A study published in the journal Science found that North America has lost nearly 3 billion birds, or 29% of its avian population, since 1970.
That means more than one in four birds have disappeared from the landscape in the last 50 years, says the Audubon Society.
Usually, conservation experts focus on one specific species. But by tracking the broader avian population, researchers discovered the larger trend over time.
According to the Audubon Society, the research team analyzed the breeding population of 529 species by pooling data from the North American Breeding Bird Survey, Audubon’s Christmas Bird Count, U.S. Fish and Wildlife Service waterfowl surveys, and 10 other datasets.
The showed that birds breeding in at-risk habitats such as the Arctic tundra and grasslands are declining the drastically.
Kenneth Rosenberg, one of the lead researchers in the study, told the Audubon Society that there isn't one single factor that can account for this scale of loss.
Some potential reasons for the population decline are habitat loss, pesticide use, insect decline, and climate change. Overt threats like outdoor house cats and glass skyscrapers were also cited. For migratory species, long journeys and changes to winter habitats may be a compounding factors.
“My hope is that this will spawn a greater awareness that we really need to take care of our environment,” says one of the researchers in the study, Arvind Panjabi told the Audubon Society. “In order to prevent another third of our birds disappearing before too long, we need to change how we do things.”