According to a new study that brings together information on 529 bird species since 1970, North America has lost over 25 percent of its entire bird population over the past 50 years. That’s about 3 billion birds.
“We saw this tremendous net loss across the entire bird community,” said Ken Rosenberg, the study’s lead author and an applied conservation scientist at the Cornell Lab of Ornithology and the nonprofit American Bird Conservancy. “By our estimates, it’s a 30 percent loss in the total number of breeding birds.”
Rosenberg and his colleagues knew that some bird populations have been decreasing, but also that others were increasing, and began their research to determine whether there was a net change or shift in the total bird population.
To do this, they used data from surveys taken by volunteer bird spotters, such as the North American Bird Survey and the Audubon Christmas Bird Count. Once a year, thousands of volunteers counted all the birds they saw and heard in a short time period at locations along designated routes.
The researchers also used data on migration patterns taken from 143 weather radar installations over the past decade. The survey and radar data “measure different things, but they come to the same conclusion,” said study co-author Adriaan Dokter, a migration ecologist at the Cornell Lab of Ornithology.
90 percent of the decline is due to just 12 bird families, including sparrows, warblers, blackbirds and finches. Grassland birds are at a 53 percent decrease, and over 33 percent of shorebirds were lost as well.
Researchers have been expecting a loss of this size for the past few decades, largely in the form of species-specific extinction projections due to climate change. The newest study cites habitat degradation, urbanization and toxic pesticides as the primary potential causes for population loss. The intensification of agriculture in grassland areas, a population of birds that has been hit the hardest, is an example of this.
“Just because a species hasn’t gone extinct or isn’t even necessarily close to extinction, it might still be in trouble,” said Elise Zipkin, a quantitative ecologist at Michigan State University. “We need to be thinking about conservation efforts for that.”
Rosenberg pointed out that the bird populations that are notably increasing, such as waterfowl, are able to do so because of the efforts made by hunters.
“It’s because of the strong constituency of recreational waterfowl hunters who raised their voice, put money where their mouths are and saw to it that conservation programs and policies were put in place,” said Rosenberg. “Billions of dollars [were] invested into wetlands [and] into wildlife refuges. The North American Wetlands Conservation Act was enacted in the late 1980s. All of these things were responsible for the turnaround.”
Now is the time for everyone to be rethinking how their contributions can affect bird populations and their declines. Some have called for a tax on hiking or bird-watching equipment to support conservation programs, as well as other conservation models based on the successful waterfowl programs.