Ever since blackbirds fell from the sky in Arkansas on New Year's Eve, the Cornell Lab has continued to receive numerous inquiries from the media and the concerned public about the significance of that event and other reports of dead birds at locations around the world. These isolated events, although dramatic, are not highly unusual in frequency or scale. Within the United States, for example, the USGS has recorded 188 events during the past 10 years involving more than 1,000 birds per incident--about 18 events per year on average, or more than one per month, attributed to disease and other causes.
"Although wildlife die-offs always pose a concern, they are not all that unusual," said Jonathan Sleeman, director of the USGS NWHC in Madison, Wis., which is completing its analyses of the Arkansas and Louisiana birds. "It's important to study and understand what happened in order to determine if we can prevent mortality events from happening again."
In 2010, the USGS NWHC documented eight die-off events of 1,000 or more birds. The causes: starvation, avian cholera, Newcastle disease and parasites, according to Sleeman. Such records show that, while the causes of death may vary, events like the red-winged blackbird die-off in Beebe, Ark., and the smaller one near Baton Rouge, La., are more common than people may realize.
Should we be worried about an "aflockalypse?" Yes, but not about the media coverage focusing on isolated events that affect only a few hundred or thousand birds at a time. It's the constant, chronic losses from habitat destruction and other causes that should truly concern us. Consider that 100 million birds are estimated to die from window collisions in the United States alone each year. That's more than 270,000 per day on average. Cats are estimated to kill another 100 million per year. And that's just the tip of the iceberg; habitat loss and degradation are the largest causes of massive declines in the numbers of birds.
Although we cannot witness these declines on a given day, citizen-science participants have contributed decades of data that point to truly alarming declines. Data from the Breeding Bird Survey show that Rusty Blackbirds, for example, have declined by 95% since the 1960s, indicating a loss of tens of millions of birds. Data from Project FeederWatch show that Evening Grosbeaks have also declined rangewide since the 1980s.