Over the past half-century, North America has lost more than a quarter of its entire bird population, or around 3 billion birds.
"We saw this great net loss across the entire bird community," says Ken Rosenberg, a scientist in Ithaca, N.Y. "But we also knew that other bird populations were increasing. And what we didn't know is whether there was a net change."
Common birds with decreasing populations include dark-eyed juncos and red-winged blackbirds, says Rosenberg. Grassland birds have suffered a 53% decrease, and more than a third of the shorebird population has been lost. Bird populations that have increased include raptors (猛禽), like the bald eagle, and waterfowl.
"The numbers of ducks and geese are larger than they've ever been, and that's not an accident," says Rosenberg. It's because hunters who mainly want to see healthy waterfowl populations for sportful hunting have raised their voices.
"People are doing a wonderful effort to try and understand our bird populations with a lot of uncertainty, but the actual systems that we have in place to try and answer really tough questions like this are really far short of what we need," Ted Simons in North Carolina State University says.
"In all, the conclusions weren't necessarily surprising," says Kristen Ruegg, a biologist at Colorado State University. There have been hints (暗示) that the loss was this large from all kinds of sources over the past few years. But in most cases, these were species-specific records of local extinctions or models of projected losses, resulting from things like climate change. This really sort of wakes people up to the idea that this is happening.
Elise Zipkin, a quantitative ecologist at Michigan State University, says the loss can be a big problem. "Just because a species hasn't gone extinct (灭绝) or isn't even necessarily close to extinction, it might still be in trouble," she says. We need to be thinking about conservation (保护) efforts for that."
