The American goshawk ( Astur atricapillus) is a species of raptor in the family Accipitridae. It was first described by Alexander Wilson in 1812. The American goshawk was previously considered conspecific with the Eurasian goshawk but was assigned to a separate species in 2023 based on differences in morphology, vocalizations, and genetic divergence.[ It was formerly placed in the genus Accipiter. It is mainly resident bird, but birds from colder regions bird migration south for the winter.]
Distribution
In North America, they are most broadly found in the Western United States, including Alaska, and western Canada. Their breeding range in the western contiguous United States largely consists of the wooded foothills of the Rocky Mountains and many other large mountain ranges from Washington to southern California extending east to central Colorado and westernmost Texas.[Monson, G. & Phillips, A. R. (1964). A check-list of the birds of Arizona. Tucson: Univ. of Arizona Press.][Howell, S. N. G. & Webb, S. (1995). A guide to the birds of Mexico and northern Central America. New York: Oxford University Press. ]
The goshawk continues east through much of Canada as a native species, but is rarer in most of the Eastern United States, especially the Midwest, where they are not typically found outside the Great Lakes region, where a good-sized breeding population occurs in the northern parts of Minnesota, Illinois, Michigan, and somewhat into Ohio; a very small population persists in the extreme northeast corner of North Dakota. They breed also in mountainous areas of New England, New York, central Pennsylvania, and northwestern New Jersey, sporadically down to extreme northwestern Maryland and northeastern West Virginia.
Habitat
American and Eurasian goshawks can be found in both deciduous and coniferous Temperate forest. While the species might show strong regional preferences for certain trees, they seem to have no strong overall preferences nor even a preference between deciduous or coniferous trees despite claims to the contrary.[Erickson, M. G. (1987). Nest site habitat selection of the goshawk (Accipiter gentilis) in the Black Hills of South Dakota (Doctoral dissertation, MS thesis. University of South Dakota. Brookings, South Dakota).]
Access to Wetland and of any kind is not uncommon in goshawk home ranges but seems to not be a requirement.[ In winter months, the northernmost or high mountain populations move down to warmer forests with lower elevations, often continuing to avoid detection except while migrating. A majority of goshawks around the world remain sedentary throughout the year.]
Description
Similar species
The juvenile plumage of the species may cause some confusion, especially with other juvenile Astur species. Unlike other northern Astur, the adult American and Eurasian goshawk never has a rusty color to its underside barring.[Cramp, S. and K. E. L. Simmons. (1980). Handbook of the birds of Europe and the Middle East and North Africa: the birds of the western Palearctic, Vol. 2. Hawks to bustards. Oxford: Oxford Univ. Press. ][Kaufman, K. (1990). A Field Guide to advanced birding: birding challenges and how to approach them. Boston, MA: Houghton Mifflin Co. ]
American goshawks are sometimes mistaken for species even outside of the genus Astur especially as juveniles of each respective species. In North America, four species of Buteoninae (all four of which are smaller than goshawks to a certain degree) may be confused with them on occasion despite the differing proportions of these hawks, which all have longer wings and shorter tails relative to their size. A species so similar it is sometimes nicknamed the "Mexican goshawk", gray hawk ( Buteo plagiatus) juveniles (overlapping with true goshawks in the southwest United States into Mexico) have contrasting face pattern with bold dusky eye-stripes, dark eyes, barred thighs and a bold white "U" on the uppertail coverts. The roadside hawk ( Rupornis magnirostris) (rarely in same range in Mexico) is noticeably smaller with paddle-shaped wings, barred lower breast and a buff “U” on undertail coverts in young birds. Somewhat less likely to confuse despite their broader extent of overlap are the red-shouldered hawk ( Buteo lineatus) which have a narrow white-barred, dark-looking tail, bold white crescents on their primaries and dark wing edges and the broad-winged hawk ( Buteo playpterus) which also has dark wing edges and a differing tapered wing shape. Even wintering gyrfalcon ( Falco rusticolus) juveniles have been mistaken for goshawks and vice versa on occasion, especially when observed distantly perched. However, the bulkier, broader headed yet relatively shorter tailed falcon still has many tell-tale falcon characteristics like pointed, longer wings, a brown malar stripe as well as its more extensive barring both above and below.[
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Juveniles are sometimes confused with the smaller Cooper's hawk ( Astur cooperii), especially juvenile Cooper's hawks. Unlike in Europe with sparrowhawks, Cooper's hawks can have a largish appearance and juveniles may be regularly mistaken for the usually less locally numerous goshawk. However, the juvenile goshawk displays a heavier, vertical streaking pattern on chest and abdomen, with the juvenile Cooper's hawk streaking frequently (but not always) in a “teardrop” pattern wherein the streaking appears to taper at the top, as opposed to the more even streaking of the goshawk. The goshawk sometimes seems to have a shorter tail relative to its much broader body. Although there appears to be a size overlap between small male goshawks and large female Cooper's hawks, morphometric measurements (wing and tail length) of both species demonstrate no such overlap, although weight overlap can rarely occur due to variation in seasonal condition and food intake at time of weighing.[.]
