Kirtland's warbler (Dendroica kirtlandii) COSEWIC assessment and status report: chapter 5

Habitat

Habitat requirements

The Kirtland’s Warbler is a habitat specialist, occurring exclusively in early successional jack pine stands. These stands may have regenerated after wildfire or timber harvest (naturally regenerated or planted). However, today most Kirtland’s Warblers breed in jack pine plantations specifically managed for the species (Environment Canada 2006).

The species also appears to be area-sensitive. Mayfield (1992) found that they did not breed in tracts of jack pine smaller than 30 ha and that breeding success was higher in patches > 200 ha. Further support for the area sensitivity of the species comes from Anderson and Storer’s (1976) study, which demonstrated that 90% of nests that fledged Kirtland’s Warblers were from stands greater than 80 ha in area.

Kirtland’s Warblers also have specialized local habitat requirements. Dense stands of jack pine with ≥ 3,500 stems/ha, 35-65% canopy cover and high foliage volume are preferred (Probst 1988; Kepler et al. 1996). Stands are first colonized by Kirtland’s Warblers about six years following a fire, in areas where regenerating vegetation is most dense and 1.5-2.0 m in height (Mayfield 1992). Nesting success is highest in dense patches of pine trees, which are scattered in clumps and are 1.5-5 m tall (7-20 years old).

Although the species formerly bred only in early successional, fire-regenerated jack pine stands, more than 90% of the population now breeds in jack pine plantations specifically created for the species (Environment Canada 2006). In these plantations, trees are planted at 1.2 m intervals with 1.8 m between rows (4,510 trees/ha). Large elliptical spaces are integrated into the plantations to resemble openings in natural jack pine barrens and 25% of the plantation is left unplanted (Houseman and Anderson 2002). Kirtland’s Warblers will also breed in mixed plantations and sometimes in red pine (P. resinosa) or even Scots pine (P. sylvestris) plantations (Weinrich 1994).

Probst et al. (2003) suggested that based on historical breeding densities (Probst and Weinrich 1993), 200-400 ha of densely stocked jack pine would be needed on an ongoing basis to support 25 pairs of Kirtland’s Warblers. Were warblers to occupy a habitat patch for 10 years and assuming a 50-year rotation, 1,000-2,000 ha would be required to maintain sufficient jack pine regeneration for 25 pairs.

Kirtland’s Warblers nest on the ground on well-drained, sandy soils and typically with the following species: low-bush blueberry (Vaccinium corymbosum) and velvet-leafed blueberry (V. myrtilloides), bearberry (Arctostaphylos uva-ursi), bracken fern (Pteridium aquilinum), serviceberry (Amelanchier spp.), sand cherry (Prunus pumila), sweet fern (Comptonia peregrina), grasses (e.g., Andropogon spp.), sedges (Carex spp.) and goldenrods (Solidago spp.). Delaying planting for three years following a prescribed burn increased cover of low-bush blueberry – which appears to be an important species associated with warbler breeding (Houseman and Anderson 2002).

More details of habitat requirements are in Wood 1904; Barrows 1921; Leopold 1924; Wing 1933; Mayfield 1953, 1960, 1962; Line 1964; Anderson and Storer 1976; Chamberlain 1978; Buech 1980; Harwood 1981; Ryel 1981; Wright and Bailey 1982; Probst 1986; Probst and Hayes 1987; Probst and Donnerwright 2003; Probst et al. 2003.

Habitat trends

It is hard to determine habitat trends for the Kirtland’s Warbler because unless specific management is undertaken, preferred habitat is continuously changing as stands mature. Because no net gain in habitat was projected in the Lower Peninsula of Michigan for the early part of the 21st century, it was predicted that the Kirtland’s Warbler population would stabilize in this area (Probst and Weinrich 1993). In the Upper Peninsula, the successional stage of the four areas will soon render them unsuitable for Kirtland’s Warblers (tree heights 1.7-5.0 m). However, regenerating jack pine in other areas may compensate for this loss (e.g., in 1998-2000, Baraga Plains, north-east Delta County, and Schoolcraft County provided habitat).

No information is available on habitat trends for Kirtland’s Warbler in Canada. However, surveys show that some areas of jack pine in Ontario (e.g., Thessalon, Chapleau, Petawawa) have similar habitat structure and plant species composition to habitats occupied by Kirtland’s Warblers in Michigan (Bloom 2003), so suitable habitat may not be limited. Indeed, the Recovery Team, using Ontario Ministry of Natural Resources Forest Resource Inventory mapping, has identified extensive areas of apparently suitable jack pine habitat across central Ontario from Sault St. Marie/Chapleau to North Bay/Petawawa.

Details of differences between management practices in jack pine stands in Michigan managed specifically for Kirtland’s Warblers and typical management in jack pine stands in Ontario are provided in Table 1.

A recent theoretical study suggests that the range of the species may be extended northwards as habitat changes in response to warming trends (Botkin et al. 1991).

Habitat protection/ownership

One of the largest areas of suitable habitat for Kirtland’s Warbler in Canada occurs at CFB Petawawa, Ontario owned by the Canadian Department of National Defence. Other areas with potential suitable habitat are either Crown Land or First Nations Land (e.g., Manitoulin Island, Thessalon, Cartier to Lake Wanapitei and Chapleau to Gowganda). There are likely vast areas of suitable jack pine habitat, probably on Crown Land and thus protected (to some degree); however, the precise area involved is unknown.

Table 1. Comparison of management practices in jack pine in Michigan vs. Ontario
(Michigan Department of Natural Resources 2007; T. Hogrefe pers. comm. 2007 ).
Management practices Michigan Ontario (Algoma)
Stand size Stands > 1,000 acres (404.7 ha) have higher nesting densities and are used over a longer period. Treatment blocks are > 300 acres (121.4 ha) and > 1,000 acres when possible No specific management for stand size
Fire management Previously used fire to obtain best stand densities for warblers – now timber harvest Mostly planted, fire avoided (liabilities of getting out of control)
Soil type Fine to medium sands (Grayling-Rubicon) Coarse sandy, gravelly soils
Rotation age 55 years (45 years in Upper Peninsula) 75 years
Replanting Replant clearcuts to achieve 75% regeneration (25% open) with 1-5 openings per acre. No specific replanting goal
Natural regeneration May provide cheaper alternative; involves chop and chain green slash; so seeds in cones fall on mineral soil.  
Density Clear cuts are replanted to density of at least 1,089 stems/acre (0.4 ha) or 1,450 stems/acre with openings ?
Edge management Not planted to edge in Lower Peninsula; planted to edge in Upper Peninsula Jack pine is planted to edge (roads etc.); removes foraging habitat
Slash management Slash chipped back into stands in Lower Peninsula, not in Upper Peninsula Delimbed at roadside leaves large piles of slash (rarely burned because of liabilities)
Special protection Stands posted to minimize disturbance in Lower Peninsula; not in Upper Peninsula Not posted

Page details

Date modified: