May to August 1994-2002, Northern Goshawk inventories were conducted on Vancouver Island, B.C. Broadcast surveys were conducted within previously known nest areas that appeared inactive during incubation as well as within forests where goshawk nests were unknown. Stand-watches and dawn vocalization surveys were also conducted to supplement broadcast survey efforts, and prey surveys occurred to track changes in the relative abundance of goshawk prey. Occupancy at previously known nest areas, nesting success, nest productivity, and small-scale nest site habitat characteristics were recorded, and morphometric data and blood were gathered for genetic analyses. Goshawks built nests primarily in large Douglas-fir and western hemlock trees in stands with moderate to high canopy closure on moderate slopes below 900 m. Goshawks were present in 55% of 44 known nest areas during 163 occupancy assessments. Occupancy rates were significantly lower in fragmented forests. Nest productivity varied annually within nest areas, but varied little among nest areas over time. Prey detections varied annually with no apparent pattern. Relatively low detection rates and few nests discovered per unit of survey effort suggest goshawk breeding population densities on Vancouver Island are low. Although fragmented nest areas had significantly lower occupancy than more contiguous nest areas, more data is required to understand the amount of fragmentation goshawks can withstand in landscapes (i.e. foraging areas) around nest areas. Breeding densities are lower than in the SE USA, but higher than in SE Alaska, likely reflecting a combination of prey and breeding habitat availability. In Vancouver Island study areas, most goshawks were non-migratory, and merely expanded their breeding home range during the winter months. Genetic evidence for subspecific status determination is ongoing.
McClaren, E.L.. 2005. Northern Goshawk (Accipiter gentilis laingi) Population Inventory Summary for Vancouver Island, British Columbia 1994-2002. Ministry of Environment. Wildlife Bulletin. B-117