North American bird populations are declining most severely in areas where they should be thriving, according to a groundbreaking study published May 1 in Science.

Researchers from the Cornell Lab of Ornithology set out to develop reliable information about where birds are increasing or decreasing across North America, but the patterns they uncovered were startling.

Birds are declining most severely where they are most abundant – the very places where they should be thriving. Of the species they examined, 83% are losing a larger percentage of their population where they are most plentiful.

“We’re not just seeing small shifts happening – we’re documenting populations declining where they were once really abundant,” said Alison Johnston, lead author and ecological statistician who initiated this study as a research associate at the Cornell Lab of Ornithology. “Locations that once provided ideal habitat and climate for these species are no longer suitable. I think this is indicative of more major shifts happening for the nature that’s around us.”

Johnston is now a faculty member at the University of St. Andrews, Scotland.

The Lab of Ornithology team analyzed 36 million bird observations that birdwatchers shared to the Cornell Lab’s eBird program, along with multiple environmental variables derived from high-resolution satellite imagery for 495 bird species across North America from 2007–2021.

This news follows on the heels of other recent research that documented widespread losses of birds in North America. The 2025 U.S. State of the Birds report showed bird declines in almost every biome in the nation. And a 2019 paper published in Science reported a cumulative population loss of nearly 3 billion birds in Canada and the U.S. since 1970. “The 2019 paper was telling us that we have an emergency, and now with this work we have the information needed to create an emergency response plan,” said Johnston.

The current research features recent bird population trends at 27 km by 27 km scales, the smallest parcels of land ever attempted for an analysis across such a large geographic area.

“This is the first time we’ve had fine scale information on population changes across such broad spatial extents and across entire ranges of species. And that provides us a better lens to understand the changes that are happening with bird populations,” said Amanda Rodewald, Garvin Professor in the Department of Natural Resources in the College of Agriculture and Life Sciences, and faculty director of the Center for Avian Population Studies at the Cornell Lab of Ornithology.

Previously national and continental monitoring programs could estimate population trends only across entire ranges, regions or states and provinces. But with advances in machine learning and the accumulation of vast amounts of data from participatory scientists, researchers can look at how well species are doing in areas about the size of New York City.

Some species appear to be doing well across their range or within a region, but are faring very poorly in specific locations within those regions.

“The super interesting thing is, for almost all species, we found areas of population increases and decreases,” said Johnston. “This spatial variation in population trends has been previously invisible when looking at broader regional summaries.”

Areas where populations are increasing are the bright spots, Johnston said. “Areas where species are increasing where they're at low abundance may be places where conservation has been successful and populations are recovering, or they may point to locations where there may be potential for recovery.”

The study’s detailed mapping of population changes will help conservation organizations and policymakers better target their efforts to protect declining bird species, which, according to the authors, is sorely needed to help reverse the declining population trends.

“It’s this small-scale information across broad geographies that has been lacking, and it’s exactly what we need to make smart conservation decisions,” Rodewald said. “These data products give us a new lens to detect and diagnose population declines and to respond to them in a way that’s strategic, precise and flexible. That’s a game changer for conservation.”

The research also reveals the power of participatory science data. “Because of the volunteers that engage in programs like eBird, because of their enthusiasm and engagement, and generosity of time, we now know more about bird populations and more about the environment than we ever have before,” said Rodewald.

“Without the massive amount of data available from eBird, we would not have been able to complete this study,” said Daniel Fink, a senior research associate and statistician at the Cornell Lab of Ornithology. But alongside all the data comes analytical challenges, he said.

“We employed causal machine-learning models and novel statistical methodologies that allowed us to estimate changes in populations with high spatial resolution while also accounting for biases that come from changes in how and where people go birding,” Fink said. To ensure the reliability of the data the team ran over a half-million simulations, stacking up more than 6 million hours of computing, which would take about 85 years to run on a standard laptop computer.

The research was funded by The Leon Levy Foundation, The Wolf Creek Foundation and the National Science Foundation.

Kathi Borgmann is communications manager for the Cornell Lab of Ornithology.