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