Methodology

Summaries of Population Change for Birds by Habitat

Following the approach developed by Gregory and van Strien (2010), State of the Birds reports focus on composite summaries of population change for collections of species that share common primary habitat or taxonomic affinity. In this report, we provide composite indexes for habitat-obligate species as defined in earlier reports (Grassland, Aridland, Eastern Forest and Western Forest), for several taxonomic-based groups (Shorebirds, Waterbirds, Sea Ducks, and Dabbling/Diving Duck species), and for species on our Tipping Point list with adequate data. Lists of species included in each habitat-obligate group are presented at the bottom of each habitat page in the Results section of this website. Summary trend estimates may be accessed from the Science Base-Catalog at the U.S. Geological Survey.

This report describes long-term population change for 246 species of North American birds (some of which were combined into species pairs for analysis) summarized from five surveys: the North American Breeding Bird Survey (BBS, 169 species, Hostetler et al., 2023), the Christmas Bird Count (CBC, 54 species, Meehan et al., 2022), the Waterfowl Breeding Population and Habitat Survey (WBPHS, 11 species, U.S. Fish and Wildlife Service, 2023), the American Woodcock Singing-ground Survey (SGS, 1 species, Seamans and Rau, 2023), and International Shorebird Surveys (ISS, 9 species, Smith et al., 2023). Earlier versions (or, for ISS, the same version) of all these data sources were used in Rosenberg et al. (2019), and we refer readers to that publication for additional details on the surveys. For each species, annual indices of abundance were obtained from published sources (WBPHS, SGS, ISS) or from data managers (BBS, CBC). In this analysis, we used results from the time period 1970–2022 for all surveys except for the ISS, for which results were only available for 1980–2019.

Statistical analysis of composite summaries follows methods used in earlier State of the Birds reports (e.g., North American Bird Conservation Initiative, 2022), except that we implemented a more accurate incorporation of uncertainty from BBS, CBC, and SGS estimates (using the full Markov Chain Monte Carlo posterior samples instead of making inferences from summary statistics and parametric assumptions). A quantitative description of the statistical model was published in Sauer and Link (2011). It employs a hierarchical model, for which input data are collections of estimates of population change for a species (at the survey-wide scale of summary) from a base year (1970 or 1980) to each subsequent year. For each year, the collection of actual population changes for all species from the base year to the year of interest are assumed to be normally distributed on the log scale, and the latent mean change for the collection is estimated. The model is fit to all years post-base year, and the resulting model-based means form the composite trajectories of change for the species group.

The ratios of the annual indexes of each year, divided by the annual index of the base year, was used to estimate the cumulative change in the species population for that year. Refer to Sauer and Link (2011) for additional details regarding the model and its fitting to BBS and other survey data.

In addition to compiling long-term trend indicators for habitat-obligate and taxonomic-based bird groups, this edition of the State of the Birds report also presents graphics using short-term eBird Trends from the most recent decade (2012–2022). eBird Trends provide a snapshot of annual population change for bird species within 27 x 27 km (16.7 x 16.7 miles) regions, each represented by a circle, for which the size is scaled by number of species (for biome maps) or abundance (for single-species maps). Multi-species maps show the average trend across the species falling into each cell and circle sizes are scaled to the number of species contributing to the average in each cell. These data products are created by the eBird Status and Trends team of data scientists at the Cornell Lab of Ornithology using bird observations submitted by volunteers to eBird. These trends allow scientists and practitioners to see precisely where declines or increases are happening and, thus, provide invaluable information to guide research and conservation.

eBird Trends are produced using a statistical method designed to account for changes in where people go birding and how the identification and detection skills of birders change over time—factors that can make estimating a population trend challenging (Fink et al, 2023). Another novel component of eBird Trends is the inclusion of habitat variables that account for the effect of habitat on population changes. eBird Trends have passed critical statistical tests to ensure they are robust and reliable. An important part of this process is quantifying the uncertainty of the trend estimate. Uncertainty is quantified by an 80% confidence interval. The 80% confidence interval indicates a range of values expected to contain the true (but unknown) trend that is being estimated. If an interval contains zero, then there is low confidence in the estimated direction of the trend (positive or negative). By default, circles with low confidence in the estimated direction are shown in white. For more information: science.ebird.org/en/status-and-trends/faq.

