Kristin Wood Hasselblad

Northern Goshawk Home Ranges and Habitat Selection in South Central Idaho

To measure Northern Goshawk (Accipiter gentilis) home range sizes and habitat selection in naturally-fragmented forests of south central Idaho, I radio-tracked six adult males throughout their breeding seasons in 2001 and 2002.  Males were tracked from the time young were 5-10 d old until 20 d post-fledging.  I collected 485 temporally-independent locations, with a mean of 54 ± 3.3 (±SE) such locations per bird.  Average linear error associated with triangulated locations was 130 ± 15 m. Median minimum convex polygon home range size was 588 ha for males that successfully fledged young, and 542 ha for unsuccessful males.  Median 85% cluster core area size was 98 ha for successful males, and 70 ha for unsuccessful males.  Home ranges of neighboring males overlapped by an average of 19%.  These home ranges were smaller than any previously reported for goshawks in North America and may have been due to a super abundance of hunting areas, such as edge areas where forest and shrub steppe habitats interfaced and goshawks perched to hunt open-country prey, especially ground squirrels. 

I assessed goshawk habitat selection at two scales [perching/hunting sites within the home range (Johnson’s 3^rd order), and home range placement within the larger study area (Johnson’s 2^nd order)].  Habitat variables measured included:  distance from used (obtained through radio telemetry) and available (randomly selected within home ranges) locations to the nearest seedling (< 2.5 cm dbh) stand, sapling/pole (2.6-12.9 cm dbh) stand, "small tree" (13-34 cm dbh) stand, road/trail, and camp area.  “Small tree” habitat constituted the largest trees in the study area.  I used logistic regression to identify those features that may be important in predicting individual goshawk use of a perching site.  Five out of six males selected perching sites closer to "small tree" habitat and camp areas than expected.  Two males selected perching locations closer to roads/trails than expected, and two males selected higher or lower elevations than expected.  I examined habitat selection at the scale of home range placement within the study area using home-range sized sampling ellipses placed around 23 known historical nests, and 23 randomly selected locations within the study area.  At this scale, goshawks selected for less sapling/pole habitat, and greater habitat diversity as measured by Shannon's diversity index, similar to results from other studies.