Taxonomy
The genus Astur contains nine living species. This group of agile, smallish, forest-dwelling hawks has been in existence for possibly tens of millions of years, probably as an adaptation to the explosive numbers of small birds that began to occupy the world's forest in the last few eras. The harriers are the only group of extant diurnal raptors that seem to bear remotely close relation to this genus, whereas Buteoninae, Milvinae, and Melierax are much more distantly related and all other modern accipitrids are not directly related.
Within the genus Astur, the American goshawk seems to belong to a Species complex with other larger goshawks from different portions of the world.[Kleinschmidt, O. (1923). Berajah, Zoografia infinita. Die Realgattung Habicht, Falco columbarius (KL). Gebauer-Schwetschke, Halle, Germany.] Eurasian goshawk, found in Eurasia, was previously considered conspecific with American goshawk, formed the species complex "northern goshawk". Meyer's goshawk, found in the South Pacific, has been posited as the most likely to be the closest related living cousin to the northern goshawk, the somewhat puzzling gap in their respective ranges explained by other Palearctic raptors such as Bonelli's eagles ( Aquila fasciata) and ( Circaetus gallicus) that have extant isolated tropical island populations and were probably part of the same southwest Pacific radiation that led to the Meyer's goshawk.[.] A presumably older radiation of this group may have occurred in Africa, where it led to both the Henst's goshawk of Madagascar and the black sparrowhawk ( Astur melanoleucus) of the mainland. While the Henst's goshawk quite resembles the northern goshawks, the black sparrowhawk is superficially described as a “sparrowhawk” due to its relatively much longer and finer legs than those of typical goshawks but overall its size and plumage (especially that of juveniles) is much more goshawk than sparrowhawk-like.
Genetic studies have indicated that the Cooper's hawk of North America is also fairly closely related to the northern goshawk, having been present in North America before either of the other two North American Accipiters. However, the much smaller sharp-shinned hawk, which has similar plumage to the Cooper's hawk and seems to be most closely related to the Eurasian sparrowhawk, appears to have occupied North America the latest of the three North American species, despite having the broadest current distribution of any Astur in the Americas (extending down through much of South America).
Subspecies
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A. a. atricapillus (Wilson, 1812) – This subspecies occupies a majority of the species' range in North America, excluding some islands of the Pacific Northwest and the southern part of the American Southwest. American goshawks are generally slightly smaller on average than most Eurasian ones, although there are regional differences in size that confirm mildly to Bergmann's rule within this race. Furthermore, sexual dimorphism in size is notably less pronounced in American goshawks than in most Eurasian races. Overall, the wing chord is in males and in females.
[ Size within atricapillus based on body mass seems to be highest in interior Alaska, followed by the Great Lakes, is intermediate in the northwest United States from eastern Washington to the Dakotas as well as in southeast Alaska thence decreasing mildly along the Pacific in Oregon and California and smallest of all within the race in the Great Basin and Colorado Plateau states (i.e. Nevada, Utah and northern and central Arizona). Conspicuously, wing size did not correspond to variations in body mass and more southerly goshawks were frequently longer winged than the more massive northerly ones.][Smith, J. P., Hoffman, S. W., & Gessaman, J. A. (1990). Regional Size Differences among Fall-Migrant Accipiters in North America. Journal of Field Ornithology, 192–200.][Whaley, W. H. & White, C.M. (1994). Trends in geographic variation of Cooper's hawk and northern goshawk in North America: a multivariate analysis. Proc. West. Found. Vertebr. Zool. no. 5:161-209.] Male atricapillus goshawk have been found to weigh from and females from .[Dunning Jr., John B. (ed.) (2008). CRC Handbook of Avian Body Masses, 2nd Edition. CRC Press. .][Henny, C. J., Olson. R. A. & Fleming, T. L. (1985). Breeding chronology, molt, and measurements of accipiter hawks in northeastern Oregon. J. Field Ornithol. no. 56: 97–112.] The lightest reported mean weights were from goshawks in northern and central Arizona, weighing a mean of in males and while the highest were from a small sample of Alaskan goshawks which weighed some in males and in females.[Mavrogordato, J. (1973). A Hawk for the Bush: A Treatise on the Training of the Sparrow-hawk and Other Short-winged Hawks. Spearman.][Mueller, H. C., Berger, D. D. & Allez, G. (1976). Age and sex variation in the size of goshawks. Bird-Banding no. 47 (4):310–318.] Almost identical mean weights for goshawks as in Alaska were recorded for goshawks from Alberta as well.[ This race is typically a blue-gray color above with a boldly contrasting black head and broad white supercilia. American goshawks are often grayish below with fine gray waving barring and, compared to most Eurasian goshawks, rather apparent black shaft streaks which in combination create a vermiculated effect that is all-together messier looking than in most Eurasian birds. From a distance, atricapillus can easily appear solidly all-gray from the front.][ Due to this, the adult goshawk in America is sometimes called the “gray ghost”, a name also somewhat more commonly used for adult male .][Rashid, S. (2015). Northern Goshawk, the Grey Ghost: Habits, Habitats and Rehabilitation. Schiffer Publishing Ltd.] Birds from mainland Alaska tend to be paler overall with more pale flecking than other American goshawks.
