Geographic range occupancy of North American birds
Although the geographic range is a fundamental unit of analysis for many macroecological and biogeographical studies, as a representation of the spatial distribution of individuals it is clearly a scale-dependent abstraction. As any amateur naturalist realizes, a species is not guaranteed to be present at every point within the range delimited by a field guide. Geographically extensive survey data such as the North American Breeding Bird Survey (BBS) allow the characterization of distribution patterns within the geographic range. Using BBS data (http://www.pwrc.usgs.gov/bbs/) paired with digital range maps from NatureServe (http://www.natureserve.org/getData/birdMaps.jsp), I calculated a simple measure of range occupancy for 298 species of North American birds. Range occupancy is simply the fraction of sites on which a species is expected to occur based on its range map on which it is actually observed to occur.
Data Set Creators:
NCEAS 9300 : Hurlbert: Exploring the Swiss Cheese Effect
National Center for Ecological Analysis and Synthesis
Geographic range maps were obtained from the NatureServe website at www.natureserve.com. For each species, range occupancy was calculated as the number of survey routes inside the boundary of the range on which a species was found to "occur" divided by the total number of survey routes inside the range. Species' occurrences outside of the geographic range were ignored.
Sampling Area And Frequency:
Temporal extent: A species was defined as being present, "occurring" at a site, if it was observed on at least one survey between 1993 and 2002.
Spatial extent: All of the Breeding Bird Survey routes that were surveyed annually from 1993 to 2002 and that met basic BBS data quality standards (runtype=1 in BBS Weather file) were used to calculate range occupancy.
Taxonomic extent: 298 terrestrial species that are reasonably well censused by BBS methodology. Raptors, owls, waterbirds, shorebirds, seabirds, ducks and geese were excluded.