Habitat use and home range size of breeding northern goshawks in the southern Cascades Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5h73q123g

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  • I investigated habitat use and home range size of northern goshawks in the southern Cascades, in the Shasta- Trinity and Klamath National Forests of northern California. My objectives were to 1) estimate the average home range and 2) describe the use of habitats within home ranges by breeding goshawks. Ten goshawks (5 males, 5 females) were trapped, radio-transmitters attached, and tracked for approximately 50 days during the breeding season in 1988 and 1989. A mean of 33 data points per bird (range = 27-43) produced home range estimates (100% minimum convex polygon method) of 2,425 ha (range = 1083-3902 ha) for 5 males and 3,774 ha (range = 2007-6908 ha) for 5 females. Vegetation plots were sampled at 20 locations determined by radio-tracking (used) and 20 locations randomly identified (available) in each of 9 goshawk home ranges. Two variables were sampled within 30-m radius habitat plots, average dbh and canopy closure. These variables were combined to classify the plot into 1 of 5 classes. Goshawks used habitats within their home ranges non-randomly. Analyses of individual goshawk habitat selection were not conclusive, but trends in individual habitat selection was used to examine pooled analysis results. Goshawks avoided open habitats (meadows, seedling and sapling stands) and individual trends supported pooled analysis results. Goshawks did not avoid or select pole habitat stands, and individual trends supported these results. Goshawks avoided open-canopied, small sawtimber and mature stands (26-52+ cm dbh, canopy closure < 40%), but trends in individual goshawk selection were inconsistent. Stands of closed-canopied, small sawtimber (26-51 cm dbh, canopy closure [greater than or equal to] 40%), the most abundant habitat type within goshawk home ranges was not selected or avoided by goshawks, and individual trends agree with pooled results. Goshawks selected closed-canopied stands of mature and old-growth habitat ([greater than or equal to] 52 cm dbh, canopy closure [greater than or equal to] 40%), and trends in individual goshawk selection generally agreed with pooled results. Management recommendations are not meant to be extrapolated beyond the limitations of my study, but in the absence of other information this data can be used in developing interim recommendations and can help focus future research efforts. The area considered for management of habitat for breeding goshawks should include a minimum of 4,765 contiguous hectares (11,774 acres), within which habitats should be managed for goshawk foraging, resting, nesting, and raising young. Habitats managed for goshawks should include a minimum of 20% of each area in closed-canopied mature and old-growth forest ([greater than or equal to] 52 cm or [greater than or equal to] 21" dbh, canopy closure [greater than or equal to] 40%), and a minimum of 40% in closed-canopied small sawtimber forest (26-51 cm, or 11-21" dbh, [greater than or equal to] 40% canopy closure). No more than 10% of the management area should be maintained in the seedling/sapling/grass-forb habitats and unforested condition.
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