NORTHERN GOSHAWK REPRODUCTIVE HABITAT

HABITAT SUITABILITY INDEX MODEL VERSION 3

Last Modified: 21 October 1999

Warren Schaffer, 5 Gillivray Ave., Toronto, Ontario. M5M 2X9. Barbara Beck, Department of Renewable Resources, University of Alberta, Edmonton, Alberta. T6G 2H1. James Beck, Department of Renewable Resources, University of Alberta, Edmonton, Alberta. T6G 2H1. Richard Bonar1, Weldwood of Canada, 760 Switzer Drive, Hinton, Alberta. T7V 1V7. Laurie Hunt, Environmental Training Centre, 1176 Switzer Drive, Hinton, Alberta, T7V 1V3.

1. INTRODUCTION Habitat Suitability Index (HSI) models predict the suitability of habitat for a species based on an assessment of habitat attributes such as habitat structure, habitat type and spatial arrangements between habitat features. This HSI model for the northern goshawk (Accipiter gentilis atricapillus) applies to habitats of the Foothills Model Forest (FMF) in west-central Alberta. The intended use is to predict habitat suitability at landscape scales and over long-time periods. The model will be used to determine potential changes in northern goshawk habitat area and carrying capacity throughout an entire forest management cycle (200 years). This model was developed based on original data gathered by the first author as part of a M.Sc. degree at the University of Alberta, literature review, and expert opinion.

2. SPECIES DESCRIPTION AND DISTRIBUTION The northern goshawk is the largest North American member of the genus Accipiter, which includes sharp-shinned hawks (A. striatus) and Cooper’s hawks (A. cooperii). Northern goshawks are the size of a common raven (Corvus corax) ( Jones 1979). They have long tails (> 30 cm) and relatively short rounded wings (adult male wing length: 30-33 cm, adult female wing length: 33-37 cm; Jones 1979, Godfrey 1986). Northern goshawks are known for their rapid flight over short distances and their pursuit of prey into dense cover (Jones 1979, Johnsgard 1990). A reverse sexual dimorphism is exhibited with an average adult male mass of 0.9 kg and an average female mass of 1.1 kg (P. Duncan, and D. A. Kirk. Status report on the northern goshawk Accipiter gentilis in Canada, unpublished manuscript, 1994).

The breeding range extends from north-western Alaska, through to Labrador and Newfoundland, south to California, across the continental U.S. to Maryland and into Mexico. The winter range extends from western and central Alaska and British Columbia and southern Newfoundland to southern California, Mexico, Tennessee and the Virginias (Jones 1979). In Alberta, the northern goshawk breeds in northern and western Alberta and is most common in the Boreal, Foothills, and Rocky Mountain regions (Semenchuk 1992). Northern goshawks in Alberta are considered a sensitive species that are not currently at risk but may require special management (Wildlife Management Division 1996).

In years with sufficient availability of prey, northern goshawks are year-round residents in the northern parts of their range (including the boreal forests of west-central Alberta; P. Duncan, and D. A. Kirk. Status report on the northern goshawk Accipiter gentilis in Canada, unpublished manuscript, 1994). Large southward migrations of northern goshawk populations occur approximately every 10 years (Keith et al. 1977, Mueller et al. 1977). Other movements in response to low prey numbers include the movement from subalpine forests to low elevation woodlands, riparian areas, and scrubland during winter (Reynolds et al. 1992).

NOGO-1

1 Contact Address

Northern goshawk breeding can be disturbed by human-related activities. Logging and vehicular traffic in the immediate vicinity of the nest can reduce the attentiveness of adult females (Grier and Fyfe 1988, Richardson and Miller 1997). Changes to nesting (Reynolds et al. 1982, Moore and Henny 1983, Kennedy 1988, McCarthy et al. 1989, Reynolds 1989, Crocker-Bedford 1990, Bosakowski and Speiser 1994) or foraging (Kirk 1995, Beier and Drennan 1997) habitats can make these habitats unsuitable.

3. FOOD Northern goshawks require 120-150 grams of food per day or about 10-15% of their body weight (Brown and Amadon 1968). From birth to fledging, two nestling northern goshawks require about 13 kg of food. Depending on the size of prey taken, adults have to capture between 100-250 prey items to achieve this mass (Schnell 1958).

Northern goshawk prey in west-central Alberta was mainly small mammals and birds (Table 1; Schaffer 1998) which is consistent with other investigations (Henderson 1924, Meng 1959, Storer 1966, Palmer 1988, Widen 1989, Bull and Hohmann 1994, Doyle and Smith 1994). Throughout the North American range, mammals accounted for 86-94% (by biomass; Table 2), and birds accounted for 6-13% of the diet (by biomass; Table 2).

Table 1. Diet of northern goshawks in west-central Alberta as determined by direct observation of northern goshawk feeding behaviour (Schaffer 1998). Frequency of Prey Species Diet Composition

Prey Species Direct Observation Percent of Total Biomass

MAMMALS 25 88.6

Snowshoe Hare (Lepus americanus) 6 63.97

Red Squirrel (Tamiasciurus hudsonicus) 13 20.94

Bushy-tailed Woodrat (Neotoma cinerea) 1 2.49

Meadow Vole (Microtus pennsylvanicus) 3 0.69

Unidentified Microtine 2 0.46

BIRDS 8 11.4

Ruffed Grouse (Bonasa umbellus) 1 4.28

Pileated Woodpecker (Dryocopus pileatus) 2 4.26

Northern Flicker (Colaptes auratus) 2 1.65

Three-toed Woodpecker (Picoides tridactylus) 1 0.49

Gray Jay (Perisoreus canadensis) 1 0.53

Hermit Thrush (Catharus guttatus) 1 0.23

TOTAL PREY 33 100

Table 2. Percent composition of birds and mammals (by biomass) of northern goshawk diet. Location Mammals Birds Source

Alaska 90 10 Zachel 19851

Alberta 89 11 Schaffer 19982

Arizona 94 6 Boal and Mannan 19942

Yukon 86 15 Doyle and Smith 19943 1 - Pellet analysis. 3 - Prey remain analysis. 2 - Direct observation.

