Northern Goshawk

A regular species throughout the year, including migration and winter. More goshawks migrate through Hawk Ridge in Duluth than anywhere else in North America. The species was rare during the Minnesota Breeding Bird Atlas (MNBBA).

A Holarctic species, in North America the Northern Goshawk is widely distributed across the boreal forest region from Alaska, across Canada, and south into the northern Great Lakes states, New England, and the western United States. It also is found in a small region of northern Mexico. The species is sparsely distributed throughout its breeding range. Figure 1 displays its relative abundance from southern Canada through the United States.

Assigned a Continental Concern Score of 11/20 by Partners in Flight; designated a Sensitive Species on both the Superior and Chippewa National Forests; officially listed as a state Special Concern Species in 2013; also designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources.

Often referred to as a partial migrant. Some birds remain in their breeding areas year-round, while others migrate; the proportion of the population that migrates may depend on winter conditions and prey availability. From 1999 to 2001, 93% of breeding goshawks (26 of 28 birds) radio-tagged in north-central Minnesota appeared to be year-round residents remaining close to the forest stands where they nested (Boal et al. 2003).

Renowned for its swift, aerial pursuit of prey, the goshawk is an opportunistic feeder consuming a variety of birds and small mammals. In Minnesota, Ruffed Grouse, red squirrels, and eastern chipmunks are important prey items (Gullion 1981; Smithers 2001; Smithers et al. 2005).

Large, open platform nest constructed with twigs and lined with bark and fresh green foliage.

On the southern periphery of its breeding range in Minnesota, the Northern Goshawk was not very familiar to the early chroniclers of the state’s bird fauna except as a winter visitor. Hatch (1892) described it as regular during the winter months except when the weather was very mild. He suspected that it bred in the state, but he had no documented evidence. The same year that his report on Minnesota birds was published, his suspicion would prove true. Frank Nutter, a keen observer of birds, published a small note in the journal Oologist describing a goshawk nest he found in Hennepin County, not far from Minneapolis (Nutter 1892)!

Forty years later, Roberts’s (1932) more comprehensive account of the species included Nutter’s record as well as 3 confirmed nesting attempts in Roseau County in 1926 and 1927. Nevertheless, he still believed that the species’ presence was largely confined to the winter season and that it only rarely nested in the state (Roberts 1932). It is more likely that this secretive denizen of the boreal forest had simply gone undetected by early naturalists, who spent far more time in open landscapes of southern and western Minnesota then in the extensively forested landscapes farther north.

By the early 1940s, more reports of goshawks nesting in northern Minnesota began to accumulate. Morse (1942) reported on 3 nesting attempts in Carlton and St. Louis Counties between 1934 and 1942. Additional nesting attempts in St. Louis County were documented by Lakela in 1943 and 1945 and by Olson in 1946 (Lakela 1943, 1945; Olson 1946). When Green and Janssen published their updated account in 1975, they described the Northern Goshawk as a breeding resident in the far northern counties of the state, stretching from eastern Roseau, south to Carlton, and east to Cook. Although Nutter’s 1892 nesting report in Hennepin County remained the only documented nesting record south of this region, they also noted a suspected nesting effort in Morrison County in 1938, just at the southern border of the northern forest region.

In 1981, Gordon Gullion (1981), Minnesota’s renowned expert on Ruffed Grouse, published a small account detailing his observations of nesting sites at the Cloquet Forestry Center in Carlton County dating from 1956 through 1980. His particular interest was the role of goshawk predation on Ruffed Grouse populations. And one year later, David Parmelee (1982) wrote an account of the species’ nesting efforts at Itasca State Park. That same year Johnson (1982) reviewed the status of all Minnesota raptors and reported that since Nutter’s original nesting report in 1892, 61 nests had been reported across northern Minnesota. Despite fluctuations in abundance, he concluded that the Minnesota goshawk population appeared relatively stable. When Janssen (1987) wrote his updated account of the species’ status in 1987, little had changed; he delineated 10 counties where the species was known to have bred since 1970.

