Rusty blackbird (Euphagus carolinus) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Wintering habitat

On its migration routes and wintering grounds, the Rusty Blackbird is generally associated with wetlands, such as flooded forests, scrub along the edges of lakes, rivers and streams and beaver ponds (Avery 1995; Cyr and Larivée 1995; Campbell et al. 1997). It also occurs to a lesser degree in human-made habitats, such as pastures, plowed fields, sewage treatment ponds, and small landfill sites (Avery 1995; Campbell et al. 1997; Sinclair et al. 2003).

Breeding habitat

The breeding range of the Rusty Blackbird corresponds closely to the boreal forest and taiga terrestrial ecozones (Godfrey 1986; Cadman et al. 1987; Erskine 1992; Semenchuk 1992; Avery 1995; Gauthier and Aubry 1995; Campbell et al. 1997; Sinclair et al. 2003). Within these biomes, Rusty Blackbird habitat is generally characterized by conifer forest wetlands (Erskine 1977; Gunn et al. 1977; DesGranges and Houde 1989; Gauthier and Aubry 1995). The Rusty Blackbird is generally absent from wetlands in regions above the tree line, such as the alpine tundra and Arctic tundra, and it is not abundant in high mountain wetlands (DesGranges and Houde 1989; Campbell et al. 1997).

In forested areas, the Rusty Blackbird is strictly riparian and rarely uses the forest interior (Whitaker and Montevecchi 1999). It occurs primarily in wetlands associated with recent burns, wooded heathland, and peat bogs with or without ponds, as well as in riparian scrub, open moss- and lichen-spruce woodlands, and areas dominated by conifer forest edges and lakes and bogs (Consortium Gauthier et Guillemet – G.R.E.B.E. 1991, 1992; Avery 1995). The Rusty Blackbird also occurs in sedge meadows, marshes, muskegs, swamps and estuaries (Schweinsburg 1974; Erskine 1977; Gunn et al. 1975, 1977; Spindler and Kessel 1980; DesGranges and Houde 1989; Semenchuk 1992; Avery 1995; Gauthier and Aubry 1995; Campbell et al. 1997; Sinclair et al. 2003). In eastern Canada, the Rusty Blackbird uses scrub riparian habitats of islands, lakes, rivers and streams as well as alder and willow thickets (Darveau et al. 1995; Larue et al. 1995; Whitaker and Montevecchi 1999). In the southeastern portion of its breeding range, the Rusty Blackbird’s habitat is reportedly also associated with natural disturbances that favour early successional habitats, such as fire, windthrow and wetlands created by beavers (Castor canadensis; Ellison 1990). In Nova Scotia, and more specifically Cape Breton, it also occurs in drier environments, such as pasture (Erskine 1992).

Habitat trends

Wintering habitat

A large portion of the Rusty Blackbird's winter range includes the flood plains of the Mississippi Valley from southern Illinois to the Louisiana coast (Avery 1995). The conversion of the wetland forests in these areas for agriculture and urban development is considered one of the most significant factors in the decline of the Rusty Blackbird (Greenberg and Droege 1999). This forest massif, with an area of 97,124 km² has decreased in size by 80% over the last 150 years, and now consists of 20,234 km² of detached forest tracts (Hefner and Brown 1984). Between 1950 and 1980, alone, more than 25% of flood plain forests along the Mississippi were converted (Hefner and Brown 1984).

Breeding habitat

In Canada, Rusty Blackbird breeding habitat, particularly in the southern part of the species’ breeding range, has been lost with the conversion of wetlands to agriculture and urban development (Hobson et al. 2002).

Current habitat is also potentially affected by several other factors. For example, the flooding of vast areas of land to create hydroelectric reservoirs could have adverse effects on Rusty Blackbird habitat. In northern Québec and Newfoundland and Labrador, the creation of reservoirs currently affects 1.5% of the boreal forest and that figure is expected to increase in the coming decades (Hayeur 2001). Although the creation of new wetlands under mitigation programs compensates to some extent for wetland loss caused by the creation of reservoirs (Hayeur 2001), the quality of the new habitat for the Rusty Blackbird is not yet known.

Rusty Blackbird habitat may also be affected by drainage and pumping activities associated with oil and gas extraction, which remove large volumes of freshwater from underground and surface reserves (Griffiths and Woynillowicz 2003). The demand for water resources by the Alberta oil and gas industry for oil sands extraction activities is expected to increase by a factor of three by 2020 (Griffiths and Woynillowicz 2003).

Finally, rising temperatures caused by climate change could affect northern wetlands by melting permafrost and drying peatlands (Natural Resources Canada 2004).

A rough estimate of Rusty Blackbird habitat conversion in Canada’s boreal forest suggests that the area rendered non-viable for this species is around 5%. With the increase in industrial development that is anticipated in the medium term (i.e., in the next 50 years) there is a predicted additional conversion of 4% of Rusty Blackbird breeding habitat (based on data from: Global Forest Watch Canada 2000; Hayeur 2001; Griffiths and Woynillowicz 2003; Kling et al. 2003; Wildlife Habitat Canada 2003).

Habitat protection/ownership

In Canada, approximately 94% of Rusty Blackbird habitat is located on public lands (Global Forest Watch Canada 2000). Only 9% of the boreal forests and wetlands in northern ecozones is protected; an area equivalent to approximately 125,000 km² (Wildlife Habitat Canada 2003; Table 1). The percentage of wetlands protected in each ecozone ranges from 14.4% in the Hudson Plains ecozone to 5.3% in the Atlantic Maritime ecozone (Table 1).

 

Table 1. Total protected area of potential Rusty Blackbird habitat, by ecozone, within its Canadian breeding range (based on Wildlife Habitat Canada 2003). Protected areas include all IUCN Protected Area Management categories such as: Strict nature reserve/wilderness protection areas; Wilderness areas; National parks; Natural monuments; Habitat/Species Management Areas; Protected Landscape/Seascape and Managed Resource Protected Areas.
Ecozones Total area
(km²)
Area protected
(km²)
Percentage protected per ecozone
Hudson Plains 295,349 42,395 14.4
Taiga Plains 231,119 16,525 7.2
Taiga Shield 166,487 10,022 6.0
Taiga Cordillera 21,142 1,361 6.4
Boreal Plains 309,644 31,477 10.2
Boreal Shield 333,658 19,276 5.7
Boreal Cordillera 15,732 1,143 7.3
Montane Cordillera 28,441 1,582 5.6
Atlantic Maritime 17,558 924 5.3
Total 1,419,130 124,705 8.8

In the wintering range, protected sites with significant amounts of Rusty Blackbird habitat are mainly located in the Mississippi Valley, notably in the Cache River National Wildlife Refuge in Arkansas (223 km²), the largest remaining area of intact flood plain forest alongside the Mississippi, and the Pearl River Wildlife Management Area in Louisiana (142 km²).

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