NOGO-2

4. COVER Cover for nesting and foraging is typically in mature to old deciduous-dominated mixedwood stands, with well-developed canopies and open understories (Shuster 1980, Reynolds et al. 1982, Moore and Henny 1983, Reynolds et al. 1992, Schaffer 1998). Nest trees within these areas are generally large diameter/tall deciduous species with a suitable nest holding location and high surrounding cover for protection against extreme weather and predation.

4.1 FORAGING COVER

Open understory conditions beneath a dense canopy offer a good flight corridor for foraging (Reynolds et al. 1982, Hayward and Escano 1989). Stands with open canopies tend to have dense understories which may diminish the success of foraging due to reduced visibility, restricted flight access to prey, and greater escape cover for prey (Widen 1989; P. Duncan, and D. A. Kirk. Status report on the northern goshawk Accipiter gentilis in Canada, unpublished manuscript, 1994). Northern goshawks have a fairly large body size and wing span, and are not suited for hunting in dense immature forests (Reynolds et al. 1992; P. Duncan, and D. A. Kirk. Status report on the northern goshawk Accipiter gentilis in Canada, unpublished manuscript, 1994). Prey use data gathered in west-central Alberta revealed that prey of northern goshawks were usually in the lower forest strata (Table 3; Schaffer 1998). Mature forest seems to represent the best compromise between maneuverability and attack, and concealment of its approach (Widen 1989). Trees that predominate older stands are tall with large diameters. Tree breakage results in standing and fallen woody material, which provides perching and plucking posts for northern goshawks (Schnell 1958, Reynolds et al. 1992).

Table 3. Diet of northern goshawks on the western study area, as detected by the direct sampling technique, according to their foraging zone (Schaffer 1998).

Vegetation Zonea Biomass of Prey (%)

(1) Ground-Shrub 67.84

(2) Shrub-Canopy 0

(3) Canopy 4.75

(4) Aerial 0

(5) Generalist 27.41

TOTAL 100.00 a - vegetation categories from Reynolds and Meslow (1984), based on information found in Banfield (1974), Kaufman (1996).

4.2 NESTING COVER

Northern goshawk nesting areas in central Alberta exhibited a variety of attributes (i.e. multiple canopy layers, canopy gaps, large standing and fallen dead trees, multiple ages of trees; Schaffer 1998) which characterize the mature seral stage of deciduous-dominated mixedwood forest (Perala 1990, Mehl 1992, Moir 1992). Other North American studies have also concluded that older seral stages are important for northern goshawk nesting (Reynolds et al. 1982, Moore and Henny 1983, Speiser and Bosakowski 1987, Kennedy 1988, Hayward and Escano 1989, Squires and Ruggiero 1996). Overstory vegetation in nesting areas in central Alberta was dominated by trembling aspen (Populus tremuloides), balsam poplar (Populus balsamifera), and white birch (Betula papyrifera), but also had some conifers (white spruce Picea glauca, lodgepole pine Pinus contorta, black spruce Picea mariana). Coniferous trees may be an important component of the nesting stand because they protect the nest from extreme conditions early in the nesting season (Moore and Henny 1983, Speiser and Bosakowski 1987, Schaffer 1998). Across North America, northern goshawks preferred mixedwood areas for nesting, while deciduous areas were of secondary importance, and pure conifer forests were the least used habitat (Apfelbaum and Seelbach 1983).

Nesting stands with a dense tree canopy closure (range 59.8-94.0%; Table 4, adapted from Siders and Kennedy 1994) have a mild and stable microclimate (Speiser and Bosakowski 1987, Crocker-Bedford and Chaney 1988, Reynolds et al. 1992). Incidence of nestling predation by great horned owls (Bubo virginianus), red-tailed hawks (Buteo jamaicensis), and fishers (Martes pennanti) decreases in closed canopy stands (Reynolds et al. 1992). Open understory conditions provide good access to the nest (Reynolds et al. 1982, Hayward and Escano 1989). Optimum

NOGO-3

closure should be at least 79% (the average for northern goshawk nesting areas), while moderate habitat is at 72% and poor habitat is ≤ 60% canopy closure (Crocker-Bedford and Chaney 1988).

Table 4. Nest stand average canopy closure (%) reported in various studies. Location Canopy Closure (%) Sample Size Method of Measurement Source

Alberta, central 77.4 17 Spherical densiometer Schaffer (1998)

Arizona 76.0 36 Spherical densiometer Crocker-Bedford and Chaney (1988)

California, N.W. 94.0 10 Spherical densiometer Hall (1984)

Montana - Idaho 80.0 17 Spherical densiometer Hayward and Escano (1989)

New Mexico 65.7 42 Spherical densiometer Siders and Kennedy (unpubl data)

New York - New Jersey 90.0 16 Ocular sighting tube Bosakowski et al. (1992)

Oregon, E. 59.8 7 Ocular estimate Reynolds et al. (1982)

Wyoming 66.7 39 Line-intercept sampling Squires and Ruggiero (1996)

Mature trees in nesting and foraging areas are more likely to blow down or break which results in a discontinuous canopy. This may be important for the nest flyway, or to act as a landmark for adults returning to the nest area (Reynolds et al. 1982, Hall 1984, Speiser and Bosakowski 1987).

4.3 NEST TREE CHARACTERICS

A minimum nest height threshold may occur (Schnell 1958, Speiser and Bosakowski 1987). The lowest reported height was 5 m (Jones 1979, Godfrey 1986), however, most nests were substantially higher, ranging from 8-25 m (Beebe 1974, Call 1978, Jones 1979, Reynolds et al. 1982, Godfrey 1986). Differences exist among geographic areas where different species grow, and among species in the same area. For example, in Colorado the height in trembling aspen was 12-15 m and in ponderosa pine (Pinus ponderosa) and lodgepole pine the nests were 8-12 m high (Shuster 1980).

Data collected in central Alberta suggest that large Populus trees are used almost exclusively for nesting (N = 45; 37 nests in trembling aspen, 5 in balsam poplar, 1 in white birch, 1 in lodgepole pine, 1 in white spruce; Schaffer 1998 from data contributed by R. Cromie, A. de Groot, E. T. Jones, C. McCallum, J. Moore, D. Mushtuk, B. Olsen, E. Pletz, T. Roper, C. Spytz, H. Wollis). The mean diameter at breast height (dbh at 1.3 m) of nest trees was 30 cm (range 16-46 cm, n = 25), and the dbh of overstory vegetation in the nest stand was 15-25 cm. The mean height of nest trees was 22 m (range 14-28 m, n = 25). The mean nest height was 15 m (range 11-22 m). Nests were typically placed at the base of the canopy in a primary branch fork (19 of 25 nests), but were also situated within the crown (6 of 25 nests). Nests were also positioned on whorls of branches (mean number of supporting branches = 4; mean nest height as a percent of nest tree height = 68%; Schaffer 1998). Northern goshawks have been observed to have a stronger preference than other hawks for trees with 3-4 upturned branches in which to firmly place their nest (R. Cromie, raptor bander, personal communication). Dead branches in the lower crowns of trees may be important for nest material (Reynolds et al. 1982). A nest positioned at the base of the canopy may benefit northern goshawk reproduction because the nest is more accessible for adults in nest defense or feeding activities (Reynolds et al. 1982, Moore and Henny 1983, Hayward and Escano 1983, Hall 1984, Speiser and Bosakowski 1987). This nest position also affords the northern goshawk the best view of the forest surrounding the nest tree (Hall 1984, Janes 1985).

5. REPRODUCTION The sequence of events in the progress of northern goshawk breeding and brood-raising at a new nesting area is: pair formation, nest construction, copulation, egg-laying, incubation, feeding of young (nestling period), initial fledging period, transitional fledgling-dependency period, and finally, fledgling independence (Jones 1979). The nesting territory is advertised by one or both of the residents by an aerial display (Johnsgard 1990). Pair formation, nest construction, and copulation takes 2-4 weeks and egg-laying follows (Jones 1979, DeStephano et al. 1994, Reynolds et al. 1994). The incubation period typically lasts 30-32 days and the nestling period generally lasts 34-37 days (Jones 1979, Bull and Hohmann 1994, DeStephano et al. 1994, Reynolds et al. 1994). The fledgling-dependency period lasts an additional 42-60 days (Jones 1979, Kennedy et al. 1994). Once the fledgling-

NOGO-4

dependency period is completed, all family members typically leave the nesting area and exhibit localized wanderings (even in resident populations; Jones 1979, Hargis et al. 1994, Kennedy et al. 1994).

Northern goshawks in central Alberta settle on territories in the first week of March, and remain in the post-fledging family area around the nest until late August (R. Cromie, A. de Groot, E. T. Jones, J. Moore, E. Pletz, T. Roper, personal communications, W. Schaffer, unpublished data, Reynolds and Wight 1978, Jones 1979, P. Duncan, and D. A. Kirk. Status report on the northern goshawk Accipiter gentilis in Canada, unpublished manuscript, 1994). The northern goshawk breeding season is timed so that newly fledged chicks can use newly fledged passerine birds as a food source (Jones 1979).

6. HABITAT AREA There are 3 different areas of importance for northern goshawk habitat - the nesting area, post-fledging family area, and home range (Reynolds et al. 1992). The nest area contains the nest and vegetation in its immediate vicinity, and represents the area of most intense use by northern goshawks during the reproductive season (Reynolds et al. 1992). The nest area is actively defended by the adults against other raptors, including other northern goshawks during the nesting season (Squires and Ruggiero 1997). Northern goshawks exhibit strong site fidelity and may use the same nest for consecutive years, but typically alternate between ≥ 2 nests within nest areas (Reynolds and Wight 1978). The post-fledging family area is used after the chicks have left the nest and have started to become independent. The composition of the post-fledging family area has a direct influence on recruitment, because of its importance to fledged young (P. Duncan, and D. A. Kirk. Status report on the northern goshawk Accipiter gentilis in Canada, unpublished manuscript, 1994). Northern goshawk mortality is typically caused by starvation due to lack of success gathering food or dealing with changes in abundance or diversity of local food sources (Snyder and Wiley 1976). The home range is the area used by the adults for foraging during the year (Reynolds et al. 1992). There is no data to suggest that northern goshawks defend all of their home range. Core areas within the home range (including the nest area, and important foraging zones) are defended (Squires and Ruggiero 1997).

There is considerable variation in the area recommended for northern goshawk nest area management in North America (8-80 ha: Table 5). Until more complete information is available, a minimum management area for northern goshawk nest sites in central Alberta will be set at 12.0 hectares (radius 200 metres).

