Shrinking North American bird population is getting worse faster. Experts blame agriculture, warming

Billions fewer birds are flying through North American skies than decades ago, and their population is shrinking faster, mostly due to a combination of intensive agriculture and warming temperatures, a new study found. Nearly half of the 261 species studied showed big enough losses in numbers to be statistically significant, and more than half of those declining are seeing their losses accelerate since 1987, according to the journal Science. The study is the first to look at more than the total bird population by examining the trends in their decrease, where they are shrinking the most, and what the declines are connected to. “Not only are we losing birds. We are losing them faster and faster from year to year,” said study co-author Marta Jarzyna, an ecologist at Ohio State University. The only consolation is that the birds that are shrinking in numbers the fastest are species—such as the European starling, American crow, grackle, and house sparrow—with large enough populations that they aren't yet at risk of going extinct, said study lead author Francois Leroy, also an Ohio State ecologist. Cornell University conservation scientist Kenneth Rosenberg, who wasn't part of the study, said the species declining fastest in the new research “are often considered pests or ‘trash birds,’ but if our environment cannot support healthy populations of these extreme generalists and extremely adaptable species that are tolerant of humans, then that is a very strong indicator that the environment is also toxic to humans and all other life.” The biggest locations for acceleration of bird loss were in the Mid-Atlantic, the Midwest, and California, the study found. And geography proved important when Leroy and Jarzyna looked for reasons why so many bird species are shrinking ever faster. When it came to population declines—not the acceleration—the scientists noticed bigger losses further south. When they did a deeper analysis, they statistically connected those losses to warmer temperatures from human-caused climate change. “In regions where temperatures increase the most, we are seeing strongest declines in populations,” Jarzyna said. “On the other hand, the acceleration of those declines, that’s mostly driven by agricultural practices.” This article was provided by The Associated Press.