Accipiter gentilis (Linnaeus, 1758)
Basis for Listing
The Northern Goshawk (Accipiter gentilis) has a holarctic distribution. Within North America, it breeds in the forested portions of Alaska and Canada and in the upper midwest, western, and northeastern regions of the continental United States. Within Minnesota, Northern Goshawks are found year-round in the north-central and northeastern portions of the state (Laurentian Mixed Forest Province). They prefer contiguous areas of mature and older forest for nesting and foraging (Boal et al. 2005a) and have large home ranges of about 65 km² (25 sq. mi.) per mated pair (Boal et al. 2003).
Since the pre-settlement time period, the availability of large patches of mature and older forest has declined regionally due to fragmented land ownership and the fragmentation of historically large contiguous forest stands due to past and current forest management practices (Host and White 2003; Manolis 2003; White and Host 2003). A study in northern Minnesota found an average net loss of 26% of upland mature/old forest habitat within eight Northern Goshawk territories between 1996 and 2006 (Crozier and Hamady 2008a). The vast majority of known Northern Goshawk breeding territories are located in National and State Forests; however, search efforts outside of these forests have been limited. Forest plans for public lands in Minnesota project a decrease in the older forest utilized by Northern Goshawks in coming decades, specifically substantial decreases in the amount of older aspen (Populus spp.), red pine (Pinus resinosa), and jack pine (Pinus banksiana) forest on state lands (Minnesota Department of Natural Resources 2016).
Limited systematic surveys for Northern Goshawks have occurred in Minnesota. However, the increased survey effort for Northern Goshawk nests since 2003 has found an average of 29 territories with nest attempts per year in the state. Since 1991, 168 territories have been identified in Minnesota. An average of 79% of occupied territories in the current year were occupied in the previous year, emphasizing the ongoing importance of existing territories to this species. Nest success and productivity rates in Minnesota appear to be lower than other areas of the country (Squires and Reynolds 1997), with productivity rates averaging 1.5 young per successful nest (Crozier and Hamady 2013). Given the concerns about habitat availability and the likely effect on nest success, the Northern Goshawk was designated a species of special concern in Minnesota in 2013.
The Northern Goshawk is listed as “Least Concern” globally by the International Union for Conservation of Nature (IUCN) due to its large global range and population size. Within North America, it has a moderate conservation score (11 out of 20 by Partners in Flight) due to its wide distribution, and it is an Audubon Priority Bird Species. Within the Great Lakes region, the Northern Goshawk has been identified as an important species for conservation efforts. It is a U.S. Fish and Wildlife Service Midwest Region Species of Concern and a U.S. Forest Service Sensitive Species in many national forests, including the Chippewa and Superior National Forests in Minnesota. The Northern Goshawk is a Special Concern species and Species in Greatest Conservation Need in Minnesota, Wisconsin, and Michigan, and it is an Audubon Minnesota Priority Species.
The Northern Goshawk is a large-bodied forest-dwelling hawk with broad wings and a long rounded tail. It is the largest of the three accipiters (forest hawks adapted to fast flight) found in Minnesota, and it is adapted to maneuvering and hunting in forests. Adult females are larger than adult males. The adult has a brown-gray to bluish-gray back and a pale gray to white breast and belly, with fine streaking. The head has a dark cap, with a pronounced white stripe above red eyes. The undertail coverts are white and often fluffy when alarmed. The tail is dark gray above, with 3-5 broad dark bands and a thin white band on the rounded tip. Northern Goshawks attain complete adult plumage at 2-years of age. Immature Northern Goshawks have a brown mottled back and a heavily brown and white streaked breast and belly. The immature Northern Goshawk’s eye stripe is pale white above yellow eyes and is less pronounced than in the adult. It can be difficult to distinguish immature Northern Goshawks from immature Cooper’s Hawks (Accipiter cooperi). The goshawk may also be identified by its call, which is a sharp and repetitive "kak-kak-ka".