Although knowledge of the species’ true breeding status and distribution was increasing, the Northern Goshawk remained an elusive and secretive member of Minnesota’s breeding bird community. The only real opportunity to closely observe this species was during the annual fall migration at Hawk Ridge in Duluth, Minnesota. Each fall an average of a few hundred birds are tallied as they migrate south from their northern Minnesota and Canadian breeding grounds (Hawk Ridge Bird Observatory 2016). This is a relatively small number of birds compared with the thousands of Broad-winged Hawks that pass over the ridge each year. Nevertheless, it is still many more than are observed at the well-known mecca for hawk migration, Hawk Mountain in Pennsylvania, where an average annual count of goshawks is 68 birds (Hawk Mountain 2016).

Interest in the Northern Goshawk began to accelerate in the late 1980s and early 1990s. As timber harvest levels in Minnesota’s northern forests began to rise, so did concern for those species that depended on large tracts of mature forest, including the Northern Goshawk. Numerous field studies were launched that not only examined the Minnesota population in depth but also placed it in context with populations throughout the western Great Lakes region, including Wisconsin, Michigan, and southern Ontario. More intensive field inventories began in 1994 (e.g., Martell et al. 1994; Martell and Dick 1996; Hamady et al. 2003), followed by intensive examinations of effective monitoring techniques (e.g., Roberson et al. 2005; Bruggeman et al. 2011), and studies of foraging habits and nesting habits (e.g., Boal et al. 2001, 2003, 2005, 2006; Smithers 2001; Smithers et al. 2005). Efforts to better understand the origins of migrants that pass through Duluth each fall also were initiated (Hawks et al. 2007).

Due to these studies, knowledge of the Northern Goshawk has expanded tremendously, but the species itself remains rare and elusive. When Hertzel and Janssen (1998) published updated maps of nesting records, they delineated just 8 counties where nesting had been confirmed since 1970. They deleted 3 counties from the map Janssen published in 1987 (Itasca, Crow Wing, and Mahnomen) and added 1 (St. Louis). Unfortunately neither publication includes supporting documentation, so it is unclear why nesting evidence for 3 counties was eliminated. Regardless, records remain rare. Field biologists have combed the northern counties as part of the Minnesota Biological Survey, but they have to date reported only 13 breeding season locations (Minnesota Department of Natural Resources 2016). Because of continuing concerns regarding the Northern Goshawk’s status in the state, it was officially listed as a state Special Concern Species in 2013 (Minnesota Department of Natural Resources 2013).

During the MNBBA, data on goshawks were secured from two primary sources.  First, were data gathered by MNBBA observers who reported 42 Northern Goshawk records from less than 1 percent (37/4,735) of the surveyed atlas blocks and from less than 1 percent (21/2,337) of the priority blocks. Breeding evidence was gathered from just 5 atlas blocks (0.1% of blocks where it was reported) (Table 1 and Figure 3). The birds were observed in 10 of Minnesota’s 87 counties and were confirmed breeding in 3 counties: Lake, St. Louis, and Roseau. The Roseau County record was an addition to the list of confirmed counties published by Hertzel and Janssen in 1998.

Second, were data generously provided by the Minnesota Department of Natural Resources (MNDNR) Northern Goshawk Monitoring Program for the years 2009-2013. At the request of the MNDNR these data were maintained separately and not entered into the MNBBA database. In addition, because a limited number of goshawks are still legally taken for falconry, many publications do not provide detailed information on nesting locations. In keeping with concerns expressed by the MNDNR, the atlas only illustrates the MNBBA and MNDNR goshawk records to the county level rather than to the block level. Figure 2 displays the highest level of breeding evidence by county documented by the combined MNBBA and MNDNR data. The data in Table 1 and Figure 3, however, pertain strictly to the MNBBA data.

Our understanding of the habits and distribution of the goshawk have improved considerably in the past one hundred years. Although Roberts (1932) considered the species to be primarily a winter visitant, it likely always has been a rare, year-round resident of Minnesota’s northern forests. In their comprehensive review of the species, Squires and Reynolds (1997) note that there is few data to document any historical changes in the goshawk’s distribution. They surmise that populations in the western and northern regions of its range have changed very little but speculate that eastern populations may have been negatively impacted by the loss of a major prey item, the Passenger Pigeon, and by the loss of forest lands. As many agricultural lands in New England succeed back to mature forest, eastern populations may recover.

