Spelling suggestions: "subject:"goshawk -- abitat -- oregon"" "subject:"goshawk -- abitat -- pregon""
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Northern goshawk nest site selection and habitat associations at the post-fledging family area scale in OregonDaw, Sonya Kathleen 07 May 1996 (has links)
Graduation date: 1997
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Occupancy rates and habitat relationships of northern goshawks in historic nesting areas in OregonDesimone, Steven M. 20 June 1997 (has links)
The ability of northern goshawks (Accipiter gentilis) to persist in intensively
managed and selectively harvested forest habitats is largely unknown. To address the
concern that populations of northern goshawks in eastern Oregon may be declining in
response to habitat alteration, I studied occupancy rates and habitat relationships of
nesting goshawks on the Fremont National Forest and adjacent private lands during
1992-1994. My objectives were to determine if historic territories (i.e., those occupied ��� 1
season during 1973-1991) were still occupied, document current site conditions and
quantify changes in forest cover on those territories between 1973-1994, and compare
present conditions of forest vegetation between nest sites that were currently occupied
and those where I did not detect the presence of territorial goshawks (no-response
sites). In 1994, I surveyed a forest-wide random sample of 51 historic nest sites,
stratified by forest cover type. Occupancy of historic sites by goshawks was 29% (15 of
51), compared to 79% (30 of 38) mean annual occupancy rate of current territories
(found initially during 1992-1994). Across all strata, 86% of current nest sites (n=38)
were in Mid-aged or Late structural stage forest (trees >23 cm DBH) with >50% canopy
closure. Among the historic territories used for analysis (n=46), those found occupied
(n=15) in 1994 had significantly more Mid-aged Closed forest (average stand DBH 23-53 cm, <15 trees per ha >53 cm DBH; >50% canopy closure) and Late Closed forest (15 trees per ha >53 cm DBH; >50% canopy closure) than no-response sites (n=31). This relationship was significant (P<0.05) for circular scales of 12, 24, 52, 120, and 170 ha surrounding goshawk territory centers. Within the 52 ha scale around historic nest sites surveyed in 1994, occupied sites had 49% (SE=6.6) total Late Closed and Mid-aged Closed forest, while sites with no response had 19% (SE=3.0) total Late and Mid-aged Closed forest. Historic sites had 51% (SE=3.8) total Late and Mid-aged Closed forest when last known occupied before 1992. Among historic territories, mean percent area of habitat in Late Closed forest at the 12 ha nest stand scale was 4 times greater in occupied (27%) than in no-response sites (6%) (P<0.05). A logistic regression model for occupied sites confirmed the importance of Late Closed and Mid-aged Closed forests as indicators of quality habitat within the 52 ha scale on historic sites where goshawks were still present in 1994. Goshawk pairs were more likely to persist in historic territories having a high percentage of mature and older forest (about 50%) in closed-canopied conditions within the 52 ha scale, suggesting that little or no habitat
alteration within aggregate nest stands is important to ensure the persistence of nesting
pairs. I recommend preserving multiple nest stands within the 52 ha scale and
discourage further cutting of large, late and old structure trees (>53 cm DBH) within the
PFA to preserve stand integrity, maintain closed canopies, maintain connectivity to
alternate nest stands, and optimize conditions for breeding goshawk pairs to persist. / Graduation date: 1998
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