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Photo by Jim Parrish
Photo Copyright Jim Parrish
Cooper's Hawk
Accipiter cooperii
NatureServe conservation status
Global (G-rank): G5
State (S-rank): S4B,S3S4N
External links
General information
Cooper's hawk, Accipiter cooperii, breeds from southern Canada to northern Mexico, and winters from extreme southern Canada to Central America. The species is fairly common statewide in Utah (in appropriate habitat) throughout the year. Cooper's hawk prefers woodland areas and riparian zones. Though populations of this hawk were once declining, they have recently stabilized, and are even increasing in some areas.
Breeding occurs in the spring. The male builds the nest in a tree, usually about 18 to 60 feet above the ground, and guards the nesting area from other birds. The female lays and incubates a single clutch of four or five eggs. During incubation and after the eggs have hatched, the male brings food to nest. The young can fly at about one month of age, but they are still dependent on their parents for food until they are about two months old.
Cooper's hawk eats primarily other birds, such as quail and starlings, but small mammals, reptiles, and amphibians are also consumed.
Species range
BREEDING: southern British Columbia across southern Canada to central Saskatchewan, southern Quebec, and the Maritime Provinces, south to Baja California, northern Mexico (Chihuahua, Nuevo Leon), and southeastern U.S., though basically absent from the western Great Plains (AOU 1983, Rosenfield and Bielefeldt 1993). NON-BREEDING: Washington, Rocky Mountain states, southern Minnesota, southern Ontario, and New England south to Middle America (commonly to Honduras, rarely but regularly to Costa Rica, casually to Colombia) (AOU 1983, Stiles and Skutch 1989, Johnsgard 1990, Rosenfield and Bielefeldt 1993).
Migration
Northernmost populations migratory (move north mostly March-April, southward late August-early November) but regularly present throughout most of breeding range in winter. Migrates singly or in twos or threes (National Geographic Society 1983). See Palmer (1988) for more information.
Habitat
BREEDING: Primarily mature forest, either broadleaf or coniferous, mostly the former; also open woodland and forest edge (AOU 1983, Rosenfield and Bielefeldt 1993). Nests in both pine and hardwood groves, and riparian cottonwoods and sycamores in the West; Douglas-fir in northeastern Oregon. Usually builds new nest on horizontal limb near trunk or in crotch, 6-18 meters above ground; may modify old one or squirrel or crow nest. Campbell et al. (1990) reported one instance of a nest being reused for six consecutive years in British Columbia. Rosenfield and Bielefeldt (1992) found that nesting areas were irregularly reused by the same or different adults in subsequent years.In Nevada, Cooper's Hawks were frequently sighted in montane forests and pinyon-juniper woodlands, but riparian habitat was recorded as well (Floyd et al. 2007). In California, this species is seldom found in areas without dense tree stands, or patchy woodland habitat. It nests in deciduous trees in crotches 3-23 m (10-80 ft), but usually 6-15 m (20-50 ft), above the ground. It also nests in conifers on horizontal branches, in the main crotch, often just below the lowest live limbs. They usually nest in second-growth conifer stands, or in deciduous riparian areas, usually near streams. They frequent landscapes where wooded areas occur in patches and groves (Beebe 1974) and often use patchy woodlands and edges with snags for perching (CDFG 2011). Cooper's Hawks tend to use older, taller, and less dense woodlots than Sharp-shinned Hawks in California (Rosenfield and Bielefeldt 1993). In southern California, Cooper's Hawk generally favors extensive riparian bottomlands (Garrett and Dunn 1981). In Oregon, nests were in stands of conifers that included older and taller trees, a deeper crown, and a more open understory than a typical single-story Sharp-shinned Hawk nest stand (Reynolds et al. 1982). See also Grindrod and Walton Cooper's Hawk account at http://www.blm.gov/ca/pdfs/cdd_pdfs/coha.pdf.Generally is an inhabitant of deep woods, utilizing thick cover both for nesting and hunting. Openings, especially where hedgerows or windbreaks offer shelter for prey species, may also be used when foraging. Johnsgard (1990) states that Cooper's are less fