Geographic ranges of North American birds. American Museum novitates ; no. 2785

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New York, N.Y. : American Museum of Natural History
"The sizes of geographic ranges of North American birds form a 'hollow curve' frequency distribution with most species having relatively small ranges. In this they agree with mammals, but the average range-size (geometric mean of 2 x 10[superscript 6] km[superscript 2) is larger for birds; also the distribution is lognormal for birds but not for mammals. There are more species of birds than of mammals; 1370 species of North American birds and 842 of mammals conformed to the requirements of the analysis. Birds and mammals have similar patterns of general distribution such as roughly parallel latitudinal gradients in diversity and the hollow curve frequency distribution noted above. Because of these similarities and because birds have larger ranges, a larger percentage of the continent's avian species than of its mammalian species may be found in any one local area. Birds differ from mammals in greater prevalence of seasonal migration. However, more birds migrate short distances or not at all than longer distances. A larger percentage (50%) of North American avian species than of mammalian species (13%) occur also outside of North America. Present hypotheses relating sizes of geographic ranges to competition, diversity, age of taxa, eurytopy, niche width, vagility, latitude, abundance, sizes of individuals, and trophic levels are briefly noted. No hypothesis is very satisfactory. However, little attention has been devoted to studies describing or explaining patterns of frequency distributions of areas of different sizes in any group of organisms. The present paper describes the pattern for North American birds, compares them with mammals, and suggests some hypotheses for further testing"--P. [1].
17 p. : ill., maps ; 26 cm.
Includes bibliographical references (p. 16-17).