Abstract (pg.xiii)
I investigated the nesting ecology and habitat of a previously unstudied population of the northern Goshawk on the Targhee National Forest in eastern Idaho/southwestern Wyoming from 1989 to 1995. Twenty-seven current and 4 historical territories in Douglas fir and lodgepole pine habitat were monitored. The study was designed to gain an understanding of local habitat requirements during the breeding season, prey use, and patterns of occupancy and productivity. I also wanted to determine how timber harvesting was changing habitat within estimated home range areas, and whether habitat changes resulting from harvesting were affecting productivity and occupancy. Habitat analysis areas included: the nest tree, nest plot (.13 ha), nest area (NA 81 ha), post-fledging family area (PFA 162 ha), and foraging area (FA 2428 ha).
At 10 territories monitored pre- and post-harvest, timber harvesting significantly reduced the amount of mature forest within the home range area with the greatest reduction within the NA (33%). Average occupancy rate decreased in the post-harvest period from 79% to 47% at these territories but this was not significant. Occupancy at 15 post-harvest territories was positively related to the amount of mature forest cover retained with the NA. Large decreases in mature forest cover at three historical territories in salvage logging areas indicate the need modifications of current silvicultural practices to maintain goshawk nesting habitat over time in timber management areas.
Conclusions (pg.82)
Similar to other studies, goshawks in the TNF tended to nest in home ranges that had higher greater basal area, taller trees, greater under canopy space, and higher density trees in the 38-45.5 cm dbh size class. Nesting territories contained alternate nests (1-7), 87% of alternate nests used were located >100 from a previously used nest. Alternate nests provided important nesting sites for Great Gray Owls on the TNF. Nesting areas with a home range primarily in Douglas fir/mixed conifer habitat had a higher mean productivity compared to sites in lodgepole pine habitat. The amount of sage/shrub habitat within the post family fledging area (PFA) and overall foraging area proved to be important for providing consistent foraging opportunities.
Management Implications (pg. 83)
Goshawk habitat management guidelines should include: (1) protection of core areas and high quality foraging habitat in traditional nesting territories, (2) extended rotation times for treatment of individual stands throughout the TNF, (3) conservation of intact patches of productive lower elevation mature and old growth forests and, (4) managing younger stands in disturbed areas to create future goshawk habitat. Managing at the landscape level for goshawks could provide habitat for other forest dependent species such as the Great Gray Owl.
In the TNF, average forest canopy cover in undisturbed areas was greater than in other studies in the southwest (TNF, NA=83%, PFA=77%, FA=68%). While the 60% canopy cover may be adequate in some parts of the forest it may not be enough in other parts of the TNF. If extensive timber harvesting continues it is unknown whether goshawks will continue to use disturbed areas over time. Timber practices on the TNF are quite different (clearcuts) than on southwestern forests where selection, and uneven aged harvesting methods are used. Recommendations for the southwest and the amount of mature forests needed for goshawks may not be the same for the TNF and other forests in the northwest.