Assessment of U.S. Birds by Habitat
Because healthy bird populations depend on both the quality and quantity of their habitats, our State of the Birds approach focuses on species that are dependent on a single primary habitat type—we define these species as habitat obligates. For this report, we identified obligate species in oceans, coasts, inland wetlands, forests, aridlands, and grasslands, as well as species found on Hawai`i, Puerto Rico, and the U.S. Virgin Islands, and other U.S. island territories. A listing of species in each habitat and a map of U.S. habitats based on USGS GAP National Land Cover can be found at www.stateofthebirds.org
Bird Population Indicators: A Measure of
The underlying principle of State of the Birds reports is that the health of populations of bird species found only within a habitat reflects the overall health of that habitat. To assess the health of bird populations, we used data from several continental-scale monitoring programs that have provided consistent data since 1968 (or since 1974 for shorebirds). For each obligate species, we assigned a habitat type and estimated the population change up to 2012 with the appropriate survey, then combined the estimates of trends for species in the habitat into a composite estimate of change. This composite estimate of change is used as the bird population indicator for the habitat. The statistical approaches we use for estimation of the bird population indicators were first used in the 2009 State of the Birds report.
Tracking Change in U.S. Bird Populations
In this report, we use information from the North American Breeding Bird Survey, the Audubon Christmas Bird Count, the U.S. Fish and Wildlife Service’s Spring Breeding Ground Waterfowl Survey, and the American Woodcock Singing-ground Survey. A new indicator was developed from monitoring data of migrating shorebirds, using data from the International Shorebird Survey, the Atlantic Canada Shorebird Survey, and the Ontario Shorebird Survey. Detailed information about these surveys and species used in each analysis are provided on the State of the Birds website (www.stateofthebirds.org