General Technical Report RMRS-GTR-22
The Northern Goshawk in Utah: Habitat Assessment and Management Recommendations

Background

General Taxonomy and Distribution

Distribution of the goshawk is Holarctic with three recognized subspecies breeding in North America: the northern goshawk (A.g. atricapillus), Queen Charlotte (A.g. laingi), and the Apache (A.g. apache) (USDI Fish and Wildlife Service 1997). The northern goshawk is the most widespread of the three subspecies. This subspecies nests from the boreal forests of north central Alaska and northern Canada to western montane forests in the United States and Northern Mexico (Brown and Amadon 1968). The Queen Charlotte goshawk occurs along the coast and on islands of the Pacific Northwest and on the Olympic Peninsula (Brown and Amadon 1968). The Apache goshawk lives in southern Arizona and Mexico (Brown and Amadon 1968). Goshawks are known to winter throughout their breeding range and as far south as southern California, northern Mexico, Texas, and the northern portions of the Gulf states (Johnsgard 1990).

The goshawk is the largest of the three species of Accipiter in North America. Members of the genus inhabit coniferous, deciduous, and mixed forests. In North America, goshawks vary from deep grey to slate grey and deep neutral grey on their upper parts. The top of the head is often slate black with the sides heavily mottled with white. Adult goshawks have an orange-red eye which becomes deeper red to mahogany in older birds. The female goshawk is larger than the male weighing as much as 3.0 lb with a wing span ranging from 41 to 45 inches. The male weighs up to 2.4 lb with a wing span of 38 to 41 inches (Squires and Reynolds 1997; Wheeler and Clark 1995). Both sexes have short, rounded wings and a long square tail making them well adapted for maneuvering in forested conditions (Reynolds and others 1992).

Historical Distribution in Utah

Little information exists on the historical distribution of goshawks in Utah. Early records indicate that it was an uncommon permanent resident, primarily found in montane conifer and quaking aspen (Populus tremuloides) habitats throughout the State (Behle and others 1985). But occasionally it nests in cottonwood (Populus spp.) cover types in lower valleys (White 1965). Studies and surveys over the past 20 years indicate that the goshawk occurs across the State in a wide variety of forest types.

Characteristics of Occupied Habitats in Utah

Nesting Habitat -- The northern goshawk nests in a wide range of forested habitats, from small clumps of quaking aspen intermixed with sagebrush (Artemisia spp.) in Nevada (Younk and Bechard 1994a) to ponderosa pine (Pinus ponderosa) and mixed conifer forests in northern Arizona (Reynolds and Joy 1998), to temperate rain forests dominated by western hemlock (Tsuga heterophylla) and spruce (Picea spp.) in southeastern Alaska (Iverson and others 1996).

In Utah, most of the 421 known nests located during project level surveys occur in mid-elevation (6,000 ft) to high-elevation (10,000 ft) sites which are currently occupied by mature quaking aspen or coniferous forest. Few nests were found in high elevation Engelmann spruce (Picea Engelmannii) /subalpine fir (Abies lasiocarpa) forests in northeastern Utah. The greatest proportion of the known nests occurs in mixed lodgepole pine (Pinus contorta) and quaking aspen forests (table 1). Engelmann spruce alone or mixed with lodgepole pine is also frequently used for nesting. Goshawk use these forest types even when there is substantial insect-related mortality in the overstory. On the Ashley National Forest in northeastern Utah, many nests occur in lodgepole pine forests where up to 80 percent of the overstory trees are dead as a result of a mountain pine beetle (Dendroctonus ponderosae) outbreaks in the early 1980's (Ashley National Forest 1998a; Dewey 1996; White 1992). The number of young that fledged on these territories from 1989 to 1996 was comparable to the numbers fledged over the same time period for many other populations in the Western United States (Dewey 1996; Kennedy 1997). Similarly, on the Dixie National Forest in southwestern Utah, nesting territories located on areas with high mortality caused by spruce bark beetle (Dendroctonus rufipennes) remained active (Dixie National Forest 1997).

Table 1 -- Proportion of nest stands by potential vegetation type and cover type.

There are some regional differences in goshawk use of certain forest cover types in Utah. In southern Utah, Engelmann spruce and subalpine fir cover types are used frequently for nesting, while in northern Utah these types are only rarely used, except where Engelmann spruce is mixed with lodgepole pine (table 1). Squires and Ruggiero (1996) suggest that in south-central Wyoming, lodgepole pine is preferred over Engelmann spruce/subalpine fir cover types. Both Douglas-fir (Pseudotsuga menziesii) and white fir (Abies concolor) are only moderately used by nesting goshawks, compared to other cover types in the State. Douglas-fir cover types are used somewhat more for nesting in southern Utah compared to northern Utah.