Tipping Point species were identified by scientists, practitioners, and communities as part of the Road to Recovery (R2R) initiative. Assessments relied upon data provided in the Avian Conservation Assessment Database (ACAD)—a database maintained by Partners in Flight (PIF) and housed at Bird Conservancy of the Rockies. Tipping Point species are defined by high vulnerability to extinction and worrisome population declines. R2R assessments also identified three levels of alert to indicate the degree of urgency in addressing these declines: Red-, Orange-, and Yellow-Alert species. See r2rbirds.org/tipping-point-species/ for more information on methods used to identify Tipping Point species.

eBird Status and Trends maps and data are freely available for non-commercial use.

Literature Cited

(except as noted by source-citation footnotes at bottom of pages in the report)

Gregory, R.D., et al. 2010. “Wild bird indicators: Using composite population trends of birds as measures of environmental health.” Ornithological Science 9(1), 3–22. doi.org/10.2326/osj.9.3

Hostetler, J.A., et al.2023. The North American Breeding Bird Survey, analysis results 1966–2022: U.S. Geological Survey data release. doi.org/10.5066/P9IU1UZ6

Meehan, T.D., et al. 2022. Trends in relative abundance for birds wintering in the continental USA and Canada: Audubon Christmas Bird Counts, 1966–2021, version 4.0. National Audubon Society, New York, New York, USA.

North American Bird Conservation Initiative. 2022. The State of the Birds, United States of America, 2022. StateoftheBirds.org/2022

Rosenberg, K.V., et al. 2019. Decline of the North American Avifauna. Science 10.1126/science.aaw1313.

Sauer, J.R., et al. 2011. Analysis of the North American Breeding Bird Survey using hierarchical models. The Auk 128: 87–98.

Seamans, M.E., et al. 2023. American Woodcock population status, 2023. U.S.Fish and Wildlife Service, Laurel, Maryland.

Smith, P.A., et al. 2023. Accelerating declines of North America’s shorebirds signal the need for urgent conservation action. Ornithological Applications 125(2): duad003. doi.org/10.1093/ornithapp/duad003

U.S. Fish and Wildlife Service. 2023. Waterfowl population status, 2023. U.S. Department of the Interior, Washington, D.C.

Fink, D., et al. 2023. A Double Machine Learning Trend Model for Citizen Science Data. Methods in Ecology and Evolution. 14, 2435-2448. doi.org/10.1111/2041-210X.14186

Acknowledgments 

This report was published by the North American Bird Conservation Initiative (NABCI), a forum of government agencies, private organizations, and bird initiatives.

Science Committee: Amanda Rodewald (chair) and Mike Brasher (co-chair); John Alexander; Elisabeth Ammon; Tracy Borneman; Dustin Brewer; Stephen Brown; Jennie Duberstein; Beth Flint; Adam Hannuksela; Kathleen Holland; Jeff Hostetler; Edwin Juarez; Robin Kaler; Chris Latimer; Elva Manquera; Kate Martin; Chris McCreedy; Nicole Michel; Corina Newsome; Andrew Olsen; Marc Romano; Kenneth V. Rosenberg; Brandt Ryder; Rebekah Rylander; John Sauer; Adam Smith; Dena Spatz; Caleb Spiegel; Tice Supplee; Roberta Swift; Eric VanderWerf; Josh Vest; Olivia Wang

Communications Committee: Kathi Borgmann (chair); Madeline Duffy; Nicolas Gonzalez; Matt Harrison; Jordan Rutter; Chris Sebastian; Daniel Sheire; Agatha Szczepaniak; Bradley Wilkinson

Policy Committee: Steve Holmer; Kellis Moss; Erik Schneider; Damien Sharp; Greg Taylor; Jesse Walls

Editor: Gus Axelson; Designer: Jillian Ditner; eBird Trends Map Graphics: Matt Strimas-Mackey; Web Editor: Hugh Powell; Web Design and Content Management: Victoria Campbell, Melissa Penta

Special Thanks:

We are grateful to the following funders for their support of data-driven science through eBird: National Science Foundation, Wolf Creek Charitable Foundation, Leon Levy Foundation, NASA, Institute for Computational Sustainability, PSC, XSEDE. We thank the many contributors, scientists, photographers, and community members whose work and voices are featured in this report.

Suggested Citation 

North American Bird Conservation Initiative. 2025. The State of the Birds, United States of America, 2025. StateoftheBirds.org/2025