The Northern goshawk (Accipiter gentilis) is the largest accipiter species found in North America. Other accipiters found in the United States include the Coopers hawk and sharp-shinned hawk. North American breeding distribution for the goshawk includes most of Alaska and Canada, most Northern states and the Intermountain West. Suitable forging habitat includes boreal and temperate forests. Nesting tends to occur in mature deciduous forests in the East and mature coniferous forests in the West. The goshawk’s short, broad wings and long tail allow the bird to be a skillful hunter in the forest. Goshawks count birds and rodents among their varied prey. In the late 1990’s the U.S. Fish and Wildlife Service (USFWS) was petitioned to list the Northern goshawk for protection under the Threatened and Endangered Species Act in the Western United States. However, the USFWS determined not enough data existed on goshawk populations to justify listing the species for protection. The U.S. Forest Service (USFS) then designated the goshawk as a sensitive species in six of eight Forest Service regions. This designation was assigned because of the goshawk’s dependence on mature forests for nesting and because potential resource use of these forests may affect goshawk populations. Under this designation, USFS officials are required manage areas in a way that “must not result in loss of species viability or create significant trends toward Federal listing”. Therefore, monitoring must be conducted to evaluate trends in goshawk populations throughout the United States. The Northern Goshawk Inventory and Monitoring Technical Guide was published in 2006 by the USFS as a “consistent and credible” method to implement large-scale monitoring. Rocky Mountain Bird Observatory (RMBO) collaborated with Region 2 of the USFS in 2006 to implement large-scale monitoring of Northern goshawks in most of the forests of South Dakota, Wyoming and Colorado. Using geospatial software, a grid was laid down on the designated forests consisting of 688 hectare units containing suitable habitat for goshawks. The actual sampling area within the 688 hectare grid unit consists of a 600 hectare area. Broadcast Acoustical Surveys are performed at a maximum of 120 call stations located along transects within the sampling unit. Broadcast Acoustical Surveys require individuals conducting the survey to play goshawk calls at the call stations to elicit responses from goshawks in the area. Once the surveyor identifies a goshawk by sight and/or sound, the unit is considered to have a “presence” and the survey for that unit is completed at that time. If the surveyor does not get a response from a goshawk, he or she will continue playing calls in the sampling unit until identification occurs or all call stations have been visited. Most sampling units are visited twice during the nesting season to minimize false-negative detection. In 2006, 51 sampling units were surveyed in the Rocky Mountain region and approximately 33% of those sites were occupied by goshawks.
Furthermore, RMBO, in cooperation with the USFS, wants to validate sampling methodology outlined by the Northern Goshawk Inventory and Monitoring Technical Guide. This validation process began in 2008 when RMBO conducted surveys on the Kaibab National Forest. Richard Reynolds, a Research Wildlife Biologist with the U.S. Forest Service, has been studying Northern goshawks in this forest for over a decade and has a solid understanding of the goshawk’s occupancy rates. The data collected from the 2008 sampling design is still being evaluated and will be compared with the long-term occupancy rates determined by Reynolds.
In 2009, RMBO and the USFS hope to undertake surveys in approximately 120 sampling units in Region 2 as well as expand the surveys into Region 3 in Arizona. This increase of sampling units and the expansion into new areas should increase the accuracy and scope of the data collected. Also, once these surveys are conducted on a year to year basis, trends in population can be determined. All of this information will help forest and wildlife managers make better judgments when deciding on actions that may affect Northern goshawk populations. For more information contact: Jenny Berven Northern Goshawk Project Coordinator Jenny.Berven@rmbo.org or (970) 482-1707 x26