Goshawks only moderately use ponderosa pine for nesting in Utah (table 1), even though it is used extensively by goshawks in northern Arizona (Reynolds and others 1994). Limited use of this type in Utah may be due to the current forest conditions. Many ponderosa pine forests in Utah were partially cut following mountain pine beetle outbreaks in the 1970's. As a result, many large trees were removed, which reduced nesting habitat for goshawks. In northeastern Utah, historical nests were observed in ponderosa pine forests but no active nests have been located since the forests were harvested in the 1980's (Ashley National Forest 1998a). Southern Utah ponderosa pine forests were also partially harvested in the 1980's resulting in large areas of low density, relatively small diameter forests (Dixie National Forest 1997). In these forests there is little evidence of goshawk nesting activity.

Cottonwood, pinyon/juniper (Pinus edulis/Juniperus spp.), Gambel oak (Quercus gambelii) and maple (Acer spp.) woodlands are not known to be used for nesting in Utah. However, Bloom and others (1986) have observed nests in Utah juniper (Juniperus osteosperma) in northeastern California, but noted that ponderosa pine was also present. Oak and oak/maple woodlands in Utah are used by other accipiters, but seem to be avoided by goshawks (Fischer and Murphy 1986; Hennessy 1978). The few nests in cottonwood trees were located in mixed deciduous/coniferous forests not pure cottonwood groves. Although the woodland cover types do not appear to be important for nesting, they may be valuable to goshawks for foraging and roosting during the nonbreeding season.

Nest Site Characteristics -- Goshawks nest in sites with similar structural characteristics within each cover type. In general, goshawks nest in mature to old forests with relatively large trees, high canopy closure (relative to surrounding areas), sparse ground cover and open understories. Nests are often located near the bottom of moderately steep slopes, close to water, and often adjacent to a canopy break (Squires and Reynolds 1997). Important internal components of forests in Utah include snags, multiple canopies, and down woody debris (Reynolds and others 1992). In Utah, these components tend to vary across forest type (table 2). For example, spruce/fir forests have complex forest structures with multiple canopies and large amounts of down woody debris. Lodgepole pine forests have simple forest structures, single canopies and have small amounts of down woody debris except in very old forests.

Table 2 -- Characteristics of known nest sites in Utah by forest cover type (based on descriptions provided by Northern Goshawk Interagency Technical Team members and other listed technical contributors) (appendix A).

Foraging Habitat -- Goshawks prefer to forage in closed canopy forests with moderate tree densities as compared to young open forests (Fischer and Murphy 1986; Squires and Reynolds 1997). Goshawks take prey from openings, although they usually hunt these areas from perches near the edge (Younk and Bechard 1994b). Medium to large-sized birds (woodpeckers, robins, grouse, or jays) and mammals (ground and tree squirrels and hares) tend to dominate breeding season diets (Squires and Reynolds 1997) (fig. 1). The particular species taken varies regionally, but the species groups represented in goshawk diets are usually consistent throughout the Western United States. For example, the red squirrel (Tamiasciurus hudsonicus) and tassel-eared squirrel (Sciurus aberti) group are important prey in the Southwestern United States and a similar group consisting of the Douglas squirrel (Sciurus douglasi) and northern flying squirrel (Glaucomys sabrinus) are important in eastern Oregon and Washington (Reynolds and Meslow 1984; Reynolds and others 1992; Watson and Hayes 1997). Species listed as common prey, regardless of location, include the American robin (Turdus migratorius), Steller's jay (Cyanocitta stellari), northern flicker (Colaptes auratus), blue grouse (Dendragapus obscurus), red squirrel, and golden-mantled ground squirrel (Citellus lateralis) (Reynolds and Meslow 1984; Reynolds and others 1992; Titus and others 1994; Younk and Bechard 1994a). The important prey species identified in Utah from field observations made during the breeding season are similar to those discussed above (table 3). However, due to the lack of data based on direct observations, the variety of mammals in goshawk diets in Utah may be underestimated (Boal and Mannan 1994). However, this list includes several mammals identified as "dominant prey" by Squires and Reynolds (1997), and we feel it is a reasonable representation of goshawk diets in Utah.

Figure 1 -- Fledgling goshawks waiting to be fed.

Table 3 -- Prey species used by nesting goshawks in Utah. (based on descriptions provided by Northern Goshawk Interagency Technical Team members and other listed technical contributors; appendix A).