Alternate nesting areas for northern goshawks in the vicinity of the current nesting area are an important element of habitat suitability (Reynolds 1983, Crocker-Bedford and Chaney 1988, Woodbridge and Detrich 1994). In northern California, northern goshawk territories typically contained 1-5 different nesting stands (Woodbridge and Detrich 1994). These stands ranged from 4-12 ha in size (n = 71) and were, on average, 273 m apart. Mean distance between alternate nests was 266 m (n = 17; Reynolds et al. 1994). A number of possible management techniques have been proposed to ensure adequate provision for alternate nest sites for northern goshawks within their home ranges. Maintaining 6 potential nesting areas within each home range has been suggested (Reynolds et al. 1992). Others have suggested that optimum nesting habitat should have at least 3 potential nesting stands within 1 km of each other; while fair nesting habitat consists of 2 nesting stands, and poor nesting habitat has only 1 possible stand (Crocker-Bedford and Chaney 1988).

In North America, reproductive season home ranges vary from 1,530-4,000 ha (Table 6). Northern goshawk home range in the boreal foothills of Alberta has been estimated to be 5,000 hectares (D.C. Crocker-Bedford, personal communication). The northern goshawk post-fledging family area has been estimated at 170 hectares (Kennedy et al. 1994).

Table 5. Recommended area for provision of habitat for northern goshawk nest sites.

Location Area (ha) Radius (m) Source

NOGO-5

United States 50.0 - 80.0 400.0-500.0 Jones 1979

Oregon 8.0 160.0 Reynolds et al. 1982

western United Sates 8.0 160.0 Reynolds 1983

New Mexico 20.0 250.0 Kennedy 1988

Arizona >8.0 >160.0 Crocker-Bedford and Chaney 1988

New Hampshire 50.0 400.0 Lanier and Foss 1989

California 50.0 400.0 McCarthy et al. 1989

southwestern United States 12.0 200.0 Reynolds et al. 1992

New Mexico 10.0 180.0 Kennedy et al. 1994

Table 6. Mean northern goshawk reproductive season home range areas. Location Area (ha) Method Source

New Mexico, N. Central 2105 95% harmonic mean radio-telemetry Kennedy 1990

California, N. 1922 95% harmonic mean radio-telemetry Austin 1993

Arizona, N. 1530 95% harmonic mean radio-telemetry Bright-Smith and Mannan 1994

California, E. 2400 adaptive kernel method (95% contour) Hargis et al. 1994

Yukon, S.W. 4000 95% outer convex polygons Doyle and Smith 1994

6.1. HABITAT SELECTION

Habitat selection by Accipiters operates in a hierarchical fashion including home range selection from the landscape, foraging area and nesting area selection within the home range, and nest tree selection within the nest area (Reynolds et al. 1992). Accipiters select a home range with adequate food supplies and this is probably a function of the habitat distributions in the local landscape (Jones 1979, Kennedy et al. 1994). Nest areas are typically close to foraging areas, and have prey available on site for the critical fledgling-dependency period. Other factors influencing nest site selection are historic nesting success, vegetation at the site, and similarity to natal habitat (Speiser and Bosakowski 1987, Kennedy 1988). Nest tree selection is likely based on tree size and architecture (arrangement of branches) (Squires and Ruggiero 1996). Foraging areas within the home range consist of both prey source areas and prey utilization zones (Widen 1989, Hargis et al. 1994). Optimum northern goshawk foraging habitat is characterized by an interspersion of areas with high prey abundance (young seral forests: Reynolds et al. 1992, Hargis et al. 1994) and areas that are favourable for northern goshawk foraging (mature and old seral forest: Crocker-Bedford 1990, Bright-Smith and Mannan 1994).

7. HSI MODEL 7.1 MODEL APPLICABILITY

Species: Northern Goshawk (Accipiter gentilis atricapillus).

Habitat Evaluated: Reproductive habitat (nesting, foraging and post-fledging areas) .

Geographic area: This model is applicable to west-central Alberta.

Season: The reproductive season lasts from early spring (early March) to late summer (late August).

Cover types: This model applies to all forest and non-forest habitat areas of the Lower and Upper Foothills, Montane and Subalpine Natural Subregions (Beckingham et al. 1996) since suitability is determined from structural characteristics within stands rather than classified forest stands directly. The model should also be broadly applicable to other habitat areas dominated by vegetation similar to that in this region, including pure deciduous, mixedwood and pure coniferous forest types, as well as wetland and riparian forests, meadows, shrublands, and areas regenerating after forest harvesting.

NOGO-6

Minimum Habitat Area: Minimum habitat area is defined as the minimum amount of contiguous habitat to which the model will be applied. It is assumed that a minimum of 12 hectares of contiguous habitat is a reasonable area of habitat for northern goshawk nest sites. Thus, any areas less than 12 ha in size will receive no suitability value for nesting There is no minimum area for foraging.

Model Output: The model will produce Habitat Units (HU) for food and cover for each classified stand based on HSI value and stand area. HU are calculated by multiplying the HSI score with the area in hectares. The performance measure for the model is potential carrying capacity (northern goshawk pairs per ha). Model output (HU) should be correlated to estimates of carrying capacity.

Carrying Capacity (Northern goshawk pairs per ha where HSI = 1.0): Northern goshawk home range sizes have been used to aid in this estimation. A home range area of 5000 ha has been suggested for this area. However, that size is reflective of a mixture of optimal and semi-optimal habitat and perhaps 1000 ha of optimal feeding habitat would be a more appropriate value. This would suggest that 0.001 pairs per ha would be possible.

