Researchers at Cornell University have uncovered a head-scratching statistic: bird populations are declining most severely in the areas they used to be thriving.
In a study published in the journal Science, researchers looked at the populations of 495 bird species across North America from 2007 to 2021. Of those species, 83 per cent are losing a larger percentage of their population in areas where they’re most abundant. The changes have been as drastic as 10 per cent declines in a year in some areas. Bird species in grasslands and the Arctic tundra are showing particularly steep declines.
“We’re not just seeing small shifts happening, we’re documenting populations declining where they were once really abundant. Locations that once provided ideal habitat and climate for these species are no longer suitable. I think this is indicative of more major shifts happening for the nature that’s around us,” said Alison Johnston, the lead author and director of the Centre for Research into Ecological and Environmental Modelling at the University of St. Andrews, U.K., in a statement.
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A 2019 study revealed that nearly three billion birds had been lost since 1970 with declines in every biome. The goal of the new study was to take a closer look at population trends in specific areas to help guide conservation efforts. “The 2019 paper was telling us that we have an emergency, and now with this work we have the information needed to create an emergency response plan,” said Johnston.
The study wasn’t all bad news, though. Researchers also found that 97 per cent of bird species analyzed saw their populations increase in some areas. This included spaces such as the Appalachian Mountains where the bird species hadn’t previously been abundant.
“Areas where species are increasing where they’re at low abundance may be places where conservation has been successful and populations are recovering, or they may point to locations where there may be potential for recovery,” said Johnston.
Further study will be required to figure out what factors are causing the population increases and decreases in specific areas. But thanks to advances in citizen science and technology, this kind of broadscale research could be possible.
As part of this study, the researchers analyzed 36 million citizen science observations shared on the birdwatching app eBird. To ensure the eBird data was reliable, the researchers used machine learning and statistical methodologies to run more than half a million simulations, requiring more than 6 million hours of computing—85 years of work on a standard laptop.
This was done alongside high-resolution satellite imagery that captured 27 square kilometre segments (approximately the size of New York City) across North America, helping the researchers track the rate of change. These were the smallest parcels of land ever analyzed in a continental-wide monitoring program. Previously, monitoring programs on this scale could only estimate population size for larger areas such as provinces and states.
“It’s this kind of small-scale information across broad geographies that has been lacking and it’s exactly what we need to make smart conservation decisions,” said Amanda Rodewald, a co-author on the study and the faculty director of the Center for Avian Population Studies at the Cornell Lab of Ornithology, in a statement. “These data products give us a new lens to detect and diagnose population declines and to respond to them in a way that’s strategic, precise, and flexible. That’s a game changer for conservation.”
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