A species of bird now flying north to summer breeding grounds in the boreal forests of Alaska and Canada has fallen on hard times, and biologists are asking the public to help figure out why.
The rusty blackbird population, once huge across North America, has decreased dramatically since 1966, with drops estimated to range between 85 and 99 percent. Total population figures are vague, 158,000 to 2 million, according to biologists. But the decline is unmistakable, and it has earned the bird a “vulnerable” listing from the International Union for the Conservation of Nature and a spot on Audubon Alaska’s Red List of troubled species.
The birds are known for their yellow eyes, the rust-colored tinges on their mostly dark feathers and the creaky noise that comes out of their beaks.
“They’re songbirds, but it’s not necessarily a pretty song. It sounds like a rusty hinge on a door,” said Beth Peluso, spokeswoman for Alaska Audubon.
Yet to be understood is the reason for the sharp decline in population, which appears to have been most precipitous in recent years — or even a good estimate of the population or the exact flight patterns and habits of the birds.
This is where the Rusty Blackbird Spring Migration Blitz comes in. The blitz, and its winter counterpart, is a campaign to enlist avid birders and other citizens in a U.S.-Canada rusty blackbird tracking project that gathers information to help scientists.
The blitz is led by the Rusty Blackbird Working Group, a panel of scientists that includes David Tessler, an Alaska Department of Fish and Game biologist who has extensively studied the bird species in Alaska, where much of the population stays during summer. Rusty blackbirds particularly favor boggy black spruce forests in interior and western Alaska.
The Alaska portion of the North American-wide blitz is being coordinated by the Department of Fish and Game and Audobon Alaska. They are appealing to Alaskans to watch for the birds’ arrival in Alaska through the end of May and report locations and any interesting behavior.
The big decline of the rusty blackbird population was first detailed in 1999, Tessler said. But no leading suspect has been fingered, he said.
“There’s no smoking gun right now,” he said.
Changing winter habitat
One possible cause is large-scale loss of winter habitat in the southeastern and south-central United States. Decades of development have transformed that area from hardwood forests to farms to suburbs. Even some seemingly incremental shifts, such as the move from pecan crops to soybeans, might have had a negative impact on rusty blackbird habitat, Tessler said.
Also possibly implicated is the recent change to boreal wetlands in Alaska and Canada that are favored by the rusty blackbirds. A warming climate has dried out the forests, possibly affecting the birds, Tessler said.
The rusty blackbirds might be having a harder time finding their favorite food, dragonfly larvae, Tessler said: “They’re really super-super-dependent on them,” he said. One recent study found that dragonfly larvae accounted for more than 90 percent of the food given to chicks in the Copper River Delta. It is possible, Tessler said, that climate change has disrupted timing, so that the larvae are not around when the birds arrive in their northern breeding grounds.
Industrial pollution in the U.S. northeast, where mercury contamination has been a problem, also might be implicated, he said.
Timber practices in the northeastern United States might be diminishing the habitat used by the wetlands-favoring birds, according to one hypothesis, he said.
And Lower 48 farmers’ longtime practice of killing rusty blackbirds, among other blackbirds, might still have an impact, Tessler said. For decades, the birds were considered agricultural pests, and “control” practices were authorized to get rid of them, he said. Though such bird kills are no longer allowed, they might be continuing illegally, though at lower levels, he said.
This year’s northward migration has been slowed by snow and cool weather in the southeastern part of the country. But as of Wednesday, there had been at least one sighting of a migrating rusty blackbird in Alaska. In addition, at least one bird was reported to have spent the winter in Delta Junction, Tessler said.
The Rusty Blackbird Spring Blitz is intended to be a three-year project. The working group also oversees a fall migration blitz.
Canada: Flame retardants found in Arctic gulls, Eye on the Arctic
United States: Shippers and seabirds clash over Arctic territory says study, Alaska Dispatch