Multi-Scale Habitat Influences on Northern Goshawk Occupancy and Reproduction on Washington's Olympic Peninsula

• Main Author: Finn, Sean Paul
• Format: Text
• Language: unknown
• Published: ScholarWorks 2000
• Subjects: Ornithology; Accipiter gentilis; Northern Goshawk
• Online Access: https://scholarworks.boisestate.edu/td/440; https://boisestate.on.worldcat.org/v2/oclc/46468973

Large, mobile organisms can move swiftly through their environment and probably select resources, from those available, at a relatively coarse grain. The Northern Goshawk (Accipiter gentilis), a large mobile raptor, is known as a forest generalist throughout its holarctic range, yet individual populations seem to prefer specific habitats in a given region. To determine goshawk habitat relationships and the spatial scales at which they operate I surveyed all known historical nest sites on the Olympic Peninsula, Washington (N = 30) and compared goshawk occupancy and reproductive success at these sites to existing habitat conditions at a range of spatial scales that might be important to a breeding pair. A historical nest site was defined as a location that contained a large stick nest and was occupied by an adult goshawk at least one year between 1975-1995. I estimated goshawk occupancy one year at each historical nest site, from 1996-1998, using standardized aural broadcast surveys within a 170-314 ha circular plot surrounding the most recently built nest. I assessed among-year variation in occupancy by surveying a subset of 10 historical nest sites each of the three years. Occupancy remained consistent among years at these 10 sites (Fisher's Exact Tests, P ≤ 0.07) so I characterized all 30 historical sites as 'occupied' or 'unoccupied' based on one- year surveys. Reproductive success at occupied historical sites was estimated during two visits to the site during the post-fledging period. The maximum number of fledged young observed was used to index the relative success of each breeding pair. I characterized occupancy and reproductive success at historical sites in terms of existing habitat condition by comparing them to 175 individual habitat attributes at six spatial scales - the nest tree (0.003 ha), nest vicinity (0.04 ha), nest stand (9 - 146 ha), nest area (38.5 ha), Post-fledging Family Area (PFA; 176.7 ha), and home range (1885.5 ha) - surrounding the historical nest sites. I measured attributes at the ...