Verification Level: The reliability of this model has not been evaluated against local data. The verification level is 4: local data used to develop model but model predictions have not been tested.

Application: This HSI model is designed to assess habitat suitability for relatively large forest landscapes using generalized species-habitat relationships and stand-level vegetation inventory. Its purpose is to predict relative changes in northern goshawk habitat supply at the landscape level over long time periods (200 years), for integration with forest management planning. The model is not designed to provide accurate prediction of suitability or use at the stand level. Approximate population size can be calculated by assuming linear habitat-population relationships, but the model is not designed to provide accurate population density estimates. Any attempt to use the model in a different geographic area or for other than the intended purpose should be accompanied by model testing procedures, verification analysis, and other modifications to meet specific objectives.

7.2 MODEL DESCRIPTION

The northern goshawk HSI model assumes that reproductive habitat is the limiting factor on the population of northern goshawks in central Alberta.

7.2.1 Habitat Variables and HSI Components

A. Nesting Habitat

Northern goshawks require a large tree capable of supporting a stick nest, which in central Alberta is usually a deciduous (Populus) tree. Large aspen trees are the preferred nesting tree because they are usually open branched below the canopy and often have a number of branches forming a cradle near the top. Tree canopy height (which is used to define HSI component S1) is used to predict the availability of large nest trees. Habitat surrounding the nest must have high canopy closure for protection against predation and extreme weather and is incorporated into the model as S2. Nesting habitat is best within mixedwood stands, since these have conifers for protection and deciduous trees for alternative nesting and roosting sites, and they are likely to provide a nearby source of food for the young. To include mixedwood stands in the prediction of nesting habitat suitability, S3 is defined using deciduous percent composition. Northern goshawks generally do not nest near sources of disturbance or harassment, and thus avoid areas near human activities. To account for this, S4 has been defined by the distance to nearest settlement, road, or human activity (Table 7).

B. Foraging Habitat

The best foraging for northern goshawks occurs in stands with high structural and tree species diversity. These conditions are determined in the model by percent deciduous tree composition, tree canopy closure, and tree canopy height, which define HSI components S5, S6 and S7 (Table 7). The deciduous composition variable in effect limits the model to give the best suitability values in mixedwood stands. Pure conifer or deciduous stands do not support the diversity of prey species on which the northern goshawk depends. Northern goshawks can hunt under most canopy conditions but avoid stands of very high density where effective hunting is difficult. Areas with low tree canopy closure are avoided since the protective cover of trees is necessary for concealed hunting. Tree height is used mainly as an index of forest development. Taller, older stands have a diversity of structural features such as snags, downed wood, mixed canopy layers, and varied ground cover, all of which promote prey abundance, diversity, and availability to foraging northern goshawks.

NOGO-7

Table 7. Relationship between habitat variables and life requisites for the northern goshawk HSI model.

HSI Component

Life Requisite

Habitat Variable Habitat Variable Definition

S1 Nest Tree Tree Canopy Height (m)

Mean top height of 100 trees per hectare with the largest diameter at breast height (dbh).

S2 Nesting Cover

Tree Canopy Closure (%)

Percent of ground covered by a vertical projection of tree crown areas onto the ground. Includes all trees ≥ 8 cm dbh.

S3 Nesting Cover

Deciduous in Tree Canopy (%)

Percent composition of aspen, balsam poplar and birch species in the tree canopy.

S4 Habitat Effectiveness

Distance to Human Disturbance (m)

Human disturbance includes roads, camps, active well sites, or gas plants, settlements, recreation areas, etc.

S5 Foraging Cover

Deciduous in Tree Canopy (%)

Percent composition of aspen, balsam poplar and birch species in the tree canopy.

S6 Foraging Cover

Tree Canopy Closure (%)

Percent of ground area covered by a vertical projection of tree crown areas onto the ground. Includes all trees ≥ 8 cm dbh.

S7 Foraging Cover

Tree Canopy Height (m)

Mean top height of 100 trees per hectare with the largest diameter at breast height (dbh).

7.2.2 Graphical HSI Component Relationships

A. Nesting

S1 A nest stand must have a mean height > 12 m. S1 reaches a value of 1 when the stand height ≥ 20 m (Figure 1a). These values ensure that the forest is old enough to provide trees of suitable size for nesting. In Alberta, mean nest tree height ranged from 14-28 m and nests have been reported in aspen trees as small as 12 m height; thus there will be some trees large enough to support a nest even at a mean height of 12-19 m.

S2 Stands ≤ 30% canopy closure are considered to be too open for nesting habitat and are given a value of 0. Percent tree canopy closure is optimal (S2 = 1) when it is ≥ 50%. Between 30 and 50% the value rises linearly (Figure 1b).

S3 Pure conifer stands (represented as 0% deciduous) and pure deciduous stands are less suitable than mixedwood stands for nesting habitat. At 0% deciduous S3 = 0.05. Suitability rises to 1 at 10% deciduous, and stays at 1 until 90% is reached. The value then drops again, this time to 0.5 at 100% deciduous composition (Figure 1c). Pure deciduous is not considered to be as unsuitable as pure conifer, and both are considered to provide some opportunity for nesting habitat.

S4 Nesting habitat must be farther than 50 m from human disturbance such as roads, camps, active well sites, or gas plants. At 50 m the model predicts that habitat can be fully suitable (Figure 1d).

B. Foraging

S5 Foraging habitat is best in mixedwood stands (10-90% deciduous composition) so S5 is set at 1 in those conditions. Pure deciduous was considered to be half as good as the mixedwood stands and was set at 0.5. Pure conifer stands (deciduous = 0%) were set at 0.4 as they are assumed to produce less food (Figure 1e).

