Between 1970 and 2017, North America witnessed a notable decrease in its bird population, with an estimated loss of around 2.9 billion breeding birds, representing roughly a 29% drop. This figure originated from a 2019 research published in the journal “Science,” spearheaded by Kenneth V. Rosenberg of the Cornell Lab of Ornithology and the American Bird Conservancy. The information underpinning this estimate primarily came from amateur birdwatchers, unpaid volunteers armed with binoculars.
The main data source for this study was the North American Breeding Bird Survey, which monitors population trends for the majority of landbirds. Coordinated by the United States Geological Survey in collaboration with Canadian and Mexican partners, this survey depends on approximately 2,500 volunteer observers. These volunteers traverse specified roadside routes covering 24.5 miles, making 50 stops to note bird sightings or sounds within a quarter-mile radius over three-minute intervals. This undertaking starts half an hour before dawn and continues for about five hours. Since it began in 1966, the survey has grown from 500 routes to around 3,000 surveyed each year.
The research combined range-wide population estimates with 48-year trends for 529 species, roughly 76% of North America’s breeding species, to determine the overall change in numbers. While 38 bird families faced a decline amounting to 3.2 billion, 29 families saw increases of approximately 250 million. The paper also utilized NEXRAD weather radar stations to measure bird biomass, observing a 13.6% decrease over a decade, although this varied across different flyways.
This survey system has its roots in practices such as Audubon’s Christmas Bird Count, which started in 1900, emphasizing simple counting over hunting birds. Contemporary projects like eBird, launched by the Cornell Lab in 2002, further bolster these efforts with comprehensive birding data collection.
Nevertheless, the 2.9 billion figure is frequently misinterpreted as indicating bird deaths through unusual methods or swift extinction rates. Instead, it underscores a decrease in abundance, with many birds still present but in lower quantities. Particularly, habitats such as grasslands saw considerable losses, while regions like wetlands experienced gains, largely due to targeted conservation initiatives supported by hunting revenue.
Ongoing challenges remain, including the bias of counting routes adjacent to roads and the survey’s concentration on breeding adults, which overlooks migratory or wintering issues. Yet, despite possible drawbacks, these volunteer-driven initiatives persist in offering crucial data vital for bird conservation strategies.
The 2019 study spurred action plans like the Road to Recovery initiative. Reports such as the 2025 U.S. State of the Birds highlight urgent conservation needs, including signs of declining duck populations, challenging previous achievements.
Future endeavors will rely on thorough species-level analyses throughout the entire annual cycle and improved radar data, contingent upon sustained volunteer engagement in these essential avian monitoring projects.