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A. a. laingi Tavernier, 1940 – This insular race is found on Haida Gwaii and Vancouver Island. This subspecies is slightly smaller than the goshawks found on the mainland and is linearly the smallest race on average in North America. The wing chord of males can range from and that of females is and is on average nearly 5% smaller than those sampled goshawks from the nearby mainland.
[Iverson, G. C., Hayward, G. D., Titus, K. DeGayner, E., Lowell, R. E., Crocker-Bedford, D. C., Schempf, P. F. & Lindell, J. F. (1996). Conservation assessment for the northern goshawk in southeast Alaska. U.S. Dept., Agric., For. Serv. Publ.]
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A. a. apache (van Rossem, 1938) – The range of this subspecies extends from southern Arizona and New Mexico down throughout the species' range in Mexico. This subspecies has the longest median wing size of any race, running contrary to Bergmann's rule that northern birds should outsize southern ones in widely distributed temperate species. In males the wing chord ranges from while in females it ranges from .
[ However, in terms of body mass, it is only slightly heavier than the goshawks found discontinuously somewhat to the north in the Great Basin and the Colorado Plateau and lighter than the heaviest known American goshawks from Alaska, Alberta and Wisconsin despite exceeding the goshawks from these areas in wing size. The weight of 49 males ranged from , averaging , while that of 88 females from two studies ranged from , averaging .][Ingraldi, M.F. (2005). A skewed sex ratio in Northern Goshawks: is it a sign of a stressed population? Journal of Raptor Research 39.3 (2005): 247–252.] Aside from its overall larger size, apache reportedly averages larger in foot size than most other American goshawks. Birds of this race tend to be darker than other American goshawks aside from the laingi type birds. Due to its shortage of distinct features beyond proportions, this is considered one of the more weakly separated among current separate subspecies, with some authors considering it merely a clinal variation of atricapillus. Even the greater wing size in southern birds follows a trend for the wing chord to increase in size in the south on the contrary to body mass.[
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Behavior
Migration
Migratory goshawks in North America may move down to Baja California, Sinaloa and into most of west Texas, but generally in non-irruptive years, goshawks winter no further south than Nebraska, Iowa, Illinois, Indiana, eastern Tennessee and western North Carolina.[Keane, J. J. & Morrison, M.L. (1994). "Northern Goshawk ecology: effects of scale and levels of biological organization". Stud. Avian Biol. no. 16:3-11.] Some periodic eruptions to nearly as far as the Gulf of Mexico have been recorded at no fewer than 10 years apart. In one case, a female that was banded in Wisconsin was recovered in Louisiana, a first ever record of the species in that state.[Evans, D. L. & Sindelar, C. R. (1974). "First record of the goshawk for Louisiana-a collected, banded bird"". Bird-Banding, no. 45: 270.]
Prey availability may primarily dictate the proportion of goshawk populations that migrate and the selection of wintering areas, followed by the presence of snow which may aid prey capture in the short-term but in the long-term is likely to cause higher goshawk mortality.[Marcström, V., & Kenward, R. (1981). Movements of wintering goshawks in Sweden. Swedish Sportsmen's Association.][Doyle, F. I. & Smith, J. M. N. (1994). "Population responses of northern goshawks to the 10-year cycle in numbers of snowshoe hares". Stud. Avian Biol. no. 16:122–129.] Showing the high variability of migratory movements, in one study of winter movements of adult female goshawks that bred in high-elevation forests of Utah, about 36% migrated to the general south, 22% migrated farther than that distance, 8.3% migrated less far, 2.7% went north instead of south and 31% stayed throughout winter on their breeding territory.[Mueller, H. C., D. D. Berger and G. Allez. 1977. "The periodic invasions of goshawks". Auk no. 94:652-663.] At the hawk watch at Cape May Point State Park in New Jersey, few adult males and no adult females have been recorded in fall migration apart from irruptive years, indicating that migration is more important to juveniles.[Sibley, D. A. 1997. Birds of Cape May, 2nd ed. Cape May Point: New Jersey Audubon Soc.] More juveniles were recorded migrating than adults in several years of study from Sweden.[Hoffman, S. W., W. R. DeRagon and J. C. Bednarz. (1992). Patterns and recent trends in counts of migrant hawks in western North America, 1977-1991. Unpubl. report.]
