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Our Approach
The State of the Birds: Focus on Habitats
To develop this first State of the Birds report for the United States, our team of experts drew upon a variety of sources to determine the conservation status and population trends of more than 800 bird species that occur regularly within the continental U.S., Hawaii, and U.S. oceans.
Healthy bird populations depend on maintenance of both the quality and quantity of habitats. These same habitats provide resources that are essential for human survival and quality of life. Trends in bird populations can give us initial insight into the health of these habitats, and thus provide an indication of environmental sustainability.
We began by assigning each bird species to one of seven primary habitats: oceans, coasts, wetlands, arctic, forests, grasslands, or aridlands. Hawaiian landbirds were treated separately. We defined habitats following the 2008 Heinz Foundation report, The State of the Nation’s Ecosystems.
Birds that are restricted to a single habitat for breeding were defined as habitat obligates, representing an important group of species that are most characteristic of a habitat and that should be most sensitive to environmental problems. Birds found in three or more habitats were considered generalists. We recognized birds that use urban and suburban landscapes as occupying a secondary habitat.
Bird Population Indicators: A Measure of Environmental Health
To assess the health of habitats, we created bird population indicators based on the best available monitoring data for groups of species in each habitat. The concept of wild bird indicators has been applied widely throughout the world in other State of the Birds reports and has been accepted as an important measure of environmental health. Each indicator represents the change in abundance for a group of bird species combined into a single indicator line. We chose 1968 as a base year for these indicators, reflecting the 40-year span of reliable bird-monitoring data for many species, as well as a period of environmental consciousness and habitat protection in the U.S.
Species of Conservation Concern
Because reliable long-term trend data were not available to create
bird population indicators for all U.S. habitats, we also used the
proportion of species of conservation concern in each habitat as a
separate indicator of health or threats to that habitat. Our last line
of defense against extinction is the Federal Endangered Species Act of
1973, which lists 67 bird species as either endangered or threatened
(see PDF chart in Endangered Species
section).
We also recognize an additional 184 species of conservation concern,
based on the U.S. Fish and Wildlife Service’s 2008 Birds of
Conservation Concern, and the 2007 WatchList, produced by the American
Bird Conservancy and the National Audubon Society from information
compiled by bird conservation partnerships. These species show elevated
levels of risk based on small range or population size, high threats,
or declining trends. Proactive conservation efforts aimed at keeping
these species from becoming federally listed constitute the primary
focus of Partners in Flight, the U.S. Shorebird Conservation Plan,
Waterbird Conservation for the Americas, and the North American Bird
Conservation Initiative.
The State of Our Bird Monitoring Data
In this first U.S. State of the Birds report, we relied on long-term
trend data from three primary bird population surveys. The North
American Breeding Bird Survey (BBS), administered by the U.S.
Geological Survey and Canadian Wildlife Service, and conducted at more
than 4,000 sites by volunteer observers, provided data for 365 breeding
species since 1968. For 120 species that breed outside the area of
reliable BBS coverage, but winter primarily within the U.S., we used
trends from the National Audubon Society’s Christmas Bird Count.
Finally, trends for 13 waterfowl species were provided by the U.S. Fish
and Wildlife Service and Canadian Wildlife Service from the Waterfowl
Breeding Population and Habitat Survey, conducted by trained pilots and
wildlife biologists across the northern U.S. and Canada.
Analysis for this State of the Birds report represents the first
integration of long-term results across these three important surveys,
using new statistical techniques developed by scientists at the USGS
and National Audubon Society. Our analysis also highlights the lack of
reliable long-term data for many poorly monitored bird groups, most
notably arctic-nesting shorebirds, colonial seabirds, and oceanic
species. New monitoring efforts for these species and habitats are
essential for future State of the Birds reports.
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