*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.

With a broad distribution throughout North America, the Northern Goshawk has adapted well to a diversity of mature, forested habitats. In the western Great Lakes region, they utilize a variety of mixed deciduous-coniferous forest types. The vegetation composition of the forest is less important than the structural features, which invariably include large trees in a mature or old-growth stand with closed canopies (Figure 4; Squires and Reynolds 1997).

In Minnesota, the birds select large trees in stands with high canopy closure (59.8%–95%) for nesting (Boal et al. 2006). Even in stands dominated by conifers, 80% of nest trees were placed in aspen, followed by birch, white pine, red pine, and red oak (Boal et al. 2001). Nest trees were usually the tallest and largest (i.e., largest dbh) trees available in the nesting area. Stands were also characteristically multistoried with relatively open flight paths available between the canopy and shrub or sapling layer, and between the shrub/sapling layer and the understory. Such structural layering is important for this forest predator that secures its prey by aerial pursuit.

Habitat used for foraging is very similar to that selected for nesting. In general, nesting stands had larger and taller canopy trees and fewer understory trees than foraging habitats (Boal et al. 2005a). Overall, young deciduous stands, lowland conifers, and open areas were used less than predicted based on their availability for both nesting and foraging, while mature forests were used more than predicted based on their availability (Boal et al. 2005a).

Northern Goshawks required large tracts of forests. Individual birds in Minnesota, regardless of their sex, used areas that averaged approximately 2,600 ha. A mated pair, however, used an even larger area. The average size of 11 breeding territories ranged from 5,000 ha to 7,800 ha (Boal et al. 2001).

As noted earlier, studies have suggested that breeding birds in Minnesota (both males and females) remain in the vicinity of their nest site throughout the winter months (Boal et al. 2003). However, year-round residency may be dependent on prey availability.

Partners in Flight recently estimated the North American population of this global species at 210,000 breeding adults. Unfortunately this estimate is derived from federal Breeding Bird Survey data, which is not a robust monitoring tool for such a sparsely distributed, dense-forest species (Rosenberg et al. 2016). The statewide estimate for Minnesota, 1,600 birds, is equally tenuous (Partners in Flight Science Committee 2013).

Since the early 1980s, raptor biologists have experimented with the use of conspecific calls to monitor forest-dependent raptors with reasonably good success (e.g., Fuller and Mosher 1981; Kimmel and Yahner 1990; Kennedy and Stahlecker 1993). A recent study in Minnesota further improved the methodology (Roberson 2001; Roberson et al. 2005). Using these call techniques as a foundation, Hargis and Woodbridge (2006) designed a regional survey approach, arguing that sampling smaller land units for such a widely dispersed species with large habitat requirements was problematic. Bruggemen and his colleagues (2011) implemented the regional survey design proposed by Hargis and Woodbridge across the entire western Great Lakes bioregion, an area that encompassed portions of Minnesota, Wisconsin, and Michigan, in 2008. The results indicated that goshawks occupied 27% of the potential goshawk habitat in the region. To date, this is the only systematic survey conducted for Goshawks in Minnesota and the Great Lakes region. Unfortunately, implementation of a species-specific monitoring protocol across an entire bioregion can be costly for resource-strapped conservation organizations and natural resource agencies. Although the work conducted by Bruggemen et al. (2011) provides an important foundation of monitoring data, lack of funding has prevented further surveys.

The justification prepared for officially listing the Northern Goshawk as a state Special Concern Species provided the best overall assessment of the current status of Minnesota’s Northern goshawk population. Focused survey efforts that began in the 1990s have documented an average of just 29 nesting attempts per year; approximately 79% of these occurred in territories that were occupied the previous year. From 1991 through 2012, a cumulative total of just 130 active territories were identified (Minnesota Department of Natural Resources 2012).

