Background / Reason for Study
Northern goshawks (Accipiter gentilis) typically select large stands of mature forest for breeding season home ranges. Because of this, state and federal agencies designate it as “Sensitive” and “of Special Concern.” Preserving specific forest habitats is critical to goshawk persistence, yet goshawk foraging habitat selection is poorly understood in North America. Most home range studies indicate that goshawks typically use large areas (2,400 ha) dominated by dense forest cover. However, there is evidence to suggest that home ranges may become much smaller (i.e., 1,200 ha) in naturally-fragmented shrub-steppe habitat. This little-documented, “atypical habitat” in southern Idaho likely supports the highest goshawk nesting density in the western US, which presents intriguing research questions.
Description of Work
This study will focus on goshawk foraging habitat selection on the Sawtooth National Forest (SNF) in south central Idaho. The observation that this dense goshawk population is supported by atypical habitat provided the impetus for this investigation. Research questions include: What kinds of habitats, and in what proportions and/or amounts, are required to support a goshawk family during the critical nestling phase? And what factors (home range size, prey species used, productivity), if any, are associated with habitat type and/or features? Males are the primary hunters and food providers for the female and young until the young fledge, and therefore are the appropriate cohort for studying foraging habitat.
My field assistants and I tracked three male northern goshawks throughout the nestling period, when hunting activity peaks, in 2001. I will attempt to radio-track another nine in 2002. (Only three males were tracked in 2001 due to unusually low nest occupancy rates.) I calculated home range sizes using RANGESV, and will correlate telemetry points with habitat features using Geographic Information System (GIS) data provided by the SNF. For results from the 2001 season, see abstract below.
This study add to our knowledge goshawk habitat use in the western U.S. Data generated will result in goshawk management guidelines for this habitat type.
The “activity switches” in the transmitters that were supposed to indicate if the bird was perching or flying didn’t appear to be working all of the time. Often, we would see the bird flying and we’d be hearing a perching signal, and vice versa. If anyone has any insight to this, I’d appreciate it.
It was a very low-occupancy year for nesting. We tracked birds from the only three successful nests we found out of 23 known nest sites. In a typical nesting year, we would have had approximately 15 successful nests. My only advice for this is have a backup plan for a situation where the birds don’t nest.
We also had an entire nest full of young taken by falconers. Goshawks are popular falconry birds, and their harvest in your study area may be something to consider. I’d advise contacting your state’s falconry association to notify them of your study and perhaps request that harvest be discouraged in your area before beginning field work.
Major funding for this project was provided by the Sawtooth National Forest. The Idaho Department of Fish and Game made major financial and in-kind contributions as well. Idaho Bird Observatory personnel have made significant contributions through fieldwork on this population over the last three years, and through assisting me with trapping goshawks and finding new nests. Others I would like to thank include: the USGS Snake River Field Station for equipment loans, Ray and Sonnie Strolberg for their housing donation, Marty and Sherri Jacobs of Magic Mountain Ski Area for logistical support, and technicians Haley Breniser and Marianne Farris for their long hours of goshawk tracking.
Abstract for 2001 RRF Meeting:
Northern Goshawk (Accipiter gentilis) Home Ranges in a Naturally-Fragmented Forest Landscape in Southern Idaho.
*KRISTIN W. HASSELBLAD and MARC J. BECHARD, Raptor Research Center, Department of Biology, Boise State University, 1910 University Drive, Boise, ID 83725 USA.
The South Hills of Idaho’s Sawtooth National Forest supports a dense population of breeding Goshawks. The habitat consists of naturally-fragmented lodgepole pine (Pinus contorta) and aspen (Populus tremuloides) stands, interspersed with shrub-steppe communities dominated by sage brush (Artemesia tridentata). Three breeding male goshawks were trapped and radio-tagged in 2001. They were followed throughout the nesting season (from the time young were approximately 10 d old to 22 d after fledging (9 June to 14 August). A total of 185 points, collected at least one hour apart, were used in this analysis. 175 locations were obtained through triangulation, while 10 were visual observations. Mean number of points used for each home range analysis was 62 (range = 58-66). Home range (100% MCP) sizes for the three males were 390 ha, 588 ha, and 2068 (mean = 1015 ha). Although this data is preliminary, it suggests that breeding male goshawk home ranges in the South Hills may be much smaller than those typically reported (i.e., 2,400 ha).
Hasselblad, K. and M. Bechard. 2007. Male Northern Goshawk home ranges in the Great Basin of south-central Idaho. Journal of Raptor Research 41:150-155.