II

Species Accounts

Andy Birch

PDF of account from: Shuford, W. D., and Gardali, T., editors. 2008. Bird Species of Special Concern: A ranked assessment of species, subspecies, and distinct populations of birds of immediate conservation concern in California. Studies of Western Birds 1. Western Field Ornithologists, Camarillo, California, and California Department of Fish and Game, Sacramento. Studies of Western Birds No. 1

NORTHERN GOSHAWK (Accipiter gentilis) John J. Keane

Criteria Scores Population Trend 10 Range Trend 0 Population Size 7.5 Range Size 5 Endemism 0 Population Concentration 0 Threats 10

Year-round Range * * Historic Extralimital Breeding County Boundaries Water Bodies

Kilometers 100 50 0 100

Year-round range of the Northern Goshawk in California; numbers have declined at least moderately. Small num- bers of migrants or dispersing birds occur outside known breeding areas in the nonbreeding season.

156 Studies of Western Birds 1:156–162, 2008 Species Accounts California Bird Species of Special Concern

Special Concern Priority Historic Range and Abundance Currently considered a Bird Species of Special in California Concern (year round), priority 3. Included on the Grinnell and Miller (1944) described the species as list since its inception (Remsen 1978, 3rd priority; “not common” in its breeding range in the higher CDFG 1992). altitudes in the northern third of the state—south in the Coast Ranges to the vicinity of Laytonville Breeding Bird Survey Statistics and Mount Sanhedrin, Mendocino County, and for California in the Cascades and Warner Mountains—and further south in the Sierra Nevada to Kings Data inadequate for trend assessment (Sauer et Canyon National Park and Whitaker’s Forest, al. 2005). Tulare County. Information available to Grinnell and Miller was incomplete. In Ventura County, General Range and Abundance egg sets were collected from Mount Pinos in 1904 Holarctic distribution (Brown and Amadon 1968, (Kiff and Paulson 1997) and at an unspecified site Squires and Reynolds 1997). In North America, in 1919 (Delaware Mus. Nat. Hist. egg set). Also, breeds from boreal Alaska and Canada south in two egg sets were collected from the Cuyamaca the East as far as Pennsylvania and New York and Mountains, San Diego County, in 1937, and two in the West to the mountains of southern Arizona young birds were seen at one locality there in 1938 and New Mexico; disjunct populations occur in (Kiff and Paulson 1997, Delaware Mus. Nat. Hist. the mountains of western Mexico as far south as egg set). In winter, individuals were recorded from Jalisco and southern Guerrero (Howell and Webb lower elevations and the southern part of California 1995, Squires and Reynolds 1997). During winter, from near the coast to the lower Colorado River some birds are resident, whereas others are faculta- valley (Grinnell and Miller 1944). tive migrants exhibiting short-distance elevational or latitudinal movements. During irruption years, Recent Range and Abundance northern populations can exhibit long-distance in California migrations in response to large cyclic fluctuations A synthesis of historical and current breeding in prey populations (Squires and Reynolds 1997, and distributional records from federal and state Doyle and Smith 2001). agencies, private land management companies, The AOU (1957) recognized two subspe- museums, and published literature indicates that A. g. atricapillus cies: breeds throughout most Northern Goshawks are still well distributed across A. g. of the North American range except where their core breeding range in most of the northern laingi occurs. The latter was originally described Coast Ranges, the Klamath and Siskiyou moun- from the Queen Charlotte Islands and Vancouver tains, across the Cascades, Modoc Plateau, and Island but is now considered to extend north Warner Mountains, and south through the Sierra through insular and insular and Nevada (see map; J. Keane and B. Woodbridge coastal mainland Alaska to Icy Strait and Lynn unpubl. data). The compilation of records and Canal (Squires and Reynolds 1997). Recognition additional fieldwork have extended the known A. g. apache, of a third subspecies, resident from range (likely mostly occupied prior to 1944) southern Arizona through Mexico, is currently south to southern Mendocino County in the debated (Squires and Reynolds 1997). Coast Ranges, south past the Sierra Nevada to the Tehachapi Mountains, east to the Glass Mountain Seasonal Status in California region and White-Inyo ranges, and sparsely south Year-round resident throughout all or most of the to the Mount Pinos–Frazier Mountain area and California range, though in winter some individu- the San Gabriel, San Bernardino, San Jacinto, als remain on or close to breeding territories while and Cuyamaca mountains of southern California others migrate short distances to winter elsewhere (Garrett and Dunn 1981, Bloom et al. 1986, (Hargis et al. 1994, Keane 1999, D. J. Richter and Lentz 1993, Kiff and Paulson 1997, J. Keane R. Callas unpubl. data). Migrants from northern and B. Woodbridge unpubl. data). Breeding in populations likely occur in California during the Cuyamacas is best considered extralimital, some winters; irruptive movements into the state as there are no other breeding season records for are rare, but considerable numbers occurred across San Diego County, even of just adults, despite the southern California in the winter of 1916–17, an extensive fieldwork in 1997–2001 for the bird atlas invasion year (Grinnell and Miller 1944). (Unitt 2004). Breeding within the California range