Dietary biology
Hunting behavior
In North America, goshawks are generally rather more likely than those from Eurasia to hunt within the confines of mature forest, excluding areas where prey numbers are larger outside of the forest, such as where scrub-dwelling are profuse.
Prey spectrum
Northern goshawks are usually opportunistic predators, as are most birds of prey. The most important prey species are small to medium-sized and medium to large-sized birds found in forest, edge and scrub habitats.
However, a few prey families dominate the diet in most parts of the range, namely , , grouse, Phasianidae, thrushes and (in roughly descending order of importance) among birds and (mainly but also especially in North America) and Leporidae among mammals.
Birds constitute 47.8% in 33 studies and mammals account for a nearly equal portion of the diet and in some areas rather dominate the food spectrum.[Kennedy, P. L. (2003). Northern goshawk (Accipiter gentilis atricapillus): A technical conservation assessment. USFS, Rocky Mountain Region, Species Conservation Project. Fort Collins, Colorado.][Bosakowski, T. (1999). The Northern Goshawk: Ecology, Behavior and Management in North America. Hancock House Pub Limited.][Jones, S. (1979). The accipiters: goshawk, Cooper's hawk, sharp-shinned hawk (No. 17). US Dept. of the Interior, Bureau of Land Management.] There is some difference in size and type between the prey caught by males and larger females. Prey selection between sexes is more disparate in the more highly dimorphic races from Eurasia than those from North America. The average prey caught by each sex in Arizona was and , respectively, or around a 26% difference.[Boal, C. W., & Mannan, R. W. (1996). Prey sizes of male and female northern goshawks. The Southwestern Naturalist, 355–358.]
Corvids
Overall, one prey family that is known to be taken in nearly every part of the goshawk's range is the corvids, although they do not necessarily dominate the diet in all areas. Some 24 species have been reported in the diet of Eurasian and American goshawks. The second most commonly reported prey species in breeding season dietary studies from North America is the Steller's jay ( Cyanocitta stelleri). These species were recorded in studies from northwestern Oregon and the Kaibab Plateau of Arizona (where the Steller's made up 37% by number) as the main prey species by number. The conspicuously loud vocalizations, somewhat sluggish flight (when hunting adult or post-fledging individuals) and moderate size of these jays make them ideal for prey-gathering male goshawks.[Karyakin, I. (2009). Goshawk in the Urals and adjacent territories. Raptor Conservation, A (4).]
Pigeons and doves
Most of American goshawks take pigeons less commonly than Eurasian goshawks.
Gamebirds
The American goshawk is in some parts of its range considered a specialized predator of Galliformes, particularly grouse. All told 33 species of this order have turned up in American and ' diet, including most of the species either native to or introduced in North America and Europe. Numerically, only in the well-studied taiga habitats of Canada and Alaska and some areas of the eastern United States do grouse typically take a dominant position. Elsewhere in the range, gamebirds are often secondary in number but often remain one of the most important contributors of prey biomass to nests. With their general ground-dwelling habits, gamebirds tend to be fairly easy for goshawks to overtake if they remain unseen and, if made aware of the goshawk, the prey chooses to run rather than fly. If frightened too soon, gamebirds may take flight and may be chased for some time, although the capture rates are reduced considerably when this occurs. Pre-fledgling chicks of gamebirds are particularly vulnerable due to the fact that they can only run when being pursued.
Despite reports that grouse are less significant as prey to American goshawks, the ruffed grouse ( Bonasa umbellus) is one of the most important prey species in North America (fourth most reported prey species in 22 studies), having been the leading prey species for goshawks in studies from New York, New Jersey and Connecticut (from 12 to 25% of prey selected) and reported as taken in high numbers elsewhere in several parts of their mutual range.[Graham, R. T., de Volo, S. B., & Reynolds, R. T. (2015). Northern goshawk and its prey in the Black Hills: Habitat assessment. Gen. Tech. Rep. RMRS-GTR-339. Fort Collins, CO: US, Department of Agriculture, Forest Service, Rocky Mountain Research Station.] The sooty grouse ( Dendragapus fuliginosus) was reported as the leading prey species in southern Alaska (28.4% by number).[The Shipley Group (2009). Goshawk Survey; Soule River Watershed, Southeast Alaska. Alaska Power & Telephone Survey.] In the boreal forests of Alberta, grouse are fairly important prey especially in winter.[Schaffer, W. W. 1998. Northern goshawk (Accipiter gentilis) habitat characterization in central Alberta. Thesis, University of Alberta, Edmonton, Alberta.]
