Boal et al. 2001 summary

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Boal, C.W., D.E.Anderson, and P.L. Kennedy. 2001. Home range and habitat use of Northern goshawks (Accipiter gentilis) in Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. Unpaged.


The northern goshawk (Accipiter gentilis atricapillus) is a large, forest-dwelling raptor generally associated with mature deciduous, coniferous, or mixed forests (Siders and Kennedy 1996, Bright-Smith and Mannan 1994, Beier and Drennan 1997, Squires and Reynolds 1997). In the western Great Lakes Region (WGLR), the species is currently listed as a migratory nongame bird of management concern by the U.S. Fish and Wildlife Service (Region 3), and as a sensitive species by the U.S. Forest Service (Region 9). Although region-specific information on habitat use and productivity is essential for the development of sound management guidelines, active management of the species in the WGLR has been hampered by a lack of information specific to the region (Estabrook 1999, Kennedy and Andersen 1999). We assessed productivity of breeding goshawks in Minnesota, and used radio telemetry to estimate breeding season home range sizes and characterize foraging habitat of 19 male goshawks. Project cooperators located 15 occupied breeding areas in 1998, seven additional areas in 1999, and nine additional areas in 2000, for a total of 31 breeding areas occupied at least one year during the three-year period of the study. Mean fledging success was 1.14 +/- 0.17 fledglings per all nesting attempts (n = 42) and 1.85 +/- 0.14 per successful nesting attempt (n = 26). We radio-tagged 33 (18 male, 15 female) of 36 goshawks that were captured. The mean range estimate for male goshawks was 2,676 ha using the minimum convex polygon estimator and 3,953 ha using the 95% fixed kernel contour estimator. Male goshawks demonstrated a clear preference to forage in old (>50 yrs) early successional upland hardwood (e.g., aspen, birch) stands, mature (> 50 yrs) late successional upland conifers (e.g., red pine, white pine), and mature (> 25 yrs) early successional upland conifer (e.g., balsam fir, jack pine). Young (< 25 yrs) early successional upland hardwood and young (< 50 yrs) late successional lowland conifer (e.g., black spruce, tamarack) stands were clearly avoided. Foraging stands, regardless of stand type, were consistent in having high stem densities (570 - 1030 stems/ha) of tall, large canopy trees, with horizontal open spaces of 1.1 to 3.5 m between the bottom of the overstory and top of the understory trees, and up to 1 m between the bottom of the understory canopy and top of the shrub layer. These relatively unobstructed spaces between vegetation layers may serve as important flight paths through forest stands, and the heights in which they occurred were consistent among stand types. Mean canopy closure was high among all stand types (53-70%). Goshawks foraged in stands that, regardless of tree species, were remarkably similar in terms of diameter and heights of the canopy trees, canopy closure, and high stem density.

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