Northern Goshawk 157 Studies of Western Birds No. 1 extends from about 1000 to 10,800 ft (305–3290 Westside Ponderosa Pine zone. Likewise, exten- m) in elevation. sive logging on the entire lower west slope of the Population trends of Northern Goshawks Sierra Nevada has eliminated 95% to 99% of the in California are poorly known. Distributional original old-growth Pacific Ponderosa Pine forests changes and loss of breeding territories from (Franklin and Fites-Kaufmann 1996). Goshawks timber harvest and wildfire across their range are known to nest down to about 2500 ft (750 m) suggests that population size has been reduced. on the west slope, so it is likely that reductions in Bloom et al. (1986) estimated a statewide popula- mature and old-growth pine has resulted in reduc- tion of approximately 1300 breeding territories. tions in goshawk numbers in these forests. Recent synthesis of existing breeding territory Southern Sierra Nevada. There have been only records documented approximately 1000 known about 25–30 recent nest records for the southern territories statewide between 1970 and 2001 Sierra Nevada south of (J. Keane and B. Woodbridge unpubl. data). (Sierra and Sequoia national forests, Sequoia–Kings That the majority of nest territory records were Canyon National Parks). It is uncertain whether reported from the previous 12 years reflects an this represents the limited survey effort expended increased conservation focus and development of in these areas, low breeding densities/suboptimal specialized survey procedures and efforts targeting habitat conditions near the southern edge of gos- Northern Goshawks. Christmas Bird Count data distribution in the southern Sierra Nevada, for California suggest a stable population between or potential reductions in densities or distribution 1959 and 1988, although estimates are of ques- at the edge of the species’ range. tionable reliability because of small sample sizes Southern California mountains. The historic and low abundance (Sauer et al. 1996). and current distribution of Northern Goshawks Concern exists for potential range contraction, in these mountains is uncertain because of limited reductions in breeding densities, and generally information. The few nest records—only seven low breeding densities in five areas of California confirmed and one suspected—suggest that gos- as outlined below. likely bred and continue to breed across Coastal Redwood zone. Concern exists for this region, although it is unknown how com- potential extirpations in the Redwood (Sequoia monly or regularly. In addition to the historical sempervirens) zone along the north coast, where nest records described above for Ventura and San there are very few current breeding records. In Diego counties, there are records of active nests 2001–2002, Weber (2006) conducted surveys at on Mt. Abel (1989–1990), Mount Pinos (1989), eight locations with prior nesting evidence and at and the Tecuya Range (1991) in northern Ventura many other sites with potential nesting habitat of County and reports of an active nest at one site mature or old-growth forest on public and private and an aggressive pair of adults during the breed- lands in the coastal Redwood region from Del ing period (1990–1991) at another site in the Norte to Sonoma counties. No nesting was docu- San Jacinto Mountains, Riverside County (Kiff mented within the Redwood zone proper, though and Paulson 1997, J. Keane and B. Woodbridge an active nest was found about 33 km inland at unpubl. data). Of the approximately 25 breeding- Angelo Coast Range Reserve, Mendocino County period sight records of adult goshawks from the (nesting known since 1977, B. Woodbridge pers. mountains of southern California over the past comm.), at the transition from Redwood to 50 years reported in Audubon Field Notes and its more xeric Douglas-fir (Pseudotsuga menziesii) and successors, about half were from the San Jacinto mixed-oak habitat (Weber 2006). Current records Mountains. Biologists conducting extensive sur- indicate that Northern Goshawks do not breed veys for California Spotted (Strix occidentalis in pure stands of Redwood, but that they do nest occidentalis) in the San Bernardino, San Gabriel, within stands of -hardwood and mixed and San Jacinto mountains from 1987 to 2003 Redwood-conifer-hardwood within and imme- did not record Northern Goshawks, with the diately adjacent to the broader coastal Redwood exception of one nesting pair in the San Jacintos vegetation zone. in one year (W. La Haye pers. comm.), mentioned Eastside pine zone. Northern Goshawks no above. longer occur in extensive areas of eastside pine forest, mainly Pacific Ponderosa (Pinus ponderosa) Ecological Requirements and Jeffrey (P. jeffreyi) pines, of northeastern California, where extensive railroad logging elimi- Key ecological requirements for Northern nated habitat (B. Woodbridge pers. comm.). Goshawks are suitable nesting and foraging habi-