The Northern Goshawk is most commonly found in larger tracts of mature and older upland forest. Preferred cover types for foraging include aspen, paper birch (Betula papyrifera), red pine, and white pine (Pinus strobus) forests >50 years old and spruce (Picea spp.), balsam fir (Abies balsamea), and jack pine forests >25 years old (Boal et al. 2005a). Forests used by Northern Goshawks for nesting and foraging are similar and tend to have closed canopies, substantial shrub cover, large amounts of snags and woody debris, open flight paths between the canopy and understory layers and between the understory and shrub layers, and high canopy and understory stem densities (Boal et al. 2005a). Nesting areas tend to have taller and larger diameter trees and fewer understory trees than foraging areas. The majority of goshawk nests are located in northern fire-dependent forest and northern mesic hardwood forest. Nesting areas typically have 1-5 alternative nests located within 235 m (771 ft.) of each other (Crozier and Hamady 2008b). Nests are typically located in the tallest (average 21.9m [72 ft.]) and largest diameter (average 39.0 cm [15 in.]) trees in the stand (Boal et al. 2005a). The majority of nests are located in aspen trees (73%), with the rest built in (by order of frequency of use) paper birch, red pine, sugar maple (Acer saccharum), white pine, and jack pine trees (Crozier and Hamady 2013). Foraging areas have a slightly more open canopy and smaller trees than nesting areas (Boal et al. 2005a). Little information is available about the vegetation structure and composition in post-fledging areas in Minnesota.
Biology / Life History
Northern Goshawks are widely, but sparsely, distributed in Minnesota and the western Great Lakes region (Bruggeman et al. 2011). The Northern Goshawks that breed in Minnesota are year-round residents (Boal et al. 2003). Migrant birds come south into Minnesota in the fall, and there is a large influx of fall migrants approximately every ten years due to cyclic prey population dynamics in boreal forests in Canada (Evans et al. 2012). Based on prey deliveries to nests in Minnesota, the Northern Goshawk’s diet consists of a variety of moderately sized mammals and birds; Red Squirrels (Tamiasciurus hudsonicus), Snowshoe Hares (Lepus americanus), Eastern Chipmunks (Tamias striatus), Ruffed Grouse (Bonasa umbellus), and American Crows (Corvus brachyrhynchos) being the most common prey species (Smithers et al. 2005). Northern Goshawks are low-density breeders; the shortest documented distance between two active goshawk nests in Minnesota is 2.8 km (1.75 mi.; Crozier and Hamady 2008b). The species is highly territorial during the breeding season, aggressively defending their nests with calls, dive-bombing, and even attacking intruders. Northern Goshawks exhibit strong mate and nest site fidelity and may use the same nesting area for years (Crozier and Hamady 2013). Nesting Northern Goshawks are typically in full adult plumage (~2 years old), but occasionally birds in juvenile plumage are observed. Courtship behaviors and nest building begin in March. Nests are typically about 60-90 cm (2-3 ft.) in diameter and built in the main crotch of a tree. Nests are made of sticks and often contain green evergreen sprigs and downy feathers. Whitewash and prey remains are often found on the forest floor beneath the nest. Two to four eggs are typically laid in early or mid-April. The female does most of the incubating, while the male provides food. Incubation takes 28-30 days, and the young typically fledge in late June or early July. Monitoring results in Minnesota have shown an average productivity rate of 1.05 young per nest (Crozier and Hamady 2013). The fledglings continue to remain dependent on the parents for food for about six weeks after fledging. During this time period, they learn how to hunt and increasingly spend time away from the nest.
Conservation / Management
The most significant threats to Northern Goshawks in Minnesota are habitat degradation due to fragmentation of large patches of habitat, reduction in the amount of mature and older forest on the landscape, and simplification of forest stands in terms of plant species diversity and stand structure. These factors reduce the amount of suitable habitat available for goshawks and create changes in prey abundance and vulnerability. Fragmentation of habitat and the creation of large openings in the forest increase the vulnerability of goshawks to open habitat predators and competitors such as Great Horned Owls (Bubo virginianus) and Red-tailed Hawks (Buteo jamaicensis). Juvenile and female goshawks are particularly vulnerable to predators during the incubation and nestling/fledgling periods. An additional threat to Northern Goshawks is human disturbance at nest sites during the breeding season.
