Nearly one-third of the wild birds in the United States and Canada have vanished since 1970, a staggering loss that suggests the very fabric of North America’s ecosystem is unraveling.

The disappearance of 2.9 billion birds over the past nearly 50 years was reported today in the journal Science , a result of a comprehensive study by a team of scientists from seven research institutions in the United States and Canada.

As ornithologists and the directors of two major research institutes that directed this study, even we were shocked by the results. We knew of well-documented losses among shorebirds and songbirds. But the magnitude of losses among 300 bird species was much larger than we had expected and alarmingly widespread across the continent.

What makes this study particularly compelling is the trustworthiness of the data. Birds are the best-studied group of wildlife; their populations have been carefully monitored over decades by scientists and citizen scientists alike. And in recent years, scientists have been able to track the volume of nighttime bird migrations through a network of 143 high-resolution weather radars. This study pulls all of that data together, and the results signal an unfolding crisis. More than half our grassland birds have disappeared, 717 million in all. Forests have lost more than one billion birds.