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The Rusty Blackbird, until recently the least well known of North America’s blackbirds, breeds north to the tree line in wet forests of Alaska, Canada, and the northeastern United States. No other North American blackbird breeds as far north. Although detailed studies of its breeding biology have been few, this species nests most frequently along bogs, muskeg swamps, beaver (Castor canadensis) ponds, and streams, and its robust, arboreal nests are often reused by other species such as the Solitary Sandpiper (Tringa solitaria).
This blackbird is not distinctively marked except for brown, rust-colored edgings on its upperbody feathers in fall and winter. An opportunistic feeder, it eats mostly invertebrates during the breeding season, generally taking them by probing in mud and vegetation along the edges of wetlands. In winter and on migration, it joins mixed-species roosts and feeding flocks, but also occurs apart from other species, favoring woodlands more than other blackbirds do. Also unlike other blackbirds, the Rusty is seldom a nuisance depredating crops or at roosts.
Rusty Blackbirds have declined alarmingly (85-95%) in numbers over the past 40 years (1970-2010), spawning a recent spurt in studies of this species (Greenberg and Matsuoka 2010). Potential factors promoting this decline have been identified and include loss of wetlands used by wintering individuals in the Southeast, contaminants on breeding grounds, poisoning of other blackbirds on wintering roosts (with the Rusty as an incidental victim), and increasing disturbance of boreal wetlands where this species breeds. Alone, none of these factors appears adequate to account for the broad and extraordinary loss in numbers of this species, so it is likely we are witnessing synergistic effects. Continued work is clearly needed to track population levels of this species and to better identify factors that may drive continued loss or recovery.