158 Species Accounts California Bird Species of Special Concern tat, including adequate prey. Northern Goshawks Northern Goshawk populations exhibit high nest in mature and old-growth forest stands over annual variation in reproduction, with 30%– much of their California range. Suitable stands 90% of pairs breeding in any year. Variation in occur in a broad range of conifer and conifer- reproduction is associated with annual varia- hardwood types, including Pacific Ponderosa, tion in weather and prey abundance (Keane Jeffrey, and Lodgepole (P. contorta) pine, mixed 1999, Keane et al. 2006). Although Northern conifer, White (Abies concolor) and California Red Goshawks will prey on a large number of spe- (A. magnifica) fir, Douglas-fir, mixed Redwood– cies, several important species and species groups Douglas-fir–hardwood, and (rarely) pinyon-juni- dominate the majority of prey items and bio- per (P. monopylla, Juniperus spp.), as well as mass in California (Keane 1999, McCoy 1999, in mature Quaking Aspen (Populus tremuloides) Maurer 2000, Keane et al. 2006). These are stands within aspen–shrub steppe vegetation east the Douglas (Tamiasciurus douglasii), of the Cascade-Sierra axis. Nest stands have con- Golden-mantled Ground Squirrel (Spermophilus sistently larger trees, greater canopy cover, and rel- lateralis), Belding Ground Squirrel (S. beldingi), atively more open understories than stands lacking Western Gray Squirrel ( griseus), hares and nests (Saunders 1982, Hall 1984, Hargis et al. rabbits (Lepus spp., Sylvilagus spp.), chipmunks 1994, Keane 1999, Maurer 2000). In most forest (Tamias spp.), American Robin (Turdus migra- types, canopy cover around the nest tree is usually torius), Northern Flicker (Colaptes auratus), and >60%–100%, although it is about 25%–40% in Steller’s Jay (Cyanocitta stelleri). In the Lake Tahoe the naturally more open Pacific Ponderosa and region of the Sierra Nevada, annual variation in Jeffrey pine forests east of the Cascade-Sierra axis. goshawk reproduction is associated with late win- Goshawks usually place their stick nests in some of ter and early spring temperatures and abundance the larger available trees or, rarely, in snags. Nests of Douglas , which vary annually in con- are constructed mainly in the lower one-third of cordance with cone crop production (Keane 1999, nest trees or just below the forest canopy, with Keane et al. 2006). nest heights varying with tree species and regional Goshawks forage in mature and old-growth tree-height characteristics (Squires and Reynolds forests that have relatively dense canopies (Widen 1997). Of a sample of 157 nests in the southern 1989, Austin 1993, Bright-Smith and Mannan Cascades and western Sierra Nevada of California, 1994, Hargis et al. 1994, Iverson et al. 1996, 45% were placed in a deformed top or mistletoe Beier and Drennan 1997), but also capture prey clump, 43% against the trunk, and 12% out on in a variety of vegetative cover, including meadow a limb (Richter 2005). The diameter of trees in edges and open sagebrush (Younk and Bechard which nests were placed in deformities averaged 1994). Foraging habitat use probably varies sea- smaller than those where nests were against the sonally in response to prey availability. trunk or on a limb. Northern Goshawks are top-trophic-level pred- Woodbridge and Detrich (1994) reported that ators that have relatively large spatial requirements annual territory reoccupancy rates approached and occur at relatively low breeding densities. 100% when approximately 80 ha of suitable nest- Populations are likely regulated by a combination stand habitat was available. These rates decrease of territorial behavior, available prey, and suitabil- with smaller stand sizes indicative of forest frag- ity of nesting habitat. Although breeding pairs are mentation or management for limited buffers more or less regularly distributed within appropri- around nests (Woodbridge and Detrich 1994, ate habitat, breeding densities appear to vary with Richter 2005). patterns of habitat quality across the landscape Breeding-period home ranges of individuals in (Newton 1979, Joy 2002). Thus, landscapes can the Sierra Nevada averaged about 1800–2600 ha support only a certain, limited number of ter- (range = about 800–6200 ha: 95% adaptive kernel; ritories, and the spatial distribution of habitat is Hargis et al. 1994, Keane 1999). Nonbreeding- important for maintaining Northern Goshawk period home ranges averaged about 5500 ha populations. (range = 1400–12,100 ha) for females and 8200 ha (range = 1500–15,000 ha: 95% adaptive kernel) Threats for males (Keane 1999). In the southern Cascades, breeding-period home ranges averaged about 2400 Habitat loss and degradation are the primary ha (range = 1000–3900 ha) for males and about known threats to Northern Goshawks (Squires 3800 ha (range = 2000–6900 ha: 100% minimum and Kennedy 2006). As a result of timber harvest convex polygon) for females (Austin 1993). and fire suppression policies over the past century,