Squirrels
In North America, tree squirrels are even more significant as prey, particularly the modestly-sized which are the single most important prey type for American goshawks overall. Particularly the American red squirrel ( Tamiasciurus hudsonicus) is significant, being the primary prey in studies from Minnesota, South Dakota, Wyoming and Montana (in each comprising more than 30% of the diet and present in more than half of known pellets) but also reported everywhere in their foods from the eastern United States to Alaska and Arizona. Much like the American marten ( Martes americana), the American distribution of goshawks is largely concurrent with that of American red squirrels, indicating the particular significance of it as a dietary staple.[Schaffer, W. W. 1998. Northern goshawk (Accipiter gentilis) habitat characterization in central Alberta. Thesis, University of Alberta, Edmonton, Alberta.][Graham, R. T., de Volo, S. B., & Reynolds, R. T. (2015). Northern goshawk and its prey in the Black Hills: Habitat assessment. Gen. Tech. Rep. RMRS-GTR-339. Fort Collins, CO: US, Department of Agriculture, Forest Service, Rocky Mountain Research Station.][Clough, L. T. (2000). Nesting habitat selection and productivity of northern goshawks in west-central Montana. University of Montana.] In the Pacific Northwest, the Douglas squirrel ( Tamiasciurus douglasii) replaces the red squirrel in both distribution and as the highest contributor to goshawk diets from northern California to British Columbia. The largest occurrence of Douglas squirrel known was from Lake Tahoe, where they constituted 23% of prey by number and 32.9% by weight.[Promessi, R. L., Matson, J. O., & Flores, M. (2004). Diets of nesting northern goshawks in the Warner Mountains, California. Western North American Naturalist, 359–363.]
Larger tree squirrels are also taken opportunistically, in New York, New Jersey and Connecticut, the eastern gray squirrel ( Sciurus carolinensis) was the third most significant prey species.[.][Reynolds, R. T. & Meslow, E. C. (1984). Partitioning of food and niche characteristics of coexisting Accipiter during breeding. Auk no. 101:761–779.][Feldhamer, G. A., Thompson, B. C., & Chapman, J. A. (2003). Wild mammals of North America: biology, management, and conservation. JHU Press.][Slobodchikoff, C.; B. Perla; J. Verdolin (2009). Prairie Dogs: Communication and Community in an Animal Society. Cambridge, Massachusetts: Harvard University Press.] Several ( Marmota caligala) were brought to nests in southeast Alaska but averaged only , so were young animals about half of the average adult (spring) weight (albeit still considerably heavier than the goshawks who took them).[Verts, B. J., & Carraway, L. N. (2001). Tamias minimus. Mammalian Species, 1-10.]
Hares and rabbits
Mammals are more important in their diet than in Eurasian goshawk's, more lagomorphs are taken. In Oregon, ( Lepus americanus) are the largest contributor of biomass to goshawks foods (making up to 36.6% of the prey by weight), in eastern Oregon at least 60% of hares taken were adults weighing on average , and in one of three studies from Oregon be the most numerous prey species (second most numerous in the other two).[ This species was also the second most numerous food species in Alberta throughout the year and the most important prey by weight.][ Eastern cottontails ( Sylvilagus floridanus), also averaging some in mass per the study (and thus mostly consisting of adult cottontails in their prime), were the most significant prey both by weight (42.3%) and number (13.3%) in Apache-Sitgreaves National Forest of Arizona. Eastern cottontails are also taken regularly in New York and Pennsylvania.][Chapman, J. A., & Flux, J. E. (1990). Rabbits, hares and pikas: status survey and conservation action plan. IUCN.] American goshawks also take , much smaller cousins of rabbits and hares, but they are at best supplementary prey for American goshawks.[
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Other birds
Some 21 species of woodpecker have been reported from northern goshawk food studies around the world. With their relatively slow, undulating flight adult and fledged woodpeckers can easily be overtaken by hunting goshawks, not to mention their habitat preferences frequently put them within active goshawk ranges. Most of the widespread species from North America have been observed as prey, most commonly relatively large woodpeckers such as the northern flicker ( Colaptes auratus) in North America. Indeed, the flicker is the third most regularly reported prey species in America.[Schreven, K. Een luchtbukskogeltje in een braakbal van een Havik Accipiter gentilis, in de context van jacht en loodvergifti-ging. De Takkeling, 225–229.] In south-central Wyoming, the northern flicker was the second most numerous prey species and it was the main prey species in a study from New Mexico (here making up 26.4% of prey by number).[Kennedy, P. L. (1989). The nesting ecology of Cooper's hawks and northern goshawks in the Jemez Mountains, NM: a summary of results, 1984-1988 (Final Report). Santa Fe National Forest: U.S.D.A. Forest Service.] All sizes of woodpeckers available are taken from the downy woodpecker ( Picoides pubescens) to the pileated woodpecker ( Dryocopus pileatus) in North America.[Promessi, R. L., Matson, J. O., & Flores, M. (2004). Diets of nesting northern goshawks in the Warner Mountains, California. Western North American Naturalist, 359–363.] In many areas, American goshawks will pursue of several varieties, although they rarely form a large portion of the diet. Perhaps the most often recorded water birds in the diet are . All told, 32 waterfowl have been recorded in Eurasian and American goshawks' diet.[ Similarly, the wood duck ( Aix sponsa) frommay be more vulnerable than most waterfowl at their tree nests.][Opdam, P. F. M. (1980). Feeding ecology and niche differentiation in goshawk (Accipiter gentilis L.) and sparrowhawk (Accipiter nisus L.) (Doctoral dissertation, Sl: PFM Opdam).][Ivanovsky, V. V. (1998). Current status and breeding ecology of the Goshawk Accipiter gentilis in northern Belarus. Holarctic Birds of Prey, ADENEXWWGBP, Calamonte, Spain, 111–115.][Møller, A. P.; Solonen, T.; Byholm, P.; Huhta, E.; Tøttrup Nielsen, J. and Tornberg, R. 2012. "Spatial consistency in susceptibility of prey species to predation by two Accipiter hawks". J. Avian Biol. 43.][Nethersole-Thompson, D. (2010). Waders: their breeding, haunts and watchers. A&C Black.]
Corvids as aforementioned are quite important prey. Although they take fewer passerines than other northern Accipiters, smaller types of songbirds can still be regionally important to the diet. This is especially true of the thrushes.[/> Smaller numbers of thrush are taken in general but the [[American robin]] (''Turdus migratorius'') are fairly regular prey nonetheless and were the most numerous prey in the Sierra Nevadas of [[California]] (30.7% by number and 21.4% by weight).][ Beyond corvids and thrushes, most passerines encountered by American goshawks are substantially smaller and are often ignored under most circumstances in favor of more sizable prey. Nonetheless, more than a hundred passerines have been recorded their diet beyond these families. Most widespread passerine families from North America and Europe have occasional losses to goshawks, including tyrant flycatchers, [[shrike]]s, [[vireo]]s, [[lark]]s, [[swallow]]s, [[nuthatch]]es, [[treecreeper]]s, [[mimid]]s, [[pipit]]s and [[wagtail]]s, [[starling]]s, New World warblers, [[cardinalids|Cardinalidae]], [[icterid]]s, [[finch]]es. Avian prey has even ranged to as small as the [[goldcrest]] (''Regulus regulus''), the smallest bird in Europe.][ Among smaller types of passerines, one of the most widely reported are [[finch]]es and, in some widespread studies, somewhat substantial numbers of finches of many species may actually be taken. Finches tend to fly more conspicuously as they cover longer distances, often bounding or undulating as they do, over the canopy than most forest songbirds, which may make them more susceptible to goshawk attacks than other small songbirds.][Abuladze, A. (2013). ''Birds of Prey of Georgia''. Materials towards Fauna of Georgia, Issue VI, Institute of Zoology, Ilia State University.][Roberson, A. M., Anderson, D. E., & Kennedy, P. L. (2003). ''The northern goshawk (Accipiter gentilis atricapillus) in the western Great Lakes Region: a technical conservation assessment''. Minnesota Cooperative Fish and Wildlife Research Unit, University of Minnesota.]
Interspecies predatory relationships
Eurasian goshawks are often near the top of the avian food chain in forested biomes but face competition for food resources from various other predators. The mean prey mass for sharp-shinned and Cooper's hawks in North America is between about 10 and 30% of their own mass, whereas the mean prey of American goshawks is between about 25 and 50% of their mass and therefore are the goshawks takes prey that is on average relatively much larger.
In many of the ecosystems that they inhabit, American goshawks compete with resources with other predators, particularly where they take sizeable numbers of lagomorphs. About a dozen mammalian and avian predators in each area primarily consume alongside goshawks in the American boreal forest regions where these became primary staple foods. Like those cohabitant predators, the goshawk suffers declines during the low portion of the lagomorph's breeding cycles, which rise and fall cyclically every 10 years. However, even where these are primary food sources, the American goshawk is less specialized than many other raptors and can alternate their food selection, often taking equal or greater numbers of tree squirrels and woodland birds. Due to this dietary variation, the northern goshawk is less affected than other raptorial birds by prey population cycles and tends to not be depleted by resource competition.[Doyle, F. I. & Smith, J. M. N. (1994). "Population responses of northern goshawks to the 10-year cycle in numbers of snowshoe hares". Stud. Avian Biol. no. 16:122–129.]
