A team of researchers from universities, government agencies, and nonprofit organizations collaborated on a new study to track bird populations on the North American continent. What they found was alarming. According to their analysis, there are 29 percent fewer birds in the United States and Canada today than there was in 1970, a decline of nearly 3 billion birds. The analysis was recently published in the journal Science
The study’s authors, who include scientists from Canada’s environment agency and the U.S. Geological Survey, undertook what is the largest effort yet to document bird decline. Birds are probably the best-monitored animals on Earth. For decades, an army of devoted amateur bird-watchers have helped professional ornithologists by submitting their observations to databases and carrying out annual surveys of bird populations.
The researchers used this wealth of data to compile their analysis of the populations of 529 bird species since 1970, the earliest year for which there is solid data. They were able to analyze data for 76 percent of all bird species in the United States and Canada, which represents almost the entire population of birds. This data was then cross-referenced with data from springtime scans from 143 weather radars, which can detect birds migrating in great numbers. The data from the weather radars was consistent with the drop recorded in the bird-watching records.
The analysis revealed ‘tremendous losses’ across diverse groups of birds and habitats. Of the nearly three billion birds lost, 90 percent belonged to 12 bird families. Grassland species suffered the biggest declines, having lost 717 million birds. There are 440 million fewer blackbirds and 83 million fewer starlings. David Yarnold, president and chief executive of the National Audubon Society, called the findings “a full-blown crisis.”
Several threats could be responsible for the large-scale bird decline. Agricultural activities have destroyed habitats and spread pesticides that kill the insects many birds eat. Roaming cats light pollution, and structural obstructions, like buildings, are also considered to be factors. Climate change is expected to become a more prominent factor over time by further altering habitats and threatening the plant communities on which birds rely.