Northern Goshawk 159 Studies of Western Birds No. 1 contemporary California forests are strikingly conry in California. Current harvest levels do not different in structure, composition, and function affect statewide population numbers, although compared to the range of forest conditions result- negative effects may occur locally if specific breed- ing from the historic, natural disturbance regime. ing territories or areas, such as those on the Inyo These recent management policies have likely National Forest in the eastern Sierra Nevada, are degraded goshawk habitat quality by fragmenting repeatedly harvested. Pesticides are not known forests, reducing the amount and distribution of to have negatively affected Northern Goshawk mature and old-growth forest stands and large populations (Snyder et al. 1973, Squires and trees, increasing understory tree density, and Reynolds 1997), and no information is available changing tree species composition, resulting in to suggest current problems with contaminants broad-scale reduction of the proportion of pine in (see summary in Squires and Kennedy 2006). The forest stands. Nest sites and territories have been spread of West Nile virus to California in 2003, lost from logging in nest stands and from stand- and the susceptibility of other raptors to its effects, replacement fires. There is also increased risk of suggests goshawks may be at risk; still, there is loss of habitat to such fires because past manage- no strong evidence indicating any diseases are ment policies have increased fuel loads. significant factors limiting goshawk populations Past and current management standards and (Reynolds et al. 2006b). guidelines for goshawks focus on protecting habi- tat at nest sites during project implementation. Management and Research Management practices for nest territories on Recommendations private forestlands in California range from pro- tection of the nest tree and a few shade trees in • Regarding private and state lands, consult the general area of the nest tree to protection of with the Department of Fish and Game to 2–8 ha around the nest tree. Little or no protec- develop site-specific protection measures tion was directed at goshawk nest sites on U.S. around nest trees, including maintenance of Forest Service lands until 20–25 years ago. Since alternative nest trees. Restrict activities dur- then, management has varied among individual ing the critical nesting and fledgling periods national forests, with a focus on protection of (1 Mar–15 Aug). 20–80 ha around known goshawk nest sites. It • Review private and public land management is likely that many of these management prac- standards and guidelines to incorporate new tices are inadequate for maintaining long-term site information and evaluate their adequacy as occupancy (see Richter 2005 on private timber- applied to these lands. lands). Woodbridge and Detrich (1994) reported • Establish, annually update, and manage a that short-term reoccupancy rates approached statewide nesting record database for track- 100% for core areas that had approximately 80 ha ing distributional patterns and assessing of suitable nesting habitat. Standards and guide- conservation status across state, federal, and lines adopted for Sierra Nevada forests as part privately managed lands. of the Sierra Nevada Framework Project amend • Conduct specialized inventories to assess existing land management plans and require pro- distributional status in poorly known tection of the best available 80 ha of suitable nest- areas, such as the mountains of southern ing habitat around occupied nest sites. Northwest California. Forest Plan reserves provide protection for addi- • Conduct radiotelemetry studies to increase tional territories in limited areas of northern understanding of foraging habitat and prey California. Uncertainty exists regarding the effects use in both the breeding and winter peri- of proposed timber harvest and fuels management ods. strategies on goshawk habitat quality at the home • Conduct basic demographic research to range and landscape scales. understand how survival and reproduction Ongoing population growth and asso- are affected by interactions among habitat, ciated development and recreational activity, par- prey, weather, and, possibly, disease such as ticularly on the west slope of the Sierra Nevada West Nile virus. (see Stein et al. 2005), may result in further • Initiate collaboration between research and degradation of goshawk habitat quality through management in an adaptive management direct loss of habitat, increased disturbance from framework to assess the effects of forest and recreational activities, and elevated fire risk from fuels management policies on Northern human ignitions. Goshawks are harvested for fal- Goshawk territory occupancy, demograph-

