If your backyard bird feeder seems a little less popular these days, it's not your imagination.

The number of birds in the U.S. and Canada has plummeted over the past 50 years, dropping by 29%, according to a study published in the journal Science. That's an overall decline of 2.9 billion birds since 1970.

The study found there were large losses for every type of bird, from songbirds to those that migrate long distances.

"Multiple, independent lines of evidence show a massive reduction in the abundance of birds," lead author Ken Rosenberg, 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."

For the analysis, researchers included citizen scientist data from information collections such as the North American Breeding Bird Survey and the Audubon Christmas Bird Count. They also used data from 143 weather radar stations to look for declines in migratory bird populations. Additionally, they studied 50 years of data collected from on-the-ground monitoring.

Grassland birds, such as meadowlarks and sparrows, were particularly affected. They experienced a 53% drop in population — more than 720 million birds — since 1970. So many of these birds have likely disappeared due to modern agriculture and development, as well as pesticide use.

"Every field that's plowed under, and every wetland area that's drained, you lose the birds in that area," Rosenberg told The New York Times.

Shorebirds were also hard hit because of their sensitive coastal habitats. Their populations were already "dangerously low," researchers said, but they've since lost more than one-third of their numbers.

The researchers tracked spring migration using radar in the night skies. They found that in just the past decade, it dropped by 14%.

"These data are consistent with what we're seeing elsewhere with other taxa showing massive declines, including insects and amphibians," said coauthor 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.

"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. Can you imagine a world without birdsong?"

Success stories

It wasn't all bad news, as researchers found a few promising bright spots.

They said waterfowl, like ducks, geese and swans, have made a "remarkable recovery" over the past 50 years. Researchers credit conservation efforts made by hunters, as well as government funding for wetland protection and restoration.

The study also found that the bald eagle has made an amazing comeback since the 1970s, when the pesticide DDT was banned and endangered species legislation began offering protection to the birds.

"It's a wake-up call that we've lost more than a quarter of our birds in the U.S. and Canada," said coauthor Adam Smith from Environment and Climate Change Canada.

"But the crisis reaches far beyond our individual borders. Many of the birds that breed in Canadian backyards migrate through or spend the winter in the U.S. and places farther south — from Mexico and the Caribbean to Central and South America. What our birds need now is an historic, hemispheric effort that unites people and organizations with one common goal: bringing our birds back."