Canada warbler COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

Breeding range

The species is found in a variety of forest types, but is most common in wet, mixed deciduous-coniferous forest with a well-developed shrub layer (Conway 1999). It is often found in shrub marshes, red maple (Acer rubrum L.) stands, cedar stands, conifer swamps dominated by black spruce (Picea mariana) and larch and riparian woodlands along rivers and lakes (Peck and James 1987; Brauning 1992; Semenchuk 1992; Foss 1994; Larue et al. 1995; Cooper et al. 1997; Wildlife Resource Consulting Service MB Inc. and Silvitech Consulting 1997; Conway 1999; Drapeau et al. 2000; Manitoba Avian Research Committee 2003; Lambert and Faccio 2005; Chase 2005). It is also associated with ravines and steep brushy slopes near these habitats (Cooper et al. 1997; Lambert and Faccio 2005; South Peace Bird Atlas Society 2006).

In some parts of the range, the species will also breed in mature (>90 years) upland forests with canopy gaps that promote a dense, well-developed shrub layer (Schieck et al. 1995; Enns and Siddle 1996; Cooper et al. 1997; Hobson and Bayne 2000a; Hobson et al. 2000; Schieck and Hobson 2000; Schieck et al. 2000; Cumming and Machtans 2001; Machtans and Latour 2003; Hannon et al. 2004; Lambert and Faccio 2005; E. Bayne pers. comm. 2007; South Peace Bird Atlas Society 2006).  

Throughout its breeding range, the Canada Warbler can also be locally abundant in regenerating forests (i.e., 6–30 years post-disturbance) following natural (forest fires) or anthropogenic (harvesting) disturbances (Titterington et al. 1979; Wildlife Resource Consulting Service MB Inc. and Silvitech Consulting 1995; Christian et al. 1996; Hobson and Schieck 1999; Drapeau et al. 2000; Schieck and Hobson 2000; Hobson and Bayne 2000b; R. Berger pers. comm. 2006).

Spring and fall migration

During migration, the Canada Warbler is associated with habitats having a well-developed shrub layer, such as forest edges, riparian habitats, and second-growth forests (Conway 1999). In Central America, it uses the shrub layer and upper layers of humid to semi-humid forests and forest edges from sea level to 2,500 m (Binford 1989; Howell and Webb 1995). In Honduras and Panama, it occurs in open forests, second-growth forests, shrubland habitat and mangrove forests (Monroe 1968).

Winter range

In South America, the Canada Warbler uses mature rainforests and cloud rainforests at an altitude of 1,000–2,100 m, but may also use second-growth forests and forest edges (Ridgely and Tudor 1989; Curson et al. 1994). In Colombia, it occurs primarily in mountainous areas and foothills at 1,000–2,500 m (Hilty 1980). In Peru and Ecuador, the species uses rainforests on the east slope of the Andes and the adjacent lowlands (Paynter 1995). It also uses more open habitats, such as coffee plantations, agricultural field edges and semi-open areas (DeGraaf and Rappole 1995).

Habitat trends

Breeding range

Much of the forested wetlands in the eastern part of the species range have been drained (Tiner 1984; Conway 1999) and converted to agriculture or urban developments (Cadman et al. 1987; Gauthier and Aubry 1996). Regeneration of forest following clearing in the early to mid-1900s probably provided habitat for Canada Warblers. However, the continued maturation of the forest in those areas since that time has likely reduced the suitability of the habitat (Conway 1999).

In the western part of the range, boreal mixedwood forest has been converted to agriculture, potentially decreasing the amount of Canada Warbler habitat (Hobson et al. 2002). The annual rate of deforestation in the boreal forest transition zone of central Saskatchewan between 1966 and 1994 was 0.89%, three times higher than the global average (Hobson et al. 2002). Moreover, it is estimated that 7.3 million ha of boreal forest have already been converted for urban development and agriculture in Manitoba, Saskatchewan and Alberta (Senate Subcommittee on the Boreal Forest 1999).

Forests in western Canada are also believed to be in decline due to their permanent conversion by logging, road construction, oil and gas drilling and other industrial infrastructure (Senate Subcommittee on the Boreal Forest 1999; Schneider et al. 2003). According to the Senate Subcommittee on the Boreal Forest (1999), 70% of stands more than 90 years old in northwestern Canada have already been harvested and converted to plantations by forestry activities. Models developed to predict the cumulative impacts of current industrial development (including forestry, oil and gas development and other activities) planned in northeastern Alberta indicate that, at the current rate of development, old-growth stands of softwoods would be eliminated within 20 years and old-growth stands of hardwoods within 65 years (Schneider et al. 2003). Even under a management scenario involving the application of best practices, a major decline in old-growth stands is also predicted (Schneider et al. 2003).

Although the loss of old-growth forests may be offset by stand regeneration, post-treatment silvicultural practices that reduce the shrub layer could adversely affect the quality of Canada Warbler habitat in these areas (Gauthier and Aubry 1996). Further studies are therefore needed to assess the impact of silvicultural practices on the quantity and quality of managed forests for Canada Warbler in Canada.

Winter range

According to Davis et al. (1997), the forests of the northern Andes (i.e., primarily in Colombia), located between 500 and 2,000 m in altitude, the main winter grounds of the Canada Warbler (Conway 1999), are among the most threatened forests in the world. Approximately 90% of all primary forest in the northern Andes, including 95% of the cloud rainforest, has been deforested since the 1970s (Henderson et al. 1991). In Colombia alone, the rate of deforestation in the early 1990s is believed to have been between 1.5 and 2.2 million acres per year (World Press Review 1993) and only 5% of the primary forest of the western slope of the Andes remains (Dodson and Gentry 1991). Although no current data are available, it is highly likely that the area covered by primary forest has continued to decline since the 1990s. The same appears to be true for the cloud forests of Ecuador and northern Peru, although the habitat has been lost at a much slower rate (Terborgh 1989; Dillon 1994).

Habitat protection/ownership

In Canada, the breeding habitat of the Canada Warbler is generally on public lands, where the degree to which the habitat is protected is unknown. The species is, however, present in 21 of Canada’s national parks (P. Achuff pers. comm. 2006) and in several other protected sites under provincial jurisdiction. The total area of these protected sites accounts for less than 10% of Canada’s total area (Senate Subcommittee on the Boreal Forest 1999) and is likely a small proportion of the species’ breeding range. Notable examples of protected sites in boreal areas where Canada Warblers breed include: Wood Buffalo National Park (35,437 km²) in Alberta, Prince Albert National Park (3,874 km²) and Lac La Ronge Provincial Park (3,362 km²) in Saskatchewan, Wapusk National Park (11,475 km²) and Riding Mountain National Park (2,973 km²) in Manitoba, Wabakimi Provincial Park (8,711 km²), Woodland Caribou Provincial Park (4,795 km²) and Georgian Bay Islands National Park (13 km²) in Ontario and La Mauricie National Park (540 km²) in Quebec and Prince Edward Island National Park (22 km²) in Prince Edward Island.  

The vast majority of Crown forests have been allocated to the forest industry for timber and pulp production. Most provinces have adopted forest management practices that might help to reduce the impact of forestry on Canada Warbler habitat (e.g., riparian woodland protection programs; Biodiversity Field Guide of the Forest Practices Code of British Columbia Act; Cooper et al. 1997). In addition, a number of forest certification systems have been adopted by various forest companies and implemented on over 15 million ha in several sectors of Canada’s boreal forests (Forest Stewardship Council 2006).

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