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North American birds most closely resemble those of Eurasia, which was connected to the continent as part of the supercontinent Laurasia until around 60 million years ago.〔(【引用サイトリンク】title=Historical perspective )〕 Many groups occur throughout the Northern Hemisphere and worldwide. However some groups unique to the New World have also arisen; those represented in this list are the hummingbirds, the New World vultures, the New World quail, the tyrant flycatchers, the vireos, the mimids, the New World warblers, the tanagers, the cardinals and the icterids. Several common birds in North America, such as the house sparrow, the rock pigeon, the European starling and the mute swan are introduced species, meaning that they are not native to this continent but were brought here by humans from Europe or elsewhere. Introduced species are marked on this list as (I). There may be species that have individual escapees or small feral populations in North America that are not on this list. This is especially true of birds that are commonly held as pets, such as parrots and finches. One species, the cattle egret, was historically an African bird. In the 20th century this bird colonized North America and is now found throughout the lower 48 states of the United States. The cattle egret is the only Old World bird to establish itself in North America in historical times without being introduced by humans. As such, it is not marked as introduced on this list. Neither is the glossy ibis, which probably had a similar history. The status of one bird on the North American list, the ivory-billed woodpecker, is controversial. Until 2005 this bird was widely considered to be extinct. In April of that year, it was reported that at least one adult male bird had been sighted in the Cache River National Wildlife Refuge in Arkansas. This report however, has not been universally accepted, and the American Birding Association still lists the ivory-billed woodpecker as extinct.〔(【引用サイトリンク】title=ABA checklist codes )〕 The definition of the area covered by a list of "North American" birds is somewhat subjective. The original list published by the American Ornithologists' Union (AOU) in 1886 covered birds found in North America north of Mexico, and included Baja California, Bermuda and Greenland. In 1983, the area was expanded to include all of Mexico, Central America south through Panama, the West Indies and the Hawaiian Islands, while Greenland was dropped. This expansion more than doubled the number of birds on the AOU list. Other organizations, such as the American Birding Association (ABA), use a smaller area: the current ABA area includes the 49 continental states of the US, Canada and the French islands of Saint-Pierre and Miquelon, plus surrounding waters.〔(【引用サイトリンク】title=ABA area )〕 It does not include Greenland, Bermuda, the Bahamas or the Hawaiian Islands.〔 This article is based on a checklist used by the ABA, which used by most field guides for North American birds, and is complete up to November 2010. Since the ABA follows the AOU on taxonomical matters, the AOU's list is used to settle questions of taxonomy. __NOTOC__ ==Condition of bird population== A study by the National Audubon Society has found that populations of some the most common birds in North America have plummeted since 1967, with some species showing a decline of 80 percent. The study also found that California species were particularly affected, with population declines of 75 to 96 percent for several species, including the northern pintail, horned lark and loggerhead shrike. The decline may be due to loss of habitat to urban sprawl, especially grasslands, forests and wetlands, energy development and industrialized agriculture. Climate change could compound losses in the future.〔(U.S. bird populations plummet ), by Rhett A. Butler, mongabay.com, June 14, 2007.〕〔(Common bird species in dramatic decline: A new Audubon study is one of the most comprehensive looks at bird-population trends in North America ), By Mark Clayton, ''The Christian Science Monitor'', June 15, 2007.〕〔(Disappearing common birds send environmental wake-up call ), Audubon press release, June 14, 2007.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「List of birds of Canada and the United States」の詳細全文を読む スポンサード リンク
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