Despite their propensity to pursue relatively large prey and capability to pursue alternate prey, American goshawks can be locally outcompeted for resources by species that are more adaptable and flexible, especially in terms of habitat and prey. Most northern buteonine hawks largely take small rodents such as (which are usually ignored by goshawks) but can adapt to nearly any other type of prey when the staple local rodent prey populations go down.[Marti, C. D., Korpimäki, E., & Jaksić, F. M. (1993). "Trophic structure of raptor communities: a three-continent comparison and synthesis". Current Ornithology, pp. 47–137. Springer US.] Comparisons with goshawks and red-tailed hawk nesting in abutting areas of Arizona (other large common Buteos like Swainson's hawks ( Buteo swainsonii) and ( Buteo regalis) utilize open habitats and so do not come into conflict with goshawks) shows the red-tailed hawks as being able to take a broader range of prey than goshawks and nest in more varied habitats, the latter species being perhaps the most commonly seen, widespread and adaptable of diurnal American raptors.[Preston, C. R. (2000). Red-tailed hawk. Stackpole Books.]
American goshawks are less prone to nesting outside of mature forests and take larger numbers of mammals as opposed to abundant birds than in Europe. This may be in part due to heavier competition from a greater diversity of raptors in North America. In Europe, the goshawk only co-exists with the much smaller sparrowhawk within its own genus, while in North America, it lives with the intermediately-sized Cooper's hawk. The latter species much more readily nests in semi-open and developed areas of North America than goshawks there and hunts a broad assemblage of medium-sized birds, whereas such prey is more readily available to male goshawks from Europe than to goshawks in North America. Although the Cooper's hawk usually avoids and loses individual contests against the larger goshawk, its adaptability has allowed it to become the most widespread and commonly found North American Accipiter.[Kenward, R. E. (1996). Goshawk Adaptation to Deforestation: Does Europe Differ From North. Raptors in Human Landscapes: Adaptation to Built and Cultivated Environments, 233.][Reynolds, R. T. & Wight, H. M. (1978). "Distribution, density, and productivity of accipiter hawks breeding in Oregon". The Wilson Bulletin, 182–196.]
American goshawks are slightly smaller on average than their European counterparts and can be up to 10% smaller in mass than red-tailed hawks. However, studies have indicated that the goshawk has, beyond its superior speed and agility, has stronger feet and a more forceful attack than that of the red-tailed hawk. All in all, individual competitions between red-tailed hawks and goshawks can go either way and neither is strongly likely to deter the other from nesting given their distinct nesting habitats.[Goslow, G. E. (1971). "The attack and strike of some North American raptors". The Auk, 815-827.][Sprunt, A., & May, J. B. (1955). North American birds of prey. Published under the sponsorship of the National Audubon Society by Harper.] Other raptors, including most medium to large-sized owls as well as red-tailed hawks and falcons, will use nests built by northern goshawks, even when goshawks are still in the area.
To many other raptorial birds, the northern goshawk is more significant as a predatory threat than as competition. American goshawk predate other accipiters such as the sharp-shinned hawk and the Cooper's hawk.[Becker, T. E.; Smith, D. G.; Bosakowski, T. (2006). "Habitat, food habits, and productivity of northern goshawks nesting in Connecticut". Studies in Avian Biology. 31: 119–125.][Smithers, B. L.; Boal, C. W.; Andersen, D. E. (2005). "Northern Goshawk diet in Minnesota: An analysis using video recording systems" (PDF). Journal of Raptor Research. 39 (3): 264–273.][Reynolds, R. T., Joy, S. M. & Leslie, D. G. (1994). "Nest productivity, fidelity, and spacing of northern goshawks in northern Arizona". Stud. Avian Biol. no. 16:106–113.]
