Northern Goshawk Forest Type Preference in the Chippewa National Forest Travis W. Ludwig Department of Resource Analysis, Saint Mary’s University of MN, Winona, MN 55987 Keywords: Goshawk, Accipiter gentilis, GIS, forest stands, Chippewa National Forest, minimal convex polygons, quaking aspen Abstract The Chippewa National Forest has large expanses of land that are densely forested and largely uninhabited providing excellent habitat for Northern Goshawk (Accipiter gentiles). The Chippewa National Forest is currently updating its forest management plan and one of the issues is the importance of goshawk habitat. The goshawk is a listed Sensitive Species in the Eastern Region for the U.S. Forest Service. This study used a geographic information system to assess which forest types are important as goshawk habitat. Since limited knowledge exists concerning goshawk habitat, three habitat estimations (minimal convex polygons, Kernel 95% and Forage Buffer) were used to determine which forest stands occur within goshawk utilization areas. While quaking aspen plays a vital role in goshawk habitat in the Chippewa National Forest, goshawks there are opportunistic and take advantage of many other forest types. Introduction The Chippewa National Forest, hereafter called Chippewa NF, encompasses 1.6 million acres. Of this, 666,325 acres are managed by the USDA Forest Service. The forest consists of aspen, birch, pine, balsam fir, and maple species. The Chippewa NF contains approximately 1300 lakes, 900 miles of rivers and streams, and 400,000 acres of wetlands. The Chippewa NF is the largest national forest east of the Mississippi (Chippewa National Forest Website, 2002). The Chippewa NF is located in northern Minnesota between the cities of Grand Rapids to the east and Bemidji to the west (Figure 1). The Chippewa NF supervisor’s office is located in Cass Figure 1. Location of the Chippewa Lake, Minnesota. National Forest within Minnesota The Northern Goshawk (Accipiter gentiles) is the largest of three North American accipiters. 1 Accipiters are hawks characterized with species, the bird takes flight and pursues short rounded wings and long tails. the animal (Palmer 1988) in short flight These traits are useful because these (Kenward 1982). In general, foraging species prefer wooded habitat. The other individuals travel through the forest in a accipiters are the Cooper’s hawk and the series of short flights, with brief periods Sharp-Shinned hawk (Squires and of ‘prey searching’ from elevated Reynolds 1997). Goshawks are well hunting perches (short duration ‘sit and known for aggressive pursuit of prey in wait’ predatory movements) (Squires thick forest conditions. and Reynolds 1997). Goshawks hunt by The goshawk is a hawk with flying rapidly along forest edges, across broad wings and a long, rounded tail. openings and through dense vegetation These morphological adaptations allow to surprise prey (Johnsgard 1990); they it to move efficiently through forest may also attack prey in mid-air stands that are much too dense for its (Kenward 1982). They may stalk prey open-forest avian counterparts, on foot, using the surroundings to hide providing it with a competitive from their prey (Bergstrom 1985, advantage (Lilieholm, Kessler, and Backstrom 1991). Prey that may be Merrill 1993). Females are larger than hunted and consumed by goshawks in males: males average 21 inches, females Minnesota are: gray and red squirrels, average 24 inches in length (Wood chipmunks, rabbits and hares, ruffed 1938). The wing span of the male is grouse, pheasants, woodpeckers, blue approximately 40 inches and the female jays, crows, flickers, robins, and wingspan is greater by 2 inches sapsuckers. Occasionally goshawks feed (Wheeler and Clark 1995). The weight on carrion (Squires and Reynolds 1997). of goshawk males ranges from 631 g to In the United States, goshawks 1099 g and the much heavier female hunt in diverse areas. They have from 860 g to 1364 g. Goshawks are adapted to pursuing prey in forests. heavy bodied with dark blue-gray backs, Their broad wings with elongated wing black crowns, pale underparts finely tips are also adapted for ambushing prey barred with grey and conspicuous white in open habitats (Wattel 1973). Much eyebrows. Young goshawks are similar remains to be learned about actual in pattern but are brown above and foraging preferences for goshawks. streaked below (Bull and Farrand, Jr. Though acquired prey may change with 1977). the seasons, preferred hunting habitat Goshawks are opportunistic has been shown to remain constant predators and prey on a wide variety of throughout the year (Widen 1989). The animals, depending on region, season presence of tall trees and snags from and availability (Squires and Reynolds which the search for food begins is 1997). The goshawk’s method of essential. Research has shown that hunting involves the use of tall trees as stands become suitable as goshawk perches from which it surveys the lower habitat once the trees have reached an branches and forest floor for small birds average height of 25 m (Lilieholm, and mammals. It relies on substantial Kessler, and Merrill 1993), though trees canopy closure to conceal it from its of 16 m will often suffice. Stands with prey (Reynolds and Meslow 1984). trees of less than 8 m height are Upon observation of a suitable prey generally avoided (Schaffer 1995). In a 2 study in northern Arizona, foraging sites tree bark (Saunders 1982). Water is were not observed to be selected on the usually present near nests but is not a basis of prey abundance but were key requirement (Squires and Reynolds selected by goshawks on the basis of 1997). Hawks bathe and wade in water forests with greater canopy closure but any benefit to nesting is unknown (Beier and Drennan 1997). In contrast, a (Brown and Amadon 1968). The Nevada study showed that goshawks requirements for foraging habitat are not foraged in open sagebrush for ground as stringent as those for nesting. It is squirrels (Younk and Bechard 1992). essential that prey is both available and Small forest openings seem to accessible and that tall perch trees are have a negative impact on the nesting present (Benson 1979). efficiency of goshawks but these gaps This study examines what, if any, are important to prey (Squires and forest types are preferred by goshawks Reynolds 1997). In one study in for foraging in the Chippewa NF and Pennsylvania, goshawks were observed what importance the dominant forest to avoid nesting near light traffic dirt type has on the goshawk habitat. Human roads but often nested near woodland activity is the greatest threat to goshawk trails (Kimmel and Yahner 1994). In survival. The best way to protect the Oregon, goshawks were observed to nest goshawk is to keep researching and near forest openings and trails (Squires accumulating data to better understand and Reynolds 1997). the species. This project attempts to Territorial goshawks will attack provide more information about and kill other raptors, and they may even goshawk habitat so that conservation kill other goshawks. Goshawks are planners and wildlife managers can extremely aggressive during nesting and protect this valuable raptor habitat. have been known to attack humans if threatened. Goshawks often patrol Data Collection nesting boundaries by soaring around them high enough so other birds will Data for this study were acquired from recognize the boundaries (Squires and John Rickers, GIS Coordinator of the Reynolds 1997). Chippewa NF. All forest stand data Female goshawks are often were created and maintained by the observed repairing nests early in the Chippewa NF. All goshawk telemetry season, as they select suitable nest sites and habitat data were created by the (Schnell 1958). Nests are built in a Minnesota Cooperative Fish and variety of trees. Deciduous trees may be Wildlife Research Unit. preferred in the Midwest for nest choice, but insufficient data exist to validate this Stand Data observation. Goshawks nest in the largest tree in the stand and are often in The forest stand layer graphically the lower third of the tree. The size and displays and describes natural or structure of nest trees may be more artificial created vegetation which important than the species (Squires and exhibits sufficient homogeneity to make Reynolds 1997). Nests are bowl-shaped it distinguishable from surrounding and are constructed of thin sticks, lined areas. ‘Stands’ are both forested and with greenery (moss, leaves etc.) and nonforested. The data were created from 3 1:15,840 data sources including rectfied A few females were radio- base photography, and district tracked because they sometimes will compartment maps. This data also meets forage during the nestling stage (Boal national map accuracy standards. The and Mannan 1996). forest stand data file was an ESRI Radio-located points were ArcInfo© coverage converted to a plotted on DOQs by hand, and UTM shapefile in ArcView©. coordinates were calculated for each point. The researchers used the Goshawk Data Movement 1.1 ArcView Spatial Analyst Extension to create GIS coverages. The The Minnesota Cooperative Fish and home range sizes were estimated with Wildlife Unit produced the goshawk the minimum convex polygon (MCP) data for this study. Goshawks were method (Figure 2). This is like stretching captured using traps, lured by live or a rubber band around the located points. plastic replicas of a great horned owl. Figure 2 shows that ranges were Once captured, the goshawks were fitted calculated for female and male home with radio transmitters. Researchers ranges and a pooled home range, which then tracked the goshawks for one to two will be used in this study. breeding seasons, depending on the The Fixed Kernel method of mortality of the goshawks during the home range estimation using a 95% study. Males were targeted because they contour (K95) is shown in figure 3. This do most of the foraging from courtship method is best described as a buffer that through at least the early nestling stage is created to incorporate 95% of all (Squires and Reynolds 1997) and often located points and the probability of through the fledgling dependency period other points where they may be located.