Maintaining contiguous forested areas with high amounts of canopy closure is necessary to provide adequate resources for Northern Goshawks (Bruggeman et al. 2011). High quality habitat consists of mature closed canopy forest, with large diameter trees, high amounts of woody debris and snags, and substantial shrub and understory cover. Managing for forested stands with high species and structural diversity, as appropriate for the Native Plant Community, is important. Forested landscapes should be managed for a variety of forest types, age classes, and patch sizes to support abundant prey populations. Managing for larger patches of mature forest within these landscapes provides the forest structure suitable for goshawk nesting and foraging.
To help forest managers maintain suitable habitat for Northern Goshawks, the Minnesota Department of Natural Resources (MN DNR) developed the Northern Goshawk Management Considerations (MN DNR 2003), which provide forest management recommendations at three spatial scales: nesting area (30-40 acres [12-16 ha.]), post-fledging area (400-600 acres [162-243 ha.]), and foraging area (12,000-19,000 acres [4756-7689 ha.]). The nesting area provides mature closed-canopy habitat around the nest to protect the incubating female and nestlings/fledglings from predators. The post-fledging area provides closed canopy forest for foraging habitat and to protect fledglings from predators as they learn to hunt and travel increasing distances from the nest. The foraging area provides foraging habitat within the territory for the adults, in which the male and female have separate but overlapping home ranges, and the pair uses the territory year-round (Boal et al. 2003). The Northern Goshawk Management Considerations were developed collaboratively by staff in the divisions of Forestry, Ecological and Water Resources, and Fish and Wildlife. While not prescriptive, the considerations are designed to help inform decision-making by DNR field managers, area teams, landscape teams, subsection teams, and other groups responsible for the management of state-managed forest lands.
The Chippewa and Superior National Forests (U.S. Forest Service 2004a; 2004b) and the Wisconsin Department of Natural Resources also have Northern Goshawk management guidelines that may be of interest.
Conservation Efforts in Minnesota
Various research projects were conducted in Minnesota in the late 1990s and early 2000s to gather information on Northern Goshawk habitat, home range, diet, and productivity and mortality rates (Boal et al. 2003; Boal et al. 2005a; Boal et al. 2005b; Smithers et al. 2005). A synthesis of known information and a research and monitoring plan for Northern Goshawks was developed for the western Great Lakes Region in 2005 (Kennedy and Andersen 2005). In 2003-2005, Northern Goshawk surveys were undertaken in areas with no documented use, to better understand the distribution of the species in northern Minnesota (Hamady et al. 2007). Habitat assessments were undertaken in known goshawk territories to examine habitat patterns at different spatial scales and develop management recommendations (Crozier and Hamady 2006; 2008a). A bioregional monitoring project was conducted in 2008 to establish a baseline estimate of Northern Goshawk occupancy in the western Great Lakes region (Bruggeman et al. 2011). A pilot modeling effort was undertaken to identify suitable areas of contiguous habitat for Northern Goshawks across its distributional range (Hamady et al. 2009); this was followed by another modeling effort to identify suitable locations for managing large patches of mature and older forest based on habitat conditions and current patch management efforts (Crozier and Hamady 2013). Since 2003, an interagency Northern Goshawk monitoring effort has been in place. All known Northern Goshawk territories considered to be occupied are monitored to determine breeding status, nest location, and nest fate. New reports of goshawk breeding areas are confirmed and added to the annual monitoring effort.
Biologists are working to integrate the needs of Northern Goshawks into forest management and planning efforts at different spatial scales. Technical guidance is provided when forest management occurs in known goshawk territories. It is recommended that forest managers implement the Northern Goshawk Management Considerations, with special emphasis on protecting nesting areas. Within long-term forest planning efforts, Northern Goshawk habitat requirements are considered when locating special management areas, such as large mature/old forest patches, and in developing recommendations for retaining older forest and forest interior habitat on the landscape. Currently, efforts are underway to assess key habitat characteristics in Northern Goshawk territories and develop a long-term monitoring plan for the species.
Gaea Crozier (MNDNR), 2018
(Note: all content ©MNDNR)