Reynolds and others (1992) defined desired conditions for foraging habitat on the basis of prey ecology. Their "food web" approach to habitat management received support from technical reviewers (Braun and others 1996). We used this same approach to characterize foraging habitats in Utah, which is based on prey species observed Statewide (table 4).

Table 4 -- Important habitat attributes for maintaining populations of selected goshawk prey in Utah (based on descriptions provided by Northern Goshawk Interagency Technical Team members and others listed technical contributors; appendix A).

Nonbreeding Season Habitat -- Braun and others (1996) noted that reproduction is less important than other factors governing population dynamics. Far more important are mortality and dispersal that occur primarily outside of the breeding season. Unfortunately, little is known about goshawk habitat use in the nonbreeding season. Reynolds and others (1994) radio-tagged adult and juvenile goshawks in northern Arizona and tracked them during fall and early winter. All but one of the adults stayed on their summer ranges during this time. One adult female was relocated in pinyon/juniper woodlands approximately 10 miles from her nest. Most fledglings remained near their natal sites. However, transmitters from two fledglings were recovered in pinyon/juniper woodlands, apparently shed after dispersing from their natal site. Squires and Ruggiero (1995) followed four adult goshawks from their breeding areas in south central Wyoming to wintering areas up to 116 miles away in northern and central Colorado. Habitats used by these goshawks ranged from quaking aspen/mixed-conifer forests to small cottonwood groves surrounded by sagebrush.

The six of 10 female goshawks radio tracked in the Uinta Mountains relocated to pinyon/juniper woodlands near patches of cottonwood during the winter (Ashley National Forest 1998b). These woodlands were located 60 miles from the nest area. However, one female moved to pinyon/juniper woodlands near the LaSal Mountains in southeastern Utah, approximately 190 miles from her nest area (Squires 1997). Four females remained in their nest areas, or in similar habitat less than 10 miles away. Not all radio-tagged females were located, so it is not known if these locations are truely representative of winter habitat use for most goshawks breeding in the Uinta Mountains (Ashley National Forest 1998b; Squires and Ruggiero 1995).

Overwintering strategies for goshawks may be related to food availability. Doyle and Smith (1994) observed goshawks on their Yukon study area year-round during periods of high snowshoe hare (Lepus americanus) populations, but noted that goshawks almost disappeared during winters when hare numbers were low. McGowan (1975) also speculated that cyclic prey abundance accounted for observed fluctuations in goshawk numbers in interior Alaska, especially during the winter. However, this may be less important in the Western United States where the goshawk's primary mammalian prey are less cyclic (McGowan 1975). Populations of snowshoe hares appear to be considerably more stable in the Central Rocky Mountains than in Canada (Dolbeer and Clark 1975). Because red squirrels are able to avoid starvation during food shortages by caching food, their populations also remain relatively stable (McGowan 1975). The diversity of prey taken in the Western United States may buffer goshawk populations against extreme fluctuations in individual prey species (Boal and Mannan 1994).

Weather may also be a factor in determining when and how far goshawks migrate to winter ranges. Squires and Ruggiero (1995) noted that a long distance movement of goshawks coincided with a major snowstorm. Severe weather conditions may increase the importance of thermal cover for goshawks, and deep snow cover may limit the kind and amount of prey available. Either situation may cause goshawks to seek out different habitats in the winter.

Factors Influencing the Species

History of Goshawk Conservation Efforts -- As a result of studies conducted on nesting habitat in the 1970's (Bartelt 1977, Hennessy 1978) several threats facing the goshawk were recognized (Reynolds 1989). In the 1980's, the USDA Forest Service designated the goshawk as a national indicator of mature and old-growth forests. Subsequently, at least 49 National Forests selected the goshawk as a management indicator species used in Land Management Plans (Patla 1990; Sidle and Suring 1986).

This led to the development of management recommendations for western coniferous forests to protect nest sites (Reynolds 1983). These recommendations proposed that a 20 acre buffer of uncut habitat be left in timber sale areas around two active and two replacement nest sites per nest area. In Arizona, an evaluation of the 20 acre buffer indicated that these small areas were not protecting nest areas adequately when implemented (Crocker-Bedford 1990; Crocker-Bedford and Chaney 1988). In 1992, more comprehensive management recommendations for the goshawk were developed for the USDA Forest Service, Southwestern Region (Reynolds and others 1992). This effort recommended managing for 6,000 acre territories to protect nests and provide adequate foraging habitat. During this same time period, Kennedy and Stahlecker (1993) developed and tested a calling protocol for locating breeding goshawks.