S6 Tree canopy closure is set so non-forested areas are unsuitable. Positive values only occur after 6% closure is reached. The value is optimum at 20% and remains optimal till 100% (Figure 1f).

S7 Stands with mean canopy tree heights ranging from 0-8 m are unsuitable foraging locations (S7 = 0). From 8-16 m the suitability increases to a value of 1. At all heights ≥ 16 m it is assumed that the stand structure has matured to the optimum condition for both prey abundance and diversity (Figure 1g).

NOGO-8

7.3 MODEL ASSUMPTIONS

1. Reproductive habitat (nesting and post-fledging habitat within range of adequate foraging habitat) is the most limiting component of year-round northern goshawk habitat. All other habitat needs are provided in the reproductive habitat.

2. For optimal reproductive habitat at least 4 potential nesting sites within a 1 km radius circle should be available, which is equivalent to 50 HU of nesting habitat.

3. Tree canopy closures of nesting location are usually higher than the closure in the surrounding forest. However the average forest condition relates best to the surrounding forest. Thus, mean stand canopy closures at which nesting becomes suitable is assumed to be less than the individual values reported in the literature.

4. Due to the cosmopolitan eating habits of the northern goshawk, a wide range of forest stand types will provide optimum foraging habitat conditions.

NOGO-9

a) Tree Canopy Height

0

0.2

0.4

0.6

0.8

1

0 4 8 12 16 20 24

(m)

S 1

b) Tree Canopy Closure

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

(% )

S 2

c) Deciduous in Tree Canopy

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

(% )

S 3

d) Dis tance to Human Dis turbance

00.2

0.40.6

0.81

0 50 100 (m)

S 4

e) Deciduous in Tree Canopy

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100

(% )

S 5

f) Tree Canopy Closure

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100 (% )

S 6

g) Tree Canopy Height

0

0.2

0.4

0.6

0.8

1

0 4 8 12 16 20 24

(m)

S 7

Figure 1. Graphical relationship between habitat variables and HSI components in the northern goshawk model.

NOGO-10

7.4 EQUATIONS

A. Nesting

The nesting equation considers the first 4 components to be equal and non-compensatory. Thus, a low value in any of the components cannot be compensated by a high value in another. Note that component S3 is unable to reduce the suitability to 0 since it is only a modifying component.

HSI-nesting = S1 x S2 x S3 x S4

B. Foraging

Like the nesting equation, the foraging HSI also considers the remaining three components to be equal and non-compensatory. The deciduous composition component (S5) is only a modifying component, but both tree canopy closure and tree canopy height (which predict S6 and S7) can drive the suitability to zero.

HSI-foraging = S5 x S6 x S7

To calculate the suitability of an area for northern goshawk nesting one must not only consider the suitability of the nest site and forage site but also the amounts of each present in an area. To accommodate the need for multiple nest sites a certain minimum amount of suitable habitat must be available within a 1 km area. More than 10 HU of nesting habitat must be available to be of any use and is best when there are more than 50 HU in the area. Likewise, the nesting habitat is unsuitable if there is not sufficient foraging habitat in the home range area for the post-fledging family. There must be at least 150 HU of foraging habitat within 1 km of the nest site and it is best to have more than 200 HU (Figure 2).

Nes ting HU within 1 k m of S tand

0

0.20.4

0.60.8

1

0 25 50 75 100

Habitat Units

S 8

Foraging HU within 1 k m of S tand

00.20.4

0.60.8

1

0 100 200 300 400

Habitat Units

S 9

Figure 2. HSI reproductive components predicted in relation to the sum of the HU around each potential

nesting habitat area.

8. SOURCES OF OTHER MODELS No other HSI models for the northern goshawk were found.

Model History

All of the HSI models for the Weldwood Forest Management Area have undergone several revisions, and they will be revised again as new information becomes available. Contact Rick Bonar for information about the most current version.

• Version 1 (1995) was written by Warren Schaffer based on data collected during Warren’s M.Sc. program at the University of Alberta, consultation with scientific literature and expert opinion.

• Version 2 (1996) was edited and reformatted by Wayne Bessie.

• Version 3 (1999) was revised by Karen Graham, Rick Bonar, Barb Beck, and Jim Beck to incorporate information from recent literature.

NOGO-11

9. LITERATURE CITED

Apfelbaum, S. I., and P. Seelbach. 1983. Nest tree, habitat selection and productivity of seven North American raptor species based on the Cornell University nest record program. Raptor Research 17:97-113.

Austin, K. K. 1993. Habitat use and home range size of northern goshawks in the Southern Cascades. Thesis, Oregon State University, Corvallis, Oregon.

Banfield, A. W. F. 1974. The mammals of Canada. University of Toronto Press, Toronto, Ontario.

Beckingham, J. D., I. G. W. Corns and J. H. Archibald. 1996. Field guide to ecosites of west-central Alberta. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre, Edmonton, Alberta, Special Report 9.

Beebe, F. L. 1974. Field studies of the falconiformes of British Columbia. British Columbia Provincial Museum, Occasional Paper Series No. 17.

Beier, P., and J. E. Drennan. 1997. Forest structure and prey abundance in foraging areas of northern goshawks. Ecological Applications 7:564-571.

Boal, C. W., and R. W. Mannan. 1994. Northern goshawk diets in ponderosa pine forests on the Kaibab Plateau. Studies in Avian Biology 16:97-102.

Bosakowski, T., D. G. Smith, and R. Speiser. 1992. Niche overlap of two sympatric-nesting hawks Accipiter spp. in the New Jersey-New York highlands. Ecography 15:358-372.