Status
The breeding range of the American goshawk extends over one-third of North America, a total area of over for Eurasian and American goshawk. There are a broadly estimated 150,000–300,000 individuals in North America. most western populations at mid-latitudes have approximately 3.6–10.7 pairs/. A total of 107 nesting territories (1991–1996) were located on a study area on the Kaibab Plateau, AZ, resulting in a density of 8.4 pairs/. The estimated density in Pennsylvania (1.17 pairs/) suggests that eastern populations may occur at lower densities than western populations, but densities of eastern populations may increase as these populations recover. Typically, populations at far northern latitudes may occur at lower densities than those of southwestern and western populations in North America.[Kimmel, J. T. and R. H. Yahner (1994). The northern goshawk in Pennsylvania: habitat use, survey protocols, and status (Final Report). Pennsylvania State Univ., University Park: School For. Resour.] Although median densities was similar, populations are overall much denser in Europe than in North America. Per the IUCN, the global population of American and Eurasian goshawk is estimated to consist of 1 million to nearly 2.5 million birds, making this one of the most numerous species complex in its diverse family (the red-tailed hawk and black kite both may have a similar global population size, whereas the Eurasian sparrowhawk and common buzzard are possibly slightly more numerous than goshawks despite their smaller ranges).[Sauer, J., Niven, D., Hines, J., Ziolkowski Jr, D., Pardieck, K. L., Fallon, J. E., & Link, W. (2017). The North American breeding bird survey, results and analysis 1966-2015. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.]
Based on studies from Gotland, Finland and the southwestern United States, annual mortality for adults is 15–21%, however, feather results indicate that annual mortality for adult Eurasian goshawks is up to 7% higher in Europe than American goshawks in North America.[Hoglund, N. H. 1964. "The hawk Accipiter gentilis Linne in Fennos Kandia" (English translation). Viltrevy no. 2:195–269.][Bijlsma, R. G. (1993). Ecologische atlas van de Nederlandse roofvogels. Haarlem, Schuyt & Co.][Haukioja, E. & Haukioja, H. (1970). "Mortality rates of Finnish and Swedish goshawks (Accipiter gentilis)". Finnish Game Research, no. 31:13–20.] In many parts of the range, historic populations decreased regionally due to human persecution (especially shooting), disturbance and epidemic loss of habitat, especially during the 19th century and early 20th.[ Some states, like Pennsylvania, paid $5 bounties on Goshawks in the 1930s.]
In the 1950s–1960s declines were increasingly linked with pesticide pollution. However, in early 1970s pesticide levels in the United States for goshawks were low. Eggshell thinning has not been a problem for most populations, although California eggshells (weight and thickness index) pre-1947 (pre-DDT) to 1947—1964 (DDT in use) declined some 8-12%. In Illinois, migratory goshawks during the winter of 1972-1973 invasion year contained less organochlorine and PCB residues than did other raptors, however, these birds were probably from nonagricultural, northern forests.[Anderson, D. W. and J. J. Hickey. 1972. "Eggshell changes in certain North American birds". In Proceedings of the XVth International Ornitholological Congress, edited by H. H. Voous, 514-540. Leiden: P. J. Brill.]
Seemingly the remaining persistent conservation threat to goshawks, given their seeming overall resilience (at the species level) to both persecution and pesticides, is deforestation. Timber harvests are known to destroy many nests and adversely regional populations.[Kenward, R. E. (1996). Goshawk Adaptation to Deforestation: Does Europe Differ From North. Raptors in Human Landscapes: Adaptation to Built and Cultivated Environments, 233.][Reynolds, R. T. (1989). Accipiters. Paper read at Proceedings of the Western Raptor Management Symposium and Workshop.][Speiser, R., & Bosakowski, T. (1987). "Nest site selection by northern goshawks in northern New Jersey and southeastern New York". Condor, 387-394.] Similarly, studies from the American southwest and Canada have indicated that heavily logged areas caused strong long-term regional declines for goshawks. In Arizona, it was found that even when the nests were left intact, the noisy timber harvest work often caused failure of nesting during the incubation stage, and all nesting attempts that were occurring within of active logging failed, frequently after parents abandoned the nest.[Reynolds, R. T., Graham, R. T., & Reiser, M. H. (1992). Management recommendations for the northern goshawk in the southwestern United States.]
In North America, several non-governmental conservation organizations petitioned the Department of Interior, United States Fish & Wildlife Service (1991 & 1997) to list the goshawk as "threatened" or "endangered" under the authority of the Endangered Species Act. Both petitions argued for listing primarily on the basis of historic and ongoing nesting habitat loss, specifically the loss of old-growth and mature forest stands throughout the goshawk's known range. In both instances, the U.S. Fish & Wildlife Service concluded that listing was not warranted, but state and federal natural resource agencies responded during the petition process with standardized and long-term goshawk inventory and monitoring efforts, especially throughout U.S. Forest Service lands in the Western U.S. The United States Forest Service (US Dept of Agriculture) has listed the goshawk as a "sensitive species", while it also benefits from various protections at the state level. In North America, the goshawk is federally protected under the Migratory Bird Treaty Act of 1918 by an amendment incorporating native birds of prey into the Act in 1972. The American goshawk (as subspecies of northern goshawk, currently Eurasian goshawk) is also listed in Appendix II of the Convention on International Trade in Endangered Species (CITES).
Reference
Historical material
