page_title: North American beaver
section_title: Effects on bird abundance and diversity
hierarchical_section_title: North American beaver / Ecology / Effects on bird abundance and diversity
caption_attribution_description: English: Photo of Canada Goose nesting on beaver lodge in Crawford County, Pennsylvania
context_page_description: The North American beaver is one of two extant beaver species. It is native to North America and introduced in South America and Europe. In the United States and Canada, the species is often referred to simply as "beaver", though this causes some confusion because another distantly related rodent, Aplodontia rufa, is often called the "mountain beaver". Other vernacular names, including American beaver and Canadian beaver, distinguish this species from the other extant beaver species, Castor fiber, which is native to Eurasia. The North American beaver is an official animal symbol of Canada and is the official state mammal of Oregon and New York.
context_section_description: Beavers help waterfowl by creating increased areas of water, and in northerly latitudes, they thaw areas of open water, allowing an earlier nesting season. In a study of Wyoming streams and rivers, watercourses with beavers had 75-fold more ducks than those without.
  Trumpeter swans (Cygnus buccinator) and Canada geese (Branta canadensis) often depend on beaver lodges as nesting sites. Canada's small trumpeter swan population was observed not to nest on large lakes, preferring instead to nest on the smaller lakes and ponds associated with beaver activity.
  Beavers may benefit birds frequenting their ponds in several additional ways. Removal of some pondside trees by beavers increases the density and height of the grass–forb–shrub layer, which enhances waterfowl nesting cover adjacent to ponds. Both forest gaps where trees had been felled by beavers and a "gradual edge" described as a complex transition from pond to forest with intermixed grasses, forbs, saplings, and shrubs are strongly associated with greater migratory bird species richness and abundance. Coppicing of waterside willows and cottonwoods by beavers leads to dense shoot production which provides important cover for birds and the insects on which they feed. Widening of the riparian terrace alongside streams is associated with beaver dams and has been shown to increase riparian bird abundance and diversity, an impact that may be especially important in semiarid climates.
  As trees are drowned by rising beaver impoundments, they become ideal nesting sites for woodpeckers, which carve cavities that attract many other bird species, including flycatchers (Empidonax spp.), tree swallows (Tachycineta bicolor), tits (Paridae spp.), wood ducks (Aix sponsa), goldeneyes (Bucephala spp.), mergansers (Mergus spp.), owls (Tytonidae, Strigidae) and American kestrels (Falco sparverius). Piscivores, including herons (Ardea spp.), grebes (Podicipedidae), cormorants (Phalacrocorax ssp.), American bitterns (Botaurus lentiginosa), great egret (Ardea alba), snowy egret (Egretta thula), mergansers, and belted kingfishers (Megaceryle alcyon), use beaver ponds for fishing. Hooded mergansers (Lophodytes cucullatus), green heron (Butorides virescens), great blue heron (Ardea herodias) and belted kingfisher appeared more frequently in New York wetlands where beaver were active than at sites with no beaver activity.
  By perennializing streams in arid deserts, beavers can create habitat which increases abundance and diversity of riparian-dependent species. For example, such as the upper San Pedro River in southeastern Arizona, reintroduced beavers have created willow and pool habitat which has extended the range of the endangered Southwestern willow flycatcher (Empidonax trailii extimus) with the southernmost verifiable nest recorded in 2005.
caption: Canada goose nest on beaver lodge
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