Since 1970, bird populations in the U.S. and Canada have declined by 29%, or almost 3 billion birds, signaling a widespread ecological crisis, a study published in the journal Science reveals.
The results show tremendous losses across diverse groups of birds and habitats — from iconic songbirds such as meadowlarks to long-distance migrants like swallows, and backyard birds, including sparrows.
“Multiple, independent lines of evidence show a massive reduction in the abundance of birds,” said Ken Rosenberg, the study’s lead author and a senior scientist at the Cornell Lab of Ornithology. “We expected to see continuing declines of threatened species. But for the first time, the results also showed pervasive losses among common birds across all habitats, including backyard birds.”
The findings, “Decline of the North American avifauna,” showed that of nearly 3 billion birds lost, 90 percent belong to 12 bird families, including sparrows, warblers, finches, and swallows — common, widespread species that play influential roles in food webs and ecosystem functioning, from seed dispersal to pest control.
“This study shows that small changes over a long period of time can have unnoticed but huge impacts,” said Doug Levey, a program director in NSF’s Division of Environmental Biology, which funded the research. “If you go outside pretty much anywhere, you can easily see birds. That gives the impression that they are common, that there isn’t a problem. These authors clearly show that there is a concern and that it’s been slowly growing for a long time.”
Species extinctions have defined the global biodiversity crisis, but extinction begins with loss in abundance of individuals that can result in compositional and functional changes of ecosystems. Using multiple and independent monitoring networks, we report population losses across much of the North American avifauna over 48 years, including once common species and from most biomes. Integration of range-wide population trajectories and size estimates indicates a net loss approaching 3 billion birds, or 29% of 1970 abundance. A continent-wide weather radar network also reveals a similarly steep decline in biomass passage of migrating birds over a recent 10-year period. This loss of bird abundance signals an urgent need to address threats to avert future avifaunal collapse and associated loss of ecosystem integrity, function and services.