grover and Baldassarre 1995). 

The Brown Creeper (Certhia americana) showed no preference for beaver ponds nor for wetlands with no recent record of beaver occupation (Grover and Baldassarre 1995).

Concluding Remarks

Although many birds are affected by the engineering activities of beaver, the exact mechanisms by which they are benefited or harmed is usually unknown, and a variety of direct and indirect interactions can be postulated to explain changes in abundance. 

For example, the beneficial association of Wood Ducks with beaver could be explained by one or more of the following hypotheses:  (1) Since Wood Ducks nest in large tree holes, and Pileated Woodpeckers excavate large holes in trees, the increased number of Pileated Woodpeckers at beaver ponds might result in there being more nesting sites available to Wood Ducks at beaver ponds; (2) Beaver ponds might have more food for Wood Ducks; (3)  Beaver ponds have more vegetative cover, and this cover protects ducklings and their parents from predators.  Newly-flooded beaver ponds in particular usually have a canopy of trees and shrubs over the water that can make it harder for raptors to detect ducklings (Hepp and Hair 1977, Brown and Parsons 1979).  Field experiments are needed to determine which of these factors, if any, are responsible for the increased numbers of Wood Ducks at active beaver ponds.

Click the following links to learn more about the effects of beaver engineering on wildlife: 
frogs and salamanders, lizards, turtles and snakes, invertebrates, trees.
Click this link for the introductory review: Ecology of the Beaver.

References

Brown MK, Parsons G.R.  (1979)  Waterfowl production on beaver flowages in a part of New York.  New York Fish and Game Journal 26: 142-153

Carr WH (1940)  Beaver and birds.  Bird-Lore 42: 141-146

Ewins PJ  (1997)  Osprey (Pandion haliaetus) populations in forested areas of North America: Changes, their causes and management recommendations.  Journal of Raptor Research 31: 138-150

Grover AM, Baldassarre GA  (1995)  Bird species richness within beaver ponds in South-central New York.  Wetlands 15: 108-118

Hepp GR, Hair JD  (1977)  Wood Duck mobility and utilization of beaver pond habitats.  Proceedings of the Annual Conference of the S.E. Association of Fish and Wildlife Agencies 31: 216-225

McBride P  (2000)  Magellanic Woodpecker (Campephilus magellanicus) habitat selection in deciduous Nothofagus forests of Tierra del Fuego.  MS Thesis, Western Washington University, Bellingham, Washington.

Merendino MT, McCullough GB, North NR  (1995)  Wetland availability and use by breeding waterfowl in southern Ontario.  Journal of Wildlife Management 59: 527-532

McCall TC, Hodgman TP, Diefenbach DR, Owen RB  (1996)  Beaver populations and their relation to wetland habitat and breeding waterfowl in Maine.  Wetlands 16: 163-172

Nevers HP  (1968)  Waterfowl utilization of beaver impoundments in southeastern New Hampshire.  Transactions of the Northeast Fish and Wildlife Conference 25: 105-120

Nummi P, Poysa H  (1997)  Population and community level responses in Anas-species to patch disturbance caused by an ecosystem engineer, the beaver.  Ecography 20: 580-584

Nummi, Poysa H  (1997)  Habitat use by different-aged duck broods and juvenile ducks.  Wildlife Biology 1:181-187

Vergara P, Schlatter RP  (2004)  Magellanic Woodpecker (Campephilus magellanicus) abundance and foraging in Tierra del Fuego, Chile.  Journal of Ornithology 145: 343-351

Information about this Review

The author is:  Dr. Paul D. Haemig (PhD in Animal Ecology)

The photograph at the top of the page was taken by Pam Roth (USA). It shows a Great Blue Heron, one of the bird taxa that benefits from beaver engineering.

The proper citation is:

Haemig PD  2012   Beaver and Birds.  ECOLOGY.INFO #16