The Rusty Blackbird runs a close second to the Tricolored Blackbird in alarming population declines. Over the past 40 years, populations have declined by 85% to 95% across North America. Populations may be even lower; it’s an exceptionally difficult species to count.
The Rusty Blackbird breeds in the boreal forests of Alaska and Canada. It’s very strong associated with the wetlands, bogs, marshes and swamps of the taiga. With the exception of some areas in west-central Canada, the breeding grounds are largely intact, although the impact of climate change is an increasing concern. The wetlands exists because of underlying permafrost; as boreal forest temperatures rise, the permafrost melts and in some cases the wetlands disappear.
The problem seems to be in the wintering range, where habitat is being lost and poisoning efforts targeted at Red-winged, Brewer’s Blackbird and Grackles incidentally kill the far less common Rusty Blackbirds as well. Most researchers believe a combination of factors are contributing to the species’ population declines. Solutions are not obvious.
Rusty Blackbirds resemble their Brewer’s Blackbird cousins with the pale iris in the male and overall near-black coloration. But Rustys don’t have the purplish gloss of Brewers, and Rustys commonly have the brownish margins on their feathers that is one of the reasons for their common name. The other is the male Rusty Blackbird’s call, which “resembles rusty hinges and is ‘far from musical.'”
The female builds a fairly large, robust nest. The nests are durable and are used by other species in later years, including Solitary Sandpiper. The nest is almost always constructed near water. The female lays 3-5 eggs, which hatch after 10-12 days of incubation. Only the female broods the hatchlings, but both parents feed them. The kids fledge after 11-14 days, but remain with the adults for up to four weeks. At least at sites monitored in Alaska, the kids’ survival to immature birds is a very high 79%. Which points to the breeding range not being the problem.
In migration and on its wintering grounds, Rustys form mixed-species flocks and roost with starlings and other blackbirds. Those winter aggregations in the southern U.S. regularly exceed 1 million birds. The flocks have been subjected to lethal control to reduce nuisance, health and crop-damage problems. Rusty Blackbirds typically constitute less than 1% of those winter roosts, but get killed as well. It isn’t clear whether the killing of large flocks disproportionately affects the overall population of the Rusty Blackbirds. However, declines in Common Grackle populations in the eastern U.S. have coincided with roost control programs in the mid-1970s.
The species is hard to study on its breeding range. Traditional methods like Breeding Bird Surveys don’t effectively reach the overwhelming majority of the species breeding habitat. Rusty Blackbirds are presently classified as Vulnerable by the IUCN. But the species is headed for the Endangered Species list if the causes of the drastic population can’t be determined and addressed.