Livestock Grazing -- Domestic livestock have grazed Southwestern ponderosa pine and mixed-species forests since the mid 1800's (Cooper 1960; Rasmussen 1941) and has affected both forest structure and composition. Within ponderosa pine forests, dense grass cover can decrease seedling establishment and survival (Brawn and Balda 1988). However, heavy livestock grazing reduced ground cover, which encouraged the establishment of dense stands of saplings (Covington and Moore 1991; Reynolds and others 1992; Stein 1988). Fire suppression also allowed trees to encroach into openings, subsequently reducing forage production. Grazing in high elevation meadows and open parklands has changed plant community composition and structure. These changes most likely have affected goshawks, but the extent of that effect is poorly documented.

In Nevada, livestock grazing resulted in the deterioration and loss of some goshawk nesting habitat (Herron and others 1985; Lucas and Oakleaf 1975). Annual grazing by concentrated livestock removed young stems and reduced quaking aspen's ability to regenerate (Mueggler 1989). Surveys in Nevada indicate that 85 percent of the known goshawk nests in the Humboldt/Toiyabe National Forest were found in quaking aspen forests. In addition, 70 percent of all quaking aspen in Nevada is located on USDA National Forest System administered lands and the majority of these forests have minimal regeneration (USDA Forest Service 1993). Grazing also alters both the structure and species composition of the grass, forb and shrub layers of quaking aspen forests which also modifies goshawk foraging habitat (Reynolds and others 1992).

Riparian areas are the most productive and valuable wildlife habitats wherever they occur. During the past century, 70 percent of the wetland/riparian areas have been negatively impacted throughout the West (Lee and others 1989). Continued loss of forested riparian wetlands in the Rocky Mountain States averages 1 percent per year or more (Lee and others 1989). Because goshawks use riparian areas for both nesting and foraging, reductions caused by livestock grazing can negatively affect habitat for goshawk prey and reduce or eliminate foraging habitat potential (Hargis and others 1994; Patla 1994; Reynolds and others 1992).

Fire Suppression -- Goshawk foraging and nesting habitat has also been impacted by fire suppression. Throughout Western North America, prior to European settlement, ponderosa pine forests burned every 2 to 15 years. These fires were typically low-intensity, lightning caused, noncatastrophic surface fires (Avery and others 1976; Cooper 1960, 1961; Covington and Moore 1991; Dieterich 1980a, 1983; Gruell and others 1982; McCune 1983; Reynolds and others 1992; Swetnam 1988; White 1985 ). Both stand replacing and surface fires occurred in mixed-conifer forests at 5 to 22 year intervals (Ahlstrand 1980, Weaver 1951, Wright 1988). Effective wildfire suppression since the 1900's has changed fire regimes, and in some areas, entirely eliminated them (Dieterich 1980b, Keane and others 1990, McCune 1983, Stein 1988, Weaver 1961).

Low intensity surface fires typically maintained open conditions in dry forests by continually cleaning the forest floor of small trees and lower vegetation, allowing for easy hunting access. The lack of fire in ponderosa pine forests has resulted in stands dominated by multiple canopies containing one or more cohorts of Douglas-fir, white fir, or ponderosa pine. Likewise, the lack of fire has resulted in the failure of seral quaking aspen stands to regenerate; instead they are being replaced by firs and spruce (Bradley and others 1992). As stocking levels increase, "ladder" fuels that carry fires from the surface into the crowns develop (Madany and West 1980). This condition, combined with a build-up of surface fuels, produces severe and intense crown fires. Prior to European settlement, large stand replacing events were thought to be rare, especially in ponderosa pine forests and possible other forest types (Brawn and Balda 1988; Covington and Moore 1991).

Timber Harvest -- Goshawks can breed successfully in forests where timber harvesting has occurred (Reynolds and others 1994; Woodbridge and Detrich 1994) but they appear to prefer stands of mature and over-mature trees for nesting and foraging (Bright-Smith and Mannan 1994). Also, occupancy of the nest stand has been positively associated with patch size (Woodbridge and Detrich 1994). However, the effects of reducing the number and size of mature trees on existing goshawk densities or productivity is unknown. Population models for species in fragmented forest landscapes suggest that sharp declines in viability can occur if habitat decreases over the long-term (Franklin and Forman 1987; Lamberson and others 1992). The removal of suitable nesting habitat through timber harvesting or other management activities can be a threat to the goshawk (McCarthy and others 1989; Moore and Henny 1983; Reynolds 1989). Evidence suggests that timber harvesting on the North Kaibab Ranger District in Arizona caused goshawks to decline from an estimated 260 nesting pairs to 60 nesting pairs (Crocker-Bedford 1990). Due to commercial timber and fuel wood harvesting, snags and large trees are less abundant in present-day forests.