160 Species Accounts California Bird Species of Special Concern

ics, and habitat quality, placing questions use by breeding male Northern Goshawks in northern within the larger context of the restoration Arizona. Studies Avian Biol. 16:58–65. of California forests and natural disturbance Brown, L., and Amadon, D. 1968. Eagles, Hawks and regimes. Variation across major California Falcons of the World. McGraw-Hill, New York. forest types in terms of forest structure, California Department of Fish and Game (CDFG). composition, function, patch size and dis- 1992. Bird species of special concern. Unpublished tribution, prey populations, and natural dis- list, July 1992, Calif. Dept. Fish & Game, 1416 Ninth turbance regimes dictates that management St., Sacramento, CA 95814. and conservation efforts be developed at Doyle, F. I., and Smith, J. M. N. 2001. Raptors and appropriate spatial scales. (See Reynolds et scavengers, in Ecosystem Dynamics of the Boreal al. 2006a for recommendations for develop- Forest: The Kluane Project (C. J. Krebs, S. Boutin, and R. Boostra, eds.), pp. 377–404. Oxford Univ. ing ecosystem-based conservation strategies Press, New York. for goshawks.) Franklin, J. F., and Fites-Kaufmann, J. A. 1996. Assess- ment of late-successional forests of the Sierra Nevada, onitoring eeds M N in Sierra Nevada Ecosystem Project, final report to The Breeding Bird Survey and Christmas Bird Congress, vol. II, Assessments and scientific basis Count are inadequate for monitoring population for management options, pp. 627–669. Univ. Calif. trends of goshawks (Squires and Kennedy 2006). Davis, Centers for Water and Wildland Resources. Available at http://ceres.ca.gov/snep/pubs/. Monitoring of Northern Goshawks in California will require the use of standardized protocols to Garrett, K., and Dunn, J. 1981. Birds of Southern Cali- fornia: Status and Distribution. Los Angeles Audubon assess population distribution, status, and trends Soc., Los Angeles. at appropriate spatial scales (e.g., Sierra Nevada Grinnell, J., and Miller, A. H. 1944. The distribution of bioregion). If feasible, monitoring in California the birds of California. Pac. Coast Avifauna 27. should follow the U.S. Forest Service’s recently Hall, P. A. 1984. Characterization of nesting habitat of developed design for bioregional monitoring of Goshawks (Accipiter gentilis) in northwestern Califor- population trends and their association, if any, nia. M.S. thesis, Humboldt State Univ., Arcata, CA. with