North America lost 29 percent of its bird populaiton—around three billion birds—over the last 49 years, according to a new report. 

“Decline of the North American avifauna,” a study released on Thursday in the journal Science, found that the continent has seen a net loss of 2.9 billion birds since 1970. 

“The birds are the canary in the coal mine,” The Bird Conservancy of the Rockies’ Arvind Panjabi, a study author, told Gizmodo. “When the birds are dying, it surely can’t be good for us either.”

Researchers found that “90% of the loss can be attributed to just a dozen bird families, including sparrows, warblers, blackbirds, and finches,” according to NPR. 

The report is a dire warning, said Cornell University’s Kenneth V. Rosenberg, the study’s lead author. 

“We were stunned by the result,” Rosenberg told The New York Times. “It’s just staggering.”