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
If
you are aware of any important scientific publications
about the effects of beaver engineering on birds that were omitted
from this review, or have other suggestions for improving it, please
contact the author at his e-mail address:
director {at} ecology.info
©
Copyright 2003-2012
Ecology Online Sweden. All rights reserved.
Back
to the first page of "Ecology of the
Beaver."