- Since 1970, bird populations in the continental U.S. and Canada have suffered a net loss of 29 percent, or 2.9 billion birds.
- Grassland birds seem to have been hit the hardest: there’s been a 53 percent reduction in grassland-bird populations since 1970; more than 700 million breeding individuals have been lost, and three-quarters of all examined grassland bird species are declining.
- The study did not look into the causes of the bird declines, but the researchers say the patterns of loss in North America are similar to those observed elsewhere in the world, and the causes, including habitat loss, are likely to be similar.
Bird populations are crashing in North America. And it’s not just the rare and threatened species that are disappearing — even the common, seemingly widespread backyard birds like sparrows, warblers and finches are vanishing right under our noses, a new study has found.
Since 1970, bird populations in the continental U.S. and Canada have suffered a net loss of 29 percent, or 2.9 billion birds. Researchers arrived at this staggering number by analyzing close to 50 years of population data for 529 species of birds, gleaned from multiple long-term bird-monitoring data sets.
They also analyzed data recorded by the network of 143 weather radars across the U.S., to track the changes in nighttime spring migration of birds from 2007 and 2017. The radars, which can detect avian migration even in areas where birds are otherwise poorly monitored on the ground, revealed a 14 percent decline in migratory birds since 2007.
North America has a bird crisis, the researchers say. And many bird species could soon head down the path of the passenger pigeon (Ectopistes migratorius), a bird that once numbered in the billions, but silently went extinct by the early 1900s.
“This is a bird emergency with a clear message: the natural world humans depend on is being paved, logged, eroded and polluted. You don’t need to look hard for the metaphor: birds are the canaries in the coal mine that is the earth’s future,” David Yarnold, president and CEO of the National Audubon Society, who was not involved in the study, said in a statement. “This is a full-blown crisis that requires political leadership as well as mass individual action.”
Most of the loss — over 90 percent — occurred across 12 bird families, including sparrows, warblers, blackbirds and finches. But grassland birds seem to have been hit the hardest. Since 1970, there’s been a 53 percent reduction in grassland-bird populations, with 700 million fewer breeding individuals today than in 1970. Nearly 75 percent of all examined grassland bird species are on the decline, the study found.
A few groups, like raptors and wetland birds, saw a net gain in their population over the past five decades. But these increases are not sufficient to offset the overall larger losses, the researchers say.
“Multiple, independent lines of evidence show a massive reduction in the abundance of birds,” Ken Rosenberg, the study’s lead author and a senior scientist at the Cornell Lab of Ornithology and American Bird Conservancy, said in a statement. “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.”
While the study did not look into the causes of the bird declines, the researchers say the patterns of loss in North America are similar to those observed elsewhere in the world, and the causes are likely to be similar.
Take the grassland birds, for example. Widespread conversion of grasslands to farmlands and urban areas, and the extensive use of toxic pesticides in breeding and wintering areas of the birds, are likely responsible for the reduction in grassland bird numbers in North America as they have been across Europe.
Birds are good indicators of environmental health and are among the best monitored groups of animals. Their decline represents just the tip of an iceberg, the researchers say, and could indicate similar losses in other animal groups.
“These data are consistent with what we’re seeing elsewhere with other taxa showing massive declines, including insects and amphibians,” Peter Marra, senior scientist emeritus and former head of the Smithsonian Migratory Bird Center and now director of the Georgetown Environment Initiative at Georgetown University, said in the statement.
“It’s imperative to address immediate and ongoing threats, both because the domino effects can lead to the decay of ecosystems that humans depend on for our own health and livelihoods, and because people all over the world cherish birds in their own right,” Marra added. “Can you imagine a world without birdsong?”
Rosenberg et al. (2019) Decline of the North American avifauna. Science. eaaw1313. doi:10.1126/science.aaw1313.