broad-scale habitat changes (Hargis and Hargis, C. D., McCarthy, C., and Perloff, R. D. 1994. Woodbridge 2006). Empirically derived habitat Home ranges and habitats of Northern Goshawk in models should be used to monitor change in eastern California. Studies Avian Biol. 16:66–74. habitat distribution and quality at home-range Hargis, C. D., and Woodbridge, B. 2006. A design for and landscape scales. Monitoring project-level monitoring Northern Goshawks at the bioregional responses of nesting goshawks to management scale. Studies Avian Biol. 31:274–287. treatments would also be valuable. Howell, S. N. G., and Webb, S. 1995. A Guide to the Birds of Mexico and Northern Central America. Acknowledgments Oxford Univ. Press, Oxford. The account was improved by comments or unpub- Iverson, G. C., Hayward, G. D., Titus, K., DeGayner, lished data provided by T. Heindel, D. Richter, W. D. E., Lowell, R. E., Crocker-Bedford, D. C., Schempf, Shuford, and B. Woodbridge. P. F., and Lindell, J. 1996. Conservation assessment for the Northern Goshawk in southeast Alaska. Gen. Literature Cited Tech. Rep. PNW-GTR-387, U.S. Forest Serv., Pac. Northwest Res. Station, Portland, OR. American Ornithologists’ Union (AOU). 1957. Check- Joy, S. M. 2002. Northern Goshawk habitat on the Kai- list of North American Birds, 5th ed. Am. Ornithol. bab National Forest in Arizona: Factors affecting nest Union, Baltimore. locations and territory quality. Ph.D. dissertation, Austin, K. K. 1993. Habitat use and home range size of Colorado State Univ., Fort Collins. breeding Northern Goshawks in the southern Cas- Keane, J. J. 1999. Ecology of the Northern Goshawk cades. M.S. thesis, State Univ., Corvallis. in the Sierra Nevada, California. Ph.D. dissertation, Beier, P., and Drennan, J. E. 1997. Forest structure and Univ. Calif., Davis. prey abundance in foraging areas of Northern Gos- Keane, J. J., Morrison, M. L., and Fry, D. M. 2006. Prey hawks. Ecol. Applications 7:564–571. and weather factors associated with temporal varia- Bloom, P. H., Stuart, G. R., and Walton, B. J. 1986. tion in Northern Goshawk reproduction in the Sierra The status of the Northern Goshawk in California, Nevada, California. Studies Avian Biol. 31:85–99. 1981–1983. Wildl. Mgmt. Branch Admin. Rep. 85- Kiff, L. F., and Paulson, D. R. 1997. Northern Goshawk 1, Calif. Dept. Fish & Game, Sacramento. breeding records from San Diego County, California. Bright-Smith, D. J., and Mannan, R. W. 1994. Habitat W. Birds 28:113–114.

