Euphagus carolinus

Two subspecies are recognized in North America: Euphagus carolinus carolinus, which occupies most of the species' range, and the darker E. c. nigrans, which breeds in Newfoundland, Nova Scotia, Magdalen Island, and possibly eastern New Brunswick (AOU 1957, Avery 1995).

Few comprehensive molecular or morphological studies have been conducted on relationships between rusty blackbirds and other members of the sizeable family Icteridae. Brewer's blackbird (Euphagus cyanocephalus) is likely the closest relative. Species in the genus Euphagus are probably more closely allied with the grackles (Quiscalus) than to Agelaius blackbirds (Avery 1995).

The reasons behind current trends are poorly understood but several threats are suspected to be causing the declines. The destruction and conversion of boreal wetlands (predominantly in the southern boreal forests) is a significant threat to the species. Strip-mining for tar sands is expected to increase in the future, with up to 300,000 ha of Canada's boreal forest and wetland predicted to be directly affected over the next 30 to 50 years (Wellsÿet al.ÿ2008). Other possible threats include boreal wetland drying and chemical change resulting from global climate change, depletion of available calcium resulting from acid precipitation, increase in methyl mercury, loss of wooded wetlands in the south-east U.S. winter range, and mortality associated with past and ongoing blackbird control efforts. (Birdlife International, 2014).

Breeding range extends from western and north-central Alaska to southern Keewatin and Labrador, south to central British Columbia, central Saskatchewan, northern shores of Lake Superior and Lake Huron, southeastern Ontario, Vermont, New Hampshire, Maine, northeastern New York, Massachusetts, and Nova Scotia (Avery 1995). During the nonbreeding season, this species ranges from southcoastal Alaska, southern Canada, and northern United States south to Texas, Gulf Coast, and northern Florida (but primarily in the southeastern United States) (Avery 1995).

With a population estimate of over 5 million (Partners in Flight, 2013) and a distribution across all of northern Canada (Birdlife International, 2014), ther are undoubtedly at least 81 element occurrences for this species. But this species is classifed as vulnerable by Birdlife International

On wintering grounds, potential threats and/or causes for observed population decline include destruction of wooded wetlands and blackbird control programs; on breeding grounds, acid precipitation and conversion of boreal forest wetlands have been implied (Greenberg and Droege 1999).

Habitat degradation: Land-use practices that degrade or reduce wooded wetlands are detrimental to this species' habitat needs (Avery 1995). Greatest loss of wooded wetlands is on the wintering grounds. Between the mid-1950s and mid-1980s, about 25% of remaining wooded wetlands in the southeastern U.S, an area that encompasses most of the species' winter range, were drained and converted (Hefner and Brown 1984, Greenberg and Droege 1999). However, modern rates of wooded wetland conversion may not be sufficient to explain the severity of recent declines; changes on the breeding grounds may also be limiting this species (Greenberg and Droege 1999). Several other species that utilize high-latitude wetland habitats for breeding, such as the Horned Grebe (Podiceps auritius) and Lesser Yellowlegs (Tringa flavipes), are also experiencing survey-wide (BBS) declines (Sauer et al. 2005).

Clearcut logging on breeding grounds removes habitat and may also encourage establishment of competitors Common Grackles and Red-winged Blackbirds (Agelaius phoeniceus) (Ellison 1990), or encourage invasion by Brown-headed Cowbirds (Molothrus ater), a common and potentially problematic nest parasite (Avery 1995). Conversely, recently logged habitat, when saturated with water, may provide breeding habitat for this species; Ellison (1990) found several Rusty Blackbird nests and fledglings in recent clearcuts in Vermont. Although recent clearcuts may satisfy habitat requirements for this species, no data exists on the relative quality of these sites (Hannah 2000, 2004).

Blackbird control programs: Rusty Blackbirds may form mixed-species flocks in winter with other blackbirds and starlings, regularly exceeding 1 million birds. As a result, species has been subjected to lethal control to reduce nuisance, health, and crop damage problems (Avery 1995). Winter roost control programs in the eastern U.S. coincided with declines in Common Grackle populations (Avery 1995, Greenberg and Droege 1999). The overall effect on Rusty Blackbird populations is unknown but suspected localized and nominal, as this species typically constitutes <1% of winter roosts (Avery 1995).

Wetland acidification: Acidification of boreal wetlands due to industrial emissions is also of concern, particularly in eastern North America, but overall effects are unknown (Greenberg and Droege 1999). Since Rusty Blackbirds inhabit areas with naturally high soil acidity, it is difficult to determine the real impact of acidification (Darveau et al. 1989, Savignac 2004). Declines in snail abundance in acidified soils in the Netherlands have been linked to declines in passerine production (Graveland et al. 1994); given the high proportion of snails and mollusks in Rusty Blackbird diets, the impacts of acidification on food resources could be of concern (Greenberg and Droege 1999).