Due to habitat loss, pesticides, and more, North America’s springs are more silent than ever.
You might not notice it while hiking through the woods or strolling through a city park, but according to a new study, bird populations across North America are in a state of quiet freefall.
In fact, compared with bird counts from 1970, scientists now estimate that the United States and Canada, which are home to 760 bird species, have lost around three billion birds.
The study, published today in the journal Science, analyzed a combination of long-term population surveys as well as weather radar data to tease out the trend. Overall, the researchers discovered that birds found in grasslands—including well-known families such as sparrows, warblers, blackbirds, and finches—have been hit hardest, with their populations cut 53 percent over the last 48 years. (Read why birds matter in National Geographic magazine.)
With nearly three-quarters of all grassland species experiencing decline, it seems these biomes, which include farmers’ fields, are especially vulnerable to habitat loss and exposure to toxic pesticides. But plummeting bird numbers may also be linked to huge drops in insect populations—an important avian prey, the researchers say.
“We should take it as staggering, devastating news,” says study senior author Peter Marra, director of the Georgetown Environment Initiative at Georgetown University.
That’s because birds are crucial to the healthy functioning of ecosystems. Not only do our feathered friends help keep crop pests and other insects in check, but they also play critical roles in distributing seeds, disposing of rotting carcasses, and even pollinating plants.
What’s killing birds?
For the study, Marra and colleagues analyzed range-wide population estimates across 529 species of birds, some of which provided around half a century’s worth of data. They also included biomass estimates from weather radar, which can actually detect birds as they take to the skies at night to complete their biannual migrations. This helped the team calculate how populations have changed in areas where on-the-ground monitoring is more sparse, like the far north.