Bosakowski, T., and R. Speiser. 1994. Macrohabitat selection by nesting northern goshawks: implications for managing eastern forests. Studies in Avian Biology 16:46-49.

Bright-Smith, D. J., and R. W. Mannan. 1994. Habitat use by breeding male northern goshawks in northern Arizona. Studies in Avian Biology 16:58-65.

Brown, L., and D. Amadon. 1968. Eagles, hawks and falcons of the world, parts 1 and 2. McGraw-Hill Book Company, New York.

Bull, E. L., J. E. Hohmann. 1994. Breeding biology of northern goshawks in northeastern Oregon. Studies in Avian Biology 16:103-105.

Call, M. W. 1978. Nesting habitats and surveying techniques for common western raptors. US Department of the Interior, Bur. Land Management.

Crocker-Bedford, D. C. 1990. Goshawk reproduction and forest management. Wildlife Society Bulletin 18:262-269.

Crocker-Bedford, D. C., and B. Chaney. 1988. Characteristics of northern goshawk nesting stands. Pages 210-217 in R. L. Glinski, B. Giron Pendleton, M.B. Moss, M.N. LeFranc, B.A. Millsap, S.W. Hoffman, editors. Proceedings of the Southwest Raptor Management Symposium and Workshop. National Wildlife Federation, Science and Technology Series No. 12.

DeStephano, S., S. K. Daw, S. M. Desimone, and E. C. Meslow. 1994. Density and productivity of northern goshawks: implications for monitoring and management. Studies in Avian Biology 16:88-91.

Doyle, F. I., and J. N. M. Smith. 1994. Population responses of northern goshawks to the 10-year cycle in numbers of snowshoe hares. Studies in Avian Biology 16:122-129.

Eng, R. L., and G. W. Gullion. 1962. The predation of goshawks upon ruffed grouse on the Cloquet Forest Research Center, Minnesota. Wilson Bulletin 74:227-242.

Godfrey, W. E. 1986. The birds of Canada (Revised Edition). National Museum of Natural Sciences, National Museums of Canada, Ottawa, Ontario.

Grier, J. W., and R. W. Fyfe. 1988. Pages 173-182 in R. L. Glinski, B. Giron Pendleton, M. B. Moss, M. N. LeFranc, B. A. Millsap, S. W. Hoffman, editors. Proceedings of the Southwest Raptor Management Symposium and Workshop. National Wildlife Federation Science and Technical Series No. 12.

NOGO-12

Hall, P. A. 1984. Characterization of nesting habitat of goshawks (Accipiter gentilis) in northwestern California. Thesis, Humbolt State University, Arcata, California

Hargis, C. D., C. McCarthy, R. D. Perloff. 1994. Home range size and habitats of northern goshawks in eastern California. Studies in Avian Biology 16:66-74.

Hayward, G. D., and R. . Escano. 1989. Goshawk nest-site characteristics in western Montana and northern Idaho. The Condor 91:476-479.

Henderson, A. P. 1924. Nesting habits of the American goshawk. The Canadian Field Naturalist 38:8-9.

Janes, S. W. 1985. Habitat selection in raptorial birds. Pages 159-188 in M. L. Cody, editor. Habitat selection in birds. Academic Press, Toronto, Ontario.

Johnsgard, P. A. 1990. Hawks, eagles and falcons of North America. Smithsonian Institution, Washington, D.C.

Johnson, D. R. 1978. The study of raptor populations. University Press of Idaho, Moscow.

Jones, S. 1979. Habitat management series for unique or endangered species, Report No. 17, Technical Note. U.S. Department of the Interior - Bureau of Land Management.

Kaufman, K. 1996. Lives of North American birds. Houghton Mifflin Company, New York.

Keith, L. B., A. W. Todd, C. J. Bird, R. S. Adamcik, and D. H. Rusch. 1977. An analysis of predation during a fluctuation of snowshoe hares. Proceedings of the International Congress Game Biology 13:151-175.

Kennedy, P. L. 1990. Home ranges of northern goshawks in north central New Mexico. Abstract. in P. R. Klausmen, and N.S. Smith. Editors. Managing wildlife in the southwest. Arizona Chapter of the Wildlife Society.

Kennedy, P. L. 1988. Habitat characteristics of Cooper's hawks and northern goshawks nesting in New Mexico. Pages 218-227 in R. L. Glinski, B. Giron Pendleton, M. B. Moss, M. N. LeFranc, B. A. Millsap, S. W. Hoffman, editors. Proceedings of the southwest raptor management symposium and workshop. National Wildlife Federation Science and Technical Series No. 12.

Kennedy, P. L., J.M. Ward, G. H. Rinker, and J. A. Gessman. 1994. Post-fledgling areas in northern goshawk home ranges. Studies in Avian Biology 16:75-82.

Kirk, D. A. 1995. Forest management and the northern goshawk (Accipiter gentilis): with special reference to Ontario. Ontario Ministry of Natural Resources, Central Region Science and Technology Unit, North Bay, Technical Report No. 34 (draft), North Bay, Ontario.

Lanier, J. W., and C.F. Foss. 1989. Habitat management for raptors on large forested tracts and shorelines. Pages 203-208 in B. Giron Pendleton, editor. Proceedings of the northeast raptor management symposium and workshop. National Wildlife Federation Science and Technical Series No. 13.

Marti, C. D. 1987. Raptor food habits studies. Pages 67-80 in B. A. Giron Pendleton, B. A. Millsap, K. W. Cline, and D. M. Bird, editors. Raptor techniques manual. National Wildlife Federation, Washington, D.C.