The listing justification reported that nesting success and productivity are lower in Minnesota than in other regions in North America. Among 26 nesting attempts that were closely monitored, 1.14 young fledged per nesting attempt, and 1.85 young fledged per successful nest (Boal et al. 2005b). These rates were similar to two of three studies conducted elsewhere in the western Great Lakes region, and lower than one. Productivity rates throughout the western Great Lakes were lower than the averages reported in 16 studies in western Northern America but still within the reported range of values (Boal et al. 2006).  More recent data from Minnesota document slightly lower reproductive success with an average of 1.05 young per nesting attempt and 1.54 young per successful nest from 2003-2013 (Crozier, pers. comm.).

Fall migration counts conducted at sites throughout the United States provide another source of long-term data on raptor populations that can be used as an index of trends. These counts are now compiled by a consortium of raptor research organizations known as the Raptor Population Index Project (http://rpi-project.org/index.php). Migration counts conducted at Hawk Ridge in Duluth from 1970 to 2013 showed a significant downward decline in the number of Northern Goshawks (Figure 5). These data also clearly illustrated the periodicity in migrant numbers at approximately 10-year intervals. The cycles are believed to be connected with similar cycles in prey abundance, particularly for snowshoe hares and grouse (Squires and Reynolds 1997). An examination of major count sites across the United States and southern Canada revealed that there were no sites where the RPI was increasing, 13 sites where there was no significant trend, 1 with a slight decrease, and 4 with significant declines (Brandes et al. 2017; Crewe et al. 2017). All the sites with declining trends were located in the eastern United States.

Although a number of factors can influence populations and reproductive success in a given year, including inclement weather and low prey availability, habitat degradation and habitat fragmentation are now considered the primary threats to this forest predator. “The availability of large patches of mature forest preferred by the species is in decline regionally due to fragmented land ownership as well as fragmentation of historically large contiguous stands resulting from past and current forest management practices” (Minnesota Department of Natural Resources 2012). Timber harvest in particular can be detrimental to local populations, resulting in nest disturbance, nest destruction, and loss of large tracts of mature forest (Squires and Reynolds 1997). As noted earlier, some birds are still taken for falconry, but the sport is tightly regulated at both the state and federal level to have minimal impact on population trends (Squires and Reynolds 1997).

Although it has a small population size and moderate threats to its breeding population, the Northern Goshawk’s wide distribution has resulted in the assignment of a moderate Continental Concern Score of 11/20 (Rosenberg et al. 2016). A petition filed by several western conservation organizations in 1991 to federally list the western population was declined in 1998 by the U.S. Fish and Wildlife Service. However, the species has been designated a Sensitive Species on many national forests, including the Chippewa and Superior National Forests in Minnesota (U.S. Forest Service 2012).

In Minnesota, the Northern Goshawk was officially listed as a state Special Concern Species in 2013 and has been designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources (2015).

Recognizing the importance of forest management activities for the sustainability of the state’s Northern Goshawk population, in 2003 the Minnesota Department of Natural Resources developed a series of Northern Goshawk Management Considerations to help guide and inform forest landscape planning initiatives on state forest lands (Minnesota Department of Natural Resources 2003). These considerations acknowledged the importance of maintaining a forest landscape that includes a mosaic of different forest conditions, including a range of patch sizes, forest types, and stand ages, to provide sufficient habitat for goshawks. Specific habitat considerations are outlined for breeding territories, nest areas, and post-fledging areas that address the need for large tracts of mature forest in and near known territories.

Because more than 40% of the goshawk’s range occurs in the boreal forests of Canada, attention to forest conservation and management issues in Canada is extremely important. Although the impacts of climate change have not been closely examined, the species has been tentatively ranked as having a low vulnerability to any changes resulting from warming temperatures (North American Bird Conservation Initiative 2010).

The species’ apparent declining population trend needs to be closely watched in the coming years. The Northern Goshawk is a conservation concern due to its vulnerability to certain forest management practices and predicted declines in habitat availability in Minnesota. The state, however, has a long-standing tradition of integrated, landscape-scale forest management which may benefit the species. This kind of management is coordinated across ownership boundaries and strives to maintain a diverse landscape for all forest-dependent species.