Birds are declining fastest where they were once common

North America’s birds are disappearing, and they’re vanishing at the fastest rate in the places they dominate. A new study using nearly two decades of data from citizen scientists reveals that birds are declining where they should be thriving.

The findings spotlight an ecological emergency but also highlight recovery potential.

The analysis, conducted by researchers at the Cornell Lab of Ornithology, tracked 495 bird species between 2007 and 2021 using over 36 million observations submitted to the eBird platform.

Birds declining across North America

The researchers sought to build a detailed picture of population trends across North America. The result was sobering: in 83% of species, population declines were steepest in areas where the birds were most abundant.

“We’re not just seeing small shifts happening, we’re documenting populations declining where they were once really abundant,” said Alison Johnston, one of the researchers.

“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.”

Birds decline most where they once thrived

Previous studies warned us about overall losses. Since 1970, North America has lost more than 25% of its breeding birds. But knowing where declines are happening is crucial to respond effectively.

Until now, efforts to pinpoint local declines faced a major hurdle: lack of fine-scale, consistent data across species’ ranges.

Johnston’s team tackled this with a machine learning model that could handle vast and varied data inputs. It accounted for human observation behavior, which often distorts raw counts.

The model separated real population changes from observer differences, enabling a clearer picture of regional trends.

The result: a high-resolution map of shifting bird populations, not just across North America, but also Central America and the Caribbean.

Even thriving birds face local losses

While the big picture shows 75% of bird species are in decline – with 65% declining significantly – the local view is more complex.

Nearly every species (97%) shows areas of both gain and loss. That’s a hopeful sign. It suggests some areas offer refuge, while others face stress from climate change and habitat degradation.

“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, co-author of the study.

Even birds considered stable at a regional level may be struggling in their core areas. And species in low-density zones sometimes fare better.

These patterns suggest strongholds are now vulnerable, and previously marginal areas may serve as safe havens.

Role of habitat, climate, and human action

Birds that breed in grasslands and drylands face the sharpest declines. These ecosystems are especially sensitive to habitat disruption and climate shifts.

The findings suggest abundance itself doesn’t guarantee resilience. In fact, pressure may concentrate in places with high population density, degrading quality faster.

Not all regions show loss. The Appalachians and western mountain ranges host stable or growing populations. These areas might offer clues for restoration efforts elsewhere.

“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,” said Johnston.

The scale of bird decline

“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,” said Daniel Fink.

The study ran over 500,000 simulations, requiring more than 6 million hours of computing. That equates to about 85 years of work on a standard laptop. This technical effort was matched by the public’s commitment to citizen science.

“Knowledge is power. 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.

Smarter conservation starts here

The study’s maps and methods help policymakers make sharper choices.

“It’s this kind of small-scale information across broad geographies that has been lacking and it’s exactly what we need to make smart conservation decisions,” said Rodewald.

By seeing exactly where birds are declining or doing well, conservation groups can act with more precision. The insights allow them to focus on recovery where it’s most needed – and most possible.

The message is clear: North America’s birds are in crisis, even in their safest places. But with detailed insight and active stewardship, recovery is within reach.

This research was supported by foundations, NSF grants, and supercomputing resources from Pittsburgh Supercomputing Center and Purdue University. Together, they’ve made a detailed, actionable map for the future of bird conservation.

The study is published in the journal Science.

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