McCarthy, C., W. D. Carrier, W. F. Laudenslayer. 1989. Coordinating timber management activities with raptor nesting habitat requirements. Pages 229-235 in Proceedings of the western raptor management symposium and workshop. National Wildlife Federation, Washington, D.C.

Mehl, M. S. 1992. Old-growth descriptions for the major forest types in the Rocky region. Pages 106-120 in M.R. Kaufmann, W. H. Moir, and R. L. Bassett, technical coordinators. Old-growth forests in the southwest and Rocky Mountain regions: proceedings of a workshop. General Technical Report RM-213, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.

Meng, H. 1959. Food habits of nesting Cooper’s hawks and goshawks in New York and Pennsylvania. The Wilson Bulletin 71(2):169-174.

Moir, W.H. 1992. Ecological concepts in old-growth forest definition. Pages 18-23 in M. R. Kaufmann, W. H. Moir, and R. L. Bassett, tech. coordinators. Old-growth forests in the southwest and Rocky Mountain

NOGO-13

regions: proceedings of a workshop. General Technical Report RM-213. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO. 207 pp.

Moore, K. R., and C.J. Henny. 1983. Nest site characteristics of three coexisting Accipiter hawks in northeastern Oregon. Raptor Research 17:65-76.

Mueller, H. C., D. D. Berger, and G. Allez. 1977. The periodic invasions of goshawks. Auk 94:652-663.

Palmer, R. S. 1988. Handbook of North American birds. vol. 4. diurnal raptors. Yale University Press, New Haven.

Perala, D.A. 1990. Populus tremuloides. Pages 555-569 in R. M. Burns, and B. H. Honkala, technical coordinators. Silvics of North America. Agriculture Handbook 654, United States Department of Agriculture, Forest Service, Washington, D.C.

Reynolds, R. T. 1989. Accipiters. Pages 92-101 in B. G. Pendleton, C. E. Ruibal, D. L. Krale, K, Steenhof, M. N. Kochert, and M. N. LeFranc, editors. Proceedings of western raptor management symposium and workshop. National Wildlife Federation Science Technical Series No. 12.

Reynolds, R. T. 1983. Management of western coniferous forest habitat for nesting Accipiter hawks. General Technical Report RM-102. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.

Reynolds, R. T., R. T. Graham, M. Hildegard Reiser, R. L. Bassett, P. L. Kennedy, D. A. Boyce, G. Goodwin, R. Smith, and E. L Fisher. 1992. Management recommendations for the northern goshawk in the southwestern United States. US Department of Agriculture, Forest Science, Rocky Mountain Forest and Range Experiment Station. General Technical Report RM-217. Ft. Collins, CO.

Reynolds, R. T., and S. M. Joy, and D. G. Leslie. 1994. Nest productivity, fidelity, and spacing of northern goshawks in Arizona. Studies in Avian Biology 16:106-113.

Reynolds, R. T., and E. C. Meslow. 1984. Partitioning of food and niche characteristics of coexisting accipiters during breeding. Auk 101:761-779.

Reynolds, R.T. , E.C. Meslow, and H.M. Wight. 1982 . Nesting habitat of coexisting accipiter in Oregon. Journal of Wildlife Management 46:124-138.

Reynolds, R. T., and H. M. Wight. 1978. Distribution, density, and productivity of accipiter hawks breeding in Oregon. Journal of Wildlife Management 46:124-138.

Richardson, C. T., and C. K. Miller. 1997. Recommendations for protecting raptors from human disturbance: a review. Wildlife Society Bulletin 25:634-638.

Schaffer, W. W. 1998. Northern goshawk (Accipiter gentilis) habitat characterization in central Alberta. Thesis, University of Alberta, Edmonton, Alberta.

Schnell, J. H. 1958. Nesting behavior and food habits of goshawks in the Sierra Nevada of California. The Condor. 60:377-403.

Shuster, W. C. 1980. Northern goshawk nest site requirements in the Colorado Rockies. Western Birds 11:89-96.

Semenchuk, G. P. 1992. The atlas of the breeding birds of Alberta. Federation of Alberta Naturalists, Edmonton, Alberta.

Siders, M. S., and P. L. Kennedy. 1994. Nesting habitat of accipiter hawks: is body size a consistent predictor of nest habitat characteristics? Studies in Avian Biology 16:92-96.

Snyder, N. F. R., and J. W. Wiley. 1976. Sexual size dimorphism in hawks and owls of North America. Ornithological Monographs No. 20.

Speiser, R., and T. Bosakowski. 1987. Nest site selection by northern goshawks in northern New Jersey and southeastern New York. The Condor 89:387-394.

Squires, J. R., and L. F. Ruggiero. 1996. Nest-site preference of northern goshawks in south-central Wyoming. Journal of Wildlife Management 60:170-177.

NOGO-14

NOGO-15

Storer, R. W. 1966. Sexual dimorphism and food habits in three North American Accipiters. The Auk 83:423-436.

Widen, P. 1989. Hunting habitats of goshawks (Accipiter gentilis) in boreal forests of central Sweden. Ibis 131:205-213.

Wildlife Management Division. 1996. The status of Alberta wildlife. Alberta Environmental Protection, Natural Resources Service, Wildlife Management Division.

Woodbridge, B., and P. J. Detrich. 1994. Territory occupancy and habitat patch size of northern goshawks in the southern Cascades of California. Studies in Avian Biology 16:83-87.

Zachel, C. R. 1985. Food habits, hunting activity, and post-fledging behavior of northern goshawks (Accipiter gentilis) in interior Alaska. Thesis, University of Alaska, Fairbanks, Alaska.