USGS · 5220871
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C.S. Robbins. 1977. Data bank of North American breeding bird censuses. https://pubs.usgs.gov/publication/5220871
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Since the Breeding Bird Survey provides an annual quantitative sample of about 75% of the 1? blocks of latitude and longitude in every state except Alaska and Hawaii, and 47% of the 1/2? blocks (equivalent on the average to a 48 km square), no national Atlas based on merely presence or absence has been contemplated. Conventional atlases are in progress in the states of Maryland (2.5 km), Massaohusetts (5 km) and Vermont (5 km) and in parts of 3 other states. Quantitative studies including mapping have been published for North Dakota (10 km) and are in progress in Wyoming (1?). A Montana project (1?) is continuing.
Continental populations of most bird species have remained quite stable since 1966, but there have been many regional changes associated with migration disasters, breeding failures and range expansions, and a few dramatic increases in populations of introduced species. These changes often are better represented by curvilinear than by linear regressions.
Island biogeography concepts applied to breeding bird populations of woodlots clearly explain why certain passerine species typical of tracts of 1 km2 or more are absent from tracts one-half or one-quarter that size. Many 'natural areas' now being preserved are too small to support the complete complement of nesting species; this is partly because little knowledge of the minimum areas required is available to the agencies and individuals making the decisions