Collapsing bird numbers in North America prompt fears of ecological crisis – research

Study using citizen data finds three-quarters of nearly 500 species in decline, with steepest trend in areas where they once thrived

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Bird populations across North America are falling most quickly in areas where they are most abundant, according to new research, prompting fears of ecological collapse in previously protected areas.

Analysis of nearly 500 bird species across North America has found that three-quarters are declining across their ranges, with two-thirds of the total shrinking significantly.

The study, published in the journal Science, indicates that former strongholds for bird species are no longer safe, particularly in grasslands, drylands and the Arctic.

In one of the most ambitious uses of citizen science data so far, scientists at the Cornell Lab of Ornithology used observations from eBird, a popular application used by birdwatchers to record sightings, to model changes between 2007 and 2021. The granularity of the data allowed researchers to track the rate of change in 27 sq km (10 sq miles) segments across North America, showing dramatic declines in areas where less than two decades ago bird species had thrived.

Williamson’s sapsucker is threatened in more than half of the states and provinces where it breeds, according to the report. Photograph: Blair Dudeck/Cornell Lab of Ornithology/Macaulay Library

“We’ve known for several years that a lot of bird species in North America have been declining. With this study, we were aiming to understand in much finer spatial resolution where birds were declining and where they might be increasing. Rather than having a range-wide trend to see if a species is going up or down, we want to know where it is going up and down,” said Alison Johnston, director of the Centre for Research into Ecological and Environmental Modelling at the University of St Andrews, UK, who led the study.

“The main ecological finding is that the locations where these species were thriving in the past, where the environments were really well suited to birds, are now the places where they are suffering the most,” she said.

The researchers said further studies were needed to explain the reasons behind the changes, many of which were dramatic, with populations falling by more than 10% a year in some areas. Global heating and habitat change were put forward as the main theories behind the shifts, but Johnston said they ultimately did not know.

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