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In the late 1800s and early 1900s, naturalists across much of North America described immense flocks of migrating rusty blackbirds that, in the words of one, “blacken the fields and cloud the air.” But by the mid-1990s, when Russell Greenberg, head of the Smithsonian Migratory Bird Center, spent two summers doing boreal songbird field research in northern Canada, there was hardly a rusty blackbird to be found.
His interest piqued, Greenberg, with the help of a friend, began looking at Breeding Bird Survey, Christmas Bird Count, and other data, only to make the alarming discovery that this wooded-wetlands species was in serious trouble. As it turns out, rusty blackbird populations have plummeted a staggering 88 percent or more since the mid-1960s, probably the sharpest decline of any North American land bird. Population estimates vary widely, from 158,000 to 2 million individuals. “It’s not someplace like Brazil or Guyana,” Greenberg says. “This bird is slipping away right here.”
To get to the bottom of the mysterious decline, Greenberg and a dozen or so colleagues formed the International Rusty Blackbird Technical Working Group in 2005. Since then more than 60 members have filled in gaps in basic information about the birds, including diet (both plants and insects) and clutch size (five, on average). Amateur birders have also pitched in as well, to census the species’ winter range in the bottomland hardwood forests of the U.S. Southeast.
The scientists have found that habitat loss and degradation, along with mercury contamination, evaporation of wetlands in the bird’s boreal breeding range resulting from global warming, and blackbird control programs may all have contributed to the species’ decline. Still, without conclusive evidence, it’s hard to know what specific management recommendations will most likely be effective. “We essentially have this dying patient, and we don’t know what to do to help them,” says Dean Demarest, deputy regional chief for the U.S. Fish and Wildlife Service’s migratory bird program. “About all we can say is protect the boreal, protect the winter range, and we’ll get back to you.”
Scientists nonetheless remain hopeful that the work they’ve done with the species has helped to at least slow the decline. Greenberg says bird lovers can help the species by planting pecan trees (a favorite rusty blackbird food), supporting wetlands conservation, and entering their sightings into the eBird database.