Calling it an “overlooked biodiversity crisis,” researchers say that the United States and Canada have lost nearly 3 billion birds in the last 50 years, according to the Washington Post.
The loss means there are 29% fewer birds in the two countries compared to 1970, the Post reported.
According to the reports, 90% of the bird loss is among a dozen bird families, which includes sparrows, warblers, blackbirds and finches, according to NPR. The number of grassland birds has decreased by 53%, and shoreline birds have decreased by a third.
What has led to such dramatic losses? There are likely several factors, according to researchers.
Grassland bird species have likely been affected by agriculture, particularly pesticides that kill off insects the birds eat, according to the Post. Habitat loss has also played a large part.
“Every field that’s plowed under, and every wetland area that’s drained, you lose the birds in that area,” Kenneth V. Rosenberg, lead author of the bird loss study and a conservation scientist at Cornell University and the American Bird Conservancy, told the New York Times.
Previous studies have noted other threats to birds, including light pollution, tall buildings and predators like cats, according to the Post.
What sort of impact does the loss of birds have on the environment? According to researchers, it may be a sign of a larger problem.
Birds play an important role in ecosystems. “Declines in your common sparrow or other little brown bird may not receive the same attention as historic losses of bald eagles or sandhill cranes, but they are going to have much more of an impact,” Hillary Young, a conservation biologist at the University of California, Santa Barbara, told the Times.
Different types of birds take on different roles in an ecosystem, the report in the Post explains. Some birds disperse seeds, leading to pollination and plant growth. Other birds are predators that help control pest populations.
“They’re integral to the system,” Mike Parr, co-author of the study and president of the American Bird Conservancy, told the Post. “It’s like a very large corporation in a marketplace — they’re diversified across all areas. If that corporation starts to have problems, then it starts showing up everywhere.”
But not all of the study’s findings were negative. Researchers found that some bird populations are increasing, including raptors, such as bald eagles, and wetland birds like ducks and geese, the Post said.
In the case of these birds, their increase is due to conservation efforts and protections they received, authors of the study told the Post. It also shows that these efforts can work.
“In those cases, we knew what the causes were and we acted on that,” Rosenberg told the Times. “They’re models of success.”