North America's Bird Populations Are Shrinking Faster. Blame Climate Change and Agriculture

"Billions fewer birds are flying through North American skies than decades ago," reports the Associated Press, "and their population is shrinking ever 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 Thursday's journal Science... 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... 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," [said study co-author Marta Jarzyna, an ecologist at Ohio State University]. "On the other hand, the acceleration of those declines, that's mostly driven by agricultural practices." The scientists found statistical correlations between speeded-up decline rates and high fertilizer use, high pesticide use and amount of cropland, Leroy said. He said they couldn't say any of those caused the acceleration of losses, but it indicates agriculture in general is a factor. "The stronger the agriculture, the faster we will lose birds," said Leroy... McGill University wildlife biologist David Bird, who wasn't part of the study, said it was done well and that its conclusions made sense. With a growing human population, agriculture practices are intensified, more bird habitats are being converted to cropland, modern machinery often grind up nests and eggs and single crop plantings offer less possibilities for birds to find food and nests, said Bird, the editor of Birds of Canada. "The biggest impact of agricultural intensity though is our war on insects. Numerous recent studies have shown that insect populations in many places throughout the world, including the U.S., have crashed by well over 40 percent," Bird said in an email. "Many of the birds in this new study showing population declines depend heavily on insects for food." A 2019 study of the same bird species by Cornell University conservation scientist Kenneth Rosenberg also found that North America had 3 billion fewer birds than in 1970, the article points out.

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