Our Living Resources — Birils 



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Temperate Domain provides breeding areas for 

 20 species wiiile only 12 breed in the Dry 

 Domain (Fig. 1 ). The number of species breed- 

 ing within the domains in the West generally 

 exceeds those breeding east of the Continental 

 Divide, even though the eastern area is much 

 larger. 



Western North American shorebirds nest in a 

 variety of habitats, although most species (53%) 

 are restricted to either coastal or interior wet- 

 lands (Page and Gill 1994). About a third of the 

 species nest primarily on uplands, especially 

 Arctic and subarctic tundra and dry temperate 

 grasslands. 



Wintering 



Thirty-six (70%) of the continent's breeding 

 species winter in western North America, 

 including seven that are restricted to the region 

 (Table). The continental distribution of species 

 shifts southward in winter, but numbers are still 

 higher in the West than in the East (Fig. 1 ). Only 

 4 of the 37 species breeding in the Polar 

 Domain of western North America remain there 

 during winter. About 30 species spend the win- 

 ter in the Humid Temperate and Dry domains. 

 Populations of 12 (25%) of western Noi1h 

 America's breeding species spend the winter 

 entirely on other continents or throughout 

 Oceania (,v(^(^ glossary; Table). 



Most shorebirds use a much broader range 

 of habitats during winter than during the breed- 

 ing period. All species use one or more coastal 

 habitats in winter and two-thirds of the species 

 also use interior habitats (Page and Gill 1994). 

 Wetlands, the single-most important habitat 

 both along the coast and in the interior of west- 

 em North America, are used by about 80% of all 

 species. Sandy and rocky shorelines along the 

 Pacific coast are also important habitats and are 

 used by about a quarter of the species (Page and 

 Gill 1994). 



Migrating 



All species of North American shorebirds 

 are migratory to some degree, with the possible 

 exception of both species of oystercatchers and 

 Wilson's plover; they are not migratory in the 

 true sense but do make short, local movements. 

 Shorebirds migrate in spring and fall over three 

 broadly defined corridors encompassing the 

 western, central, and eastern portions of the 

 continent to wintering areas in North, Central, 

 and South America (Morrison and Myers 1989). 

 Other migratory corridors funnel Arctic breed- 

 ers from western North America across the 

 Pacific Ocean to wintering areas in Asia, 

 Australasia, and Oceania {see glossary; Gill and 

 Handel 1981; Handel and Gill 1992b; Page and 

 Gill 1994). The distances traveled between 



breeding and wintering grounds vary greatly 

 within and among species, often exceeding 

 8,000 km (5,000 mi) for such species as 

 Hudsonian and bar-tailed godwits. 



Wetlands are the most important habitat 

 used by shorebirds during spring and fall migra- 

 tions. Throughout western North America about 

 140 discrete wetlands and several additional 

 wetland complexes (e.g.. Central Valley of 

 California) have been identified as being impor- 

 tant to shorebirds during these periods (Fig. 2). 

 Most staging areas (85%) host populations of 

 1,000-10,000 birds, but 18 sites support 

 100,000-1 million shorebirds during the peak of 

 migration (Fig. 2). Because shorebirds use dif- 

 ferent migration pathways and strategies during 

 spring and fall, the locations of critical staging 

 areas shift between the two seasons (Fig. 2). 



Status and Trends 



Size of Populations 



Population estimates exist for only about a 

 quarter of the species that breed or winter in 

 western North America (Table), and even these 

 few vary widely in terms of statistical rigor and 

 precision. These estimates range between 



Fig. 1. Number of stiorebird 

 species regularly breeding and 

 wintering within ttiree broad eco- 

 logical domains of Nortin America 

 west and east of tfie Continental 

 Divide (dastied line). 