Insect and Disease Outbreaks -- The history of Southwestern forests, particularly fire suppression and timber harvesting, has altered the forest structure and composition in a manner that facilitates insect and disease outbreaks (Parker 1991; Reynolds and others 1992). Insects and diseases, along with fire, are among the more important regulators of forest density, composition, and structure. Observations on the distribution and the severity of insects and disease outbreaks prior to the past few decades are limited. Evidence indicates that dwarf mistletoes (Arceuthobium spp.) and root diseases (Armillaria spp., Heterbasidian spp.) are increasing in Southwestern forests (Parker 1991) due to high stand densities and species composition changes. As a result of these changes, the potential for large scale epidemic outbreaks of bark beetles (Dendroctonus spp.) is present in many ponderosa pine and mixed species forests (Gardner and others 1997; Hedden and others 1981; Rogers and Conklin 1991). Endemic levels of insects and pathogens can play significant ecological roles by causing tree mortality, defoliation, decay, or deformity, that are often important attributes for goshawk nesting or foraging.
The composition and structural changes in the forests of Utah have increased epidemic frequencies of insects. For example, the Engelmann spruce forests on the Dixie and Manti-LaSal National Forests are currently experiencing spruce bark beetle epidemics. As a result, trees 4 inches and larger are being killed in 5 to 10,000 acre patches. In northern Utah, similar epidemics of mountain pine beetle occurred in 10,000 acre patches in lodgepole pine, affect about 100,000 acres total. Goshawk continue to nest successfully in these beetle-killed forests (Ashley National Forest 1998b; Dewey 1996; Dixie National Forest 1997).

Competition, Predation, and Disease -- Nesting habitat structure with open conditions may allow for the predation of goshawks, and especially their nestlings, by great horned owls (Bubo virginianus) (Boal and Mannan 1994; Crocker-Bedford 1990; Moore and Henny 1983; Woodbridge and Detrich 1994). Nestling mortality may increase during periods of low food availability (Crocker-Bedford 1990; Moore and Henny 1983; Rohner and Doyle 1992; Woodbridge and Detrich 1994; Zachel 1985). Moreover, the pine marten (Martes americana) and fisher (Martes pennanti) can also be predators (Patla 1990).

Open habitat may lead to the replacement of nesting goshawks by red-tailed hawks (Buteo jamaicensis) and great horned owls (Crocker-Bedford 1990; Moore and Henny 1983). Great horned owls and the long-eared owls (Asio otus) can use goshawk alternate nests (Buchanan and Erwin 1997; Bull and others 1988; Dewey 1996; Dixie National Forest 1997; Patla 1992; Woodbridge and Detrich 1994). In northern California, goshawks moved after their nests were occupied by spotted owls suggesting possible competition for nest sites (Woodbridge and Detrich 1994).

Goshawks will attack red-tailed hawks, short-eared owls (Asio flammeus), and great horned owls when near nests (Cranell and Destefano 1992; Lindberg 1977). Raptors killed by goshawks include long-eared owls, tawny owls (Strix aluco), nestling honey buzzards (Pernis apivorus), nestling and adult common buzzards, nestling and adult sparrowhawks (Accipiter nisus), other goshawks, and red-tailed hawks, American kestrel (Falco sparverius), Cooper's hawk (Accipiter cooperii) and sharp-shinned hawk (Accipiter striatus) (Kostrzewa 1991; Reynolds and others 1994; White 1998). On the Dixie and Uinta National Forests, goshawks have been observed defending nest territories against both red-tailed and Swainson's hawks (Buteo swainsoni) (Dixie National Forest 1997).

Goshawks have several diseases and body parasites that may impact nesting and brooding success. Tuberculosis and fungal diseases are typically found in goshawks (Squires and Reynolds 1997). Goshawks are plagued by ectoparasites such as lice, and internal blood parasites such as Leucocytozoon, Haemoproteus, Trypanosoma, and microfilariae. Approximately 56 percent of North American goshawks suffer from such internal parasites (Greiner and others 1975) but how they impact goshawk populations is unknown.

Title: Background: RMRS-GTR-22 - The Northern Goshawk in Utah: Habitat Assessment and Management Recommendations
Electronic Publish Date: May 26, 1999
Expires: Indefinite
Last Update: January 15, 2002

RMRS Publications | Order a publication | Contact Us