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COSEWIC Assessment and Update Status on the Northern Goshawk (2000)

Habitat

General

Goshawks are habitat generalists on large spatial scales, but have a complexity of habitat needs during the breeding season, the specifics of which vary among forest types and regions (Johnsgard 1990). Although goshawks may breed in younger, more even-aged stands, they tend to choose breeding areas which have stands with relatively large amounts of mature or old-growth trees or stand characteristics (Squires and Reynolds 1997; McClaren 1998). These stands do not necessarily need to be continuous, but substantial amounts seem to be preferred. 

Eight characteristics common to the goshawk nesting area in western North America include: 1)presence of mature to old-growth forests; 2) canopy closure >60%; 3) open understory; 4) gentle to moderate slopes of <40%, (nests are generally on benches, slope toes or level ground); 5) lower third or bottom of slope; 6) northerly exposure, northeast to northwest; 7) often close to a perennial water source; and 8) proximity to an abundant prey base (Marshall 1992; Duncan and Kirk 1995). Larger diameter at breast height (dbh) trees are also thought to be important (Daw et al. 1998).

High canopy closure is the single most consistent nesting habitat feature for goshawks across their range (Squires and Reynolds 1997; Daw et al. 1998). Relatively closed stands provide protection from predators and promote more open spaces under the canopy that allows clear flight paths for striking prey. Small forest openings, such as where one or two trees have fallen and left more open air space near the nest tree, are often associated with nest sites (Reynolds et al. 1982). On the Queen Charlotte Islands, all nests of the Queen Charlotte Goshawk found recently have occurred in small forest openings (Chytyk and Dhanwant 1997); a characteristic also noted for some nests on Vancouver Island (E. McClaren pers. comm.).

Nesting Habitat

Stands used for nesting vary in size and shape, depending on topography and availability of suitable stands. Nests were usually situated on benches or slopes with a gentle to moderate incline (<40%), and at the bottom or lower 1/3 of the slope (Duncan and Kirk 1995). On Vancouver Island, Queen Charlotte Goshawk nests were generally located on the bottom two-thirds of a slope, at lower elevations of moderate slopes (McClaren 1999). Forty active or alternate nest trees on Vancouver Island averaged an elevation of 392 m (McClaren 1998). On the Queen Charlotte Islands, 5 active nests were found in the bottom third of gentle slopes, average elevation of 178 m and slope of 26° (Chytyk and Dhanwant 1999; Chytyk et al. 1999).

In temperate forests of North America, nest stands tend to face north, but in boreal forests, southern aspects may be preferred (Speiser and Bosakowski 1987; Doyle and Smith 1994). Considerable variation occurs in British Columbia. Goshawks in the Kispiox Forest District of northwestern interior British Columbia preferred northeast-facing slopes (Mahon and Franklin 1997), whereas Queen Charlotte Goshawks on the Queen Charlotte Islands, which is at the same latitude as Kispiox, used only southwest-facing slopes (Chytyk and Dhanwant 1999; Chytyk et al. 1999). On Vancouver Island, Queen Charlotte Goshawks nested on all aspects (McClaren 1999). Although the sample from the Queen Charlotte Islands was small, there may be a significant difference in aspect preference between Queen Charlotte Goshawks on Vancouver Island and those on the Queen Charlotte Islands.

Stands used for nesting generally have trees that are taller and older than in surrounding forests. These stands typically have a relatively high proportion of larger trees and a higher canopy closure (Reynolds et al. 1982; Moore and Henny 1983; Speiser and Bosakowski 1987; Crocker-Bedford and Chaney 1988; Iverson et al. 1996; Bosakowski and Rithaler 1997; McClaren 1998; Chytyk and Dhanwant 1999). Canopy closure has been documented to range from 51% to 94%, but is almost always >60%. High canopy closure may provide protection from avian predators such as Red-tailed Hawks (Buteo jamaicensis), Great Horned Owls (Bubo virginianus), and corvids (Moore and Henny 1983; Crocker-Bedford and Chaney 1988; Crocker-Bedford 1990b), provide thermal cover (Reynolds et al. 1982; Hall 1984), and promote more open spaces under the canopy and in the undergrowth that allows clear flight paths (Squires and Reynolds 1997).

On Vancouver Island, of 56 Queen Charlotte Goshawk nests, 62% were found in contiguous old-growth forests, 25% in contiguous second-growth forests, and 13% in fragmented old-growth forests (McClaren 1999). The youngest-aged stand which contained a nest was 53 years. On the Queen Charlotte Islands, 4 Queen Charlotte Goshawk nests were found in contiguous western hemlock (Tsuga heterophylla) old-growth stands (Chytyk and Dhanwant 1999), while another active nest was found in contiguous western hemlock old-growth forest that was bordered by mature western hemlock that contained 2 alternate nests (Chytyk et al. 1999). In southeast Alaska, minimum amounts of old-growth forests in Queen Charlotte Goshawk use areas (areas in which radio locations were made of radio-tagged nesting birds) were 23% and 28% for males and females respectively. In areas with less than those amounts of old-growth forest there was no use (Iverson et al. 1996); however, the study area contained virtually no mature forest (K. Titus pers. comm.).

Goshawk nest trees tend to be the largest, or one of the largest, trees in the stand (Reynolds et al. 1982; Speiser and Bosakowski 1987; Squires and Ruggerio 1996; Daw et al. 1998; Rosenfield et al. 1998; Bosakowski 1999). In British Columbia, this trend also occurred with the Queen Charlotte Goshawk (McClaren 1998; Chytyk and Dhanwant 1999; T. Ethier pers. comm.). Larger trees provide structural support for nests including: strong lateral branches, crotches, or defects, such as broken tops or mistletoe structures. In pole-stage Douglas-fir (Pseudotsuga menziesii) forests in western Washington, where tree branches did not provide suitable nest sites, mistletoes or tree deformities provided structural support for nests (Fleming 1987). On the Queen Charlotte Islands, several Queen Charlotte Goshawk nests were located on mistletoe structures on dead old-growth western hemlocks (Chytyk and Dhanwant 1997). See Appendix A for a summary of nest tree characteristics from selected studies in North America.

A variety of coniferous and deciduous tree species are commonly used by goshawks as nest trees: Oregon - ponderosa pine (Pinus ponderosa), lodgepole pine (P. contorta), Douglas-fir and western larch (Larix occidentalis) (DeStefano and Meslow 1992; Reynolds et al. 1982; Bull and Hohmann 1994); southeast Alaska - Sitka spruce (Picea sitchensis) and western hemlock (Titus et al. 1994); interior Alaska - paper birch (Betula papyrifera) (McGowan 1975); Yukon - spruce or trembling aspen (Populus tremuloides) (Doyle and Smith 1994). In British Columbia, records of nest trees included mainly trembling aspen and Douglas-fir, but black cottonwood (P. balsamifera trichocarpa), western larch, ponderosa pine, lodgepole pine, paper birch and spruce were also used (Campbell et al. 1990; T. Antifeau pers. comm.). In the Cariboo Region, nest trees included Douglas-fir, lodgepole pine, and trembling aspen (Bosakowski and Rithaler 1997). In the Kispiox Forest District, nests were in mature or old-growth western hemlock or amabilis fir (Abies amabilis) (Mahon and Franklin 1997).

On Vancouver Island, most nest trees were live Douglas-firs and western hemlocks, however, red alder (Alnus rubra), Sitka spruce and western redcedar (Thuja plicata) were also used (McClaren 1999). The variety of nest tree species selected by Queen Charlotte Goshawks on Vancouver Island suggests that they may select for forest and nest tree structure, not nest tree species (McClaren 1999). On the Queen Charlotte Islands, 4 of 5 active nests were in dead western hemlocks, while the fifth was in a live western hemlock (Chytyk et al. 1999). Both western hemlock and Sitka spruce were used as alternate nest tree species on the Queen Charlotte Islands.

Foraging Habitat

Goshawks require relatively large foraging areas due to the relative scarcity of their prey and, consequently, they generally have large breeding season home ranges. Typically, goshawk prey species diversity decreases with increasing latitude (Johnsgard 1990); as a result, there is a general trend of increased breeding season home range size with higher latitude. Also, prey species diversity is lower on Vancouver Island and Queen Charlotte Islands compared to the adjacent mainland because of lower prey species diversity on coastal islands (Stevens 1995). In southeast Alaska, median breeding season use areas for males and females varied between 4,400 and 3,600 ha respectively (Titus et al. 1996). Elsewhere, home ranges were approximately 5000 ha in the foothills of Alberta (Schaffer et al. 1996); from 1842 to 4214 ha on the Olympic Peninsula in Washington (Finn et al. 1998); from 1083 to 6908 ha in Oregon (Austin 1993); from 860 to 2530 ha (Bright-Smith and Mannan 1994) or 2025 to 2430 ha in Arizona (Reynolds et al. 1992); and were 1550±890 ha in California (Hargis et al. 1994). Winter home ranges are poorly described.

Prey abundance and prey availability drive the use of foraging habitat, and prey availability is usually affected by vegetation structural attributes. Consequently, goshawks forage in areas that have the following attributes: 1) adequate prey; 2) sufficient cover to conceal the goshawk’s approach to prey; 3) sufficient openings in cover so that prey cannot escape or flight paths are not obstructed; and 4) suitable perches available for the goshawk’s spot and attack hunting method (Beebe 1974; Kenward 1982; Reynolds and Meslow 1984; Widen 1989; Johnsgard 1990; Beier and Drennan 1997; Squires and Reynolds 1997). When prey are particularly abundant, natural openings, forest edges, clearcuts and even agricultural lands may be used for foraging. However, goshawks may be excluded from these niches by other raptor species, such as Red-tailed Hawk, which are better adapted to treeless environments (Kenward and Widen 1989; Widen 1989; Crocker-Bedford 1990a; Marshall 1992).

Goshawks forage in all layers of a forest, from the ground up to the aerial zones above the canopy, but tend to concentrate efforts in the ground-shrub layer (Reynolds and Meslow 1984). The large body size and hunting strategies of goshawks precludes the use of young, densely stocked stands for foraging (Reynolds et al. 1982; Moore and Henny 1983; Hayward and Escano 1989; Duncan and Kirk 1995; Squires and Ruggerio 1996). Therefore, regenerating early seral stages are less suitable as foraging habitat. Clearcuts may be used for foraging until trees reach a size where goshawks cannot easily penetrate stems or foliage. For example, in an intensely harvested forest in western Washington, Blue Grouse (Dendragaous obscurus) occurred abundantly in regenerating clearcuts. They also represented a relatively high proportion of goshawk diet (Bosakowski et al. 1999) compared to goshawks in less intensely-harvested U.S national forests where they relied more on forest-interior birds (Reynolds and Meslow 1984; Bull and Hohmann 1994).

Although edges, small open areas, and clearcuts (Bosakowski et al. 1999) can be used for foraging, and seem to be regularly used by goshawks in interior British Columbia (Beebe 1974), the Queen Charlotte Goshawk seems to use unbroken forests more frequently for foraging, and have less association with edges (Iverson et al. 1996). In southeast Alaska, Queen Charlotte Goshawks showed a strong preference for old-growth and mature forests, and tended to avoid early successional stands and clearcuts (Titus et al. 1994, 1995). On Vancouver Island, three territorial male Queen Charlotte Goshawks showed variable use of old-growth and second-growth habitat in 1997; one male consistently used only old growth, while two other males used second growth more than old growth (E. McClaren, unpubl. data). The second-growth stands were mostly between 60 and 100 years old, but stands as young as 40 years old were used occasionally. These data cannot be used to infer that younger stands are used more often by some individuals since there were no data on use versus habitat availability; however, it is apparent a variety of habitats are used for foraging. During winter 1997, radio-tagged Vancouver Island birds mainly frequented large contiguous stands of old growth and >60 year old second growth (D. Doyle pers. comm.).

Trends in Habitat Quality

In coastal British Columbia, second-growth stands on good growing sites can become suitable for nesting Queen Charlotte Goshawks after >50 years, as several nests have been found in such stands on Vancouver Island (McClaren 1999; D. Doyle pers. comm.). If logging rotations of 100 years were standard, then provision of extensive amounts of suitable second-growth breeding habitat could be ensured. However, it is becoming increasingly common for second-growth stands that are 50‑60 years, and which have size and structure suitable for goshawks, to be logged because of the timber values represented by trees of that size. The result is that once an old-growth stand is logged, it may be continually logged as second growth just as it is becoming suitable for goshawks. Consequently, these stands would not recover sufficiently to provide habitat suitable for nesting goshawks.

On Vancouver Island, Queen Charlotte Goshawk nests that were in contiguous second growth and fragmented forests generally had a lower re-occupancy rate than nests in contiguous old growth. In 1998, 25% of 8 nests in contiguous second growth and 20% of 5 nests in fragmented forests were re-occupied, compared to 83% of 12 nests in contiguous old-growth forests (McClaren 1999).

Protection/Ownership of Habitat

Considerable amounts of forested land on Vancouver Island and the Queen Charlotte Islands are protected from logging by virtue of being in national parks, provincial parks, ecological reserves, or other protected areas (Table 1). On the Queen Charlotte Islands, about 96% of protected forests are in two reserves, Naikoon Provincial Park (69,198 ha, ne corner of Graham Island) and Gwaii Haanas National Park Reserve (148,658 ha, southern portion of Moresby Island).

On Vancouver Island, Strathcona Provincial Park (253,773 ha) is the single most significant protected forested area, but in recent years, many new areas totalling over 150,000 ha, most of which are forested, have been given protected status through the British Columbia Protected Areas Strategy (LUCO 1996). Over 99,000 ha in 47 parcels, mainly in northern and western Vancouver Island, have been protected from logging between 1992 and 1996. Of these 47 parcels, 14 are over 1,000 ha, with the largest being 22,800 ha. In addition, over 63,000 ha in 15 parcels have been conserved in the Clayoquot Sound area, near Pacific Rim National Park.

Table 1:  Percentage of Forests in Protected Areas on Vancouver Island and the Queen Charlotte Islands
[data from BC Ministry of Forests (MOF) and BC Land Use Coordination Office (LUCO)*]
 % of forested land base in protected areas
(all BEC zones)
% of low elevation (CDF, CWH) forested land base in protected areas% of high elevation (MH) forested land base in protected areas
Vancouver Island11.89.828.0
Queen Charlotte Islands22.423.016.8

* Data were derived from an interpretation of the biogeoclimatic units that are predominately forested (Del Meidinger, MOF Research Branch, pers. comm.) over-layed with the protected areas (from LUCO).

Unfortunately, few assessment of Queen Charlotte Goshawk populations or habitat suitability has been conducted in these protected areas. Therefore, the relative value to goshawks of most of these protected lands is uncertain. It is likely that some protected areas contain relatively large amounts of suitable goshawk habitat, whereas others with high proportions of high elevation forests, very steep and/or rocky terrain contain little suitable habitat. Two nests were found in Strathcona Park, Vancouver Island in 1995, and some inventory was conducted, with no nests found, in Schoen Lake Park, Vancouver Island in 1996 (E. McClaren pers. comm.).

Forested lands that do not occur in protected areas (88% on Vancouver Island, 78% on Queen Charlotte Islands) are either privately-owned or are part of Tree Farm License (TFL) areas that are leased to industry. There are few controls on harvesting of forests on private lands; essentially landowners have few, if any, restrictions on what they can harvest. In forests leased to industry, provisions for maintaining biodiversity values in the TFL area fall under the BC Forest Practices Code (Ministry of Forests 1995). Of particular importance to the Queen Charlotte Goshawk, 7-28% of the forested land base must be retained as old forest, depending on whether an area is classed as a low to high biodiversity emphasis (Ministry of Forests 1995).

The Queen Charlotte Goshawk has been “identified” by the Chief Forester and the Deputy Minister of Environment, Lands and Parks as requiring special attention under the Forest Practices Code.  As Identified Wildlife, it is part of the Identified Wildlife Management Strategy (IWMS) (Province of British Columbia 1999). This strategy contains specific management practices referred to as General Wildlife Measures (GWMs) that outline what forest and range practices can occur within designated species-specific conservation areas called Wildlife Habitat Areas (WHAs). For the Queen Charlotte Goshawk, the establishment of a “three-tiered” WHA (total 2,400 ha) at selected breeding sites and associated foraging areas is recommended. Three suitable and three replacement nest areas of 12 ha each are restricted from any forest practices. Limited timber harvesting is permitted within the rest of the WHA during specified times (outside the courtship and nesting period for active nests) and in a manner that adheres to a specified distribution of seral stages. This distribution includes 20% closed canopy old forest, 40% mature forest and not more than 20% young forest. The definition of young, mature and old forests varies with natural disturbance type and biogeoclimatic zone; all definitions can be found in the Biodiversity Guidebook (Ministry of Forests 1995).

However, a planning threshold has been implemented that will prevent the unlimited application of WHAs for Queen Charlotte Goshawks. Each forest district will have a 1% threshold on the timber impact associated with the application of WHAs, for all species of “identified” wildlife, not just Queen Charlotte Goshawks. In effect, this amounts to a limit of only a handful of WHAs available for conservation of Queen Charlotte Goshawk habitat in British Columbia, given that a WHA may be as large as 2,400 ha. This threshold will be in effect for two years, or until conservation assessments are developed that can aid in the redistribution of the provincial 1% limit between forest districts. Establishment of WHAs can only thus be expected to conserve habitat for a few pairs of Queen Charlotte Goshawks.

The use of riparian management areas (RMAs), wildlife tree patches (WTPs), sensitive areas, and management for vegetative species composition and coarse woody debris, present additional opportunities to protect goshawk nest sites and suitable foraging habitat (Ministry of Forests 1995). In addition, since old forest retention recommendations are specified for dominant forest covers within natural disturbance types, landscape units can potentially be managed to maximize the retention of suitable goshawk habitat.