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Lentz, J. E. 1993. Breeding birds of four isolated moun- Snyder, N. F. R., Snyder, H. A., Lincer, J. L., and Reyn- tains in southern California. W. Birds 24:201–234. olds, R. T. 1973. Organochlorines, heavy metals, and Maurer, J. R. 2000. Nesting habitat and prey relations the biology of North American accipiters. BioScience of the Northern Goshawk in Yosemite National Park, 23:300–305. California. M.S. thesis, Univ. Calif., Davis. Squires, J. R., and Kennedy, P. L. 2006. Northern Gos- McCoy, R. H. 1999. Effects of prey delivery on the hawk ecology: An assessment of current knowledge fledgling success of Northern Goshawks. M.S. thesis, and information needs for conservation and manage- Humboldt State Univ., Arcata, CA. ment. Studies Avian Biol. 31:8–62. Newton, I. 1979. Population Ecology of Raptors. Buteo Squires, J. R., and Reynolds, R. T. 1997. Northern Books, Vermillion, SD. Goshawk (Accipiter gentilis), in The Birds of North Remsen, J. V., Jr. 1978. Bird species of special concern America (A. Poole and F. Gill, eds.), no. 298. Birds in California: An annotated list of declining or vul- N. Am., Philadelphia. nerable bird species. Nongame Wildl. Invest., Wildl. Stein, S. M., McRoberts, R. E., Alig, R. J., Nelson, M. Mgmt. Branch Admin. Rep. 78-1, Calif. Dept. Fish & D., Theobald, D. M., Eley, M., Dechter, M., and Game, 1416 Ninth St., Sacramento, CA 95814. Carr, M. 2005. Forests on the edge: Housing devel- Reynolds, R. T., Graham, R. T., and Boyce, D. A., opment on America’s private forests. Gen. Tech. Rep. Jr. 2006a. An ecosystem-based conservation strat- PNW-GTR-636, U.S. Forest Serv., Pac. Northwest egy for the Northern Goshawk. Studies Avian Biol. Res. Station, Portland, OR. Available at www.fs.fed. 31:299–311. us/projects/fote/reports/fote-6-9-05.pdf. Reynolds, R. T., Wiens, J. D., and Salafsky, S. R. Unitt, P. 2004. San Diego County bird atlas. Proc. San 2006b. A review and evaluation of factors limiting Diego Soc. Nat Hist. 39. Northern Goshawk populations. Studies Avian Biol. Weber, T. T. 2006. Northern Goshawk (Accipiter genti- 31:260–273. lis) nesting habitat in northwestern California. An Richter, D. J. 2005. Territory occupancy, reproductive examination of three spatial scales: The nest area, success, and nest site characteristics of goshawks on the post-fledging area, and the home range. M.S. managed timberlands in central and northern Califor- thesis, Humboldt State Univ., Arcata, CA. Available nia 1993–2000. Calif. Fish Game 91:100–118. at http://dscholar.humboldt.edu:8080/dspace/bit- stream/2148/145/1/Final+draft5.pdf. Sauer, J. R., Hines, J. E., and Fallon, J. 2005. The North American Breeding Bird Survey, results and analysis Widen, P. 1989. The hunting habitats of Goshawks Ac- 1966–2004, version 2005.2. USGS Patuxent Wildl. cipiter gentilis in boreal forests of central Sweden. Ibis Res. Ctr., Laurel, MD. Available at www.mbr-pwrc. 131:205–213. usgs.gov/bbs/bbs.html. Woodbridge, B., and Detrich, P. J. 1994. Territory oc- Sauer, J. R., Schwartz, S., and Hoover, B. 1996. The cupancy and habitat patch size of Northern Goshawks Christmas Bird Count home page, version 95.1. in the southern Cascades of California. Studies Avian USGS Patuxent Wildl. Res. Ctr, Laurel, MD. Avail- Biol. 16:83–87. able at www.mbr.nbs.gov/bbs/cbc.html. Younk, J. V., and Bechard, M. J. 1994. Breeding ecology Saunders, L. B. 1982. Essential nesting habitat of the of the Northern Goshawk in high-elevation aspen Goshawk (Accipiter gentilis) on the Shasta-Trinity forests of northern Nevada. Studies Avian Biol. National Forest, McCloud District. M.S. thesis., 16:119–121. Calif. State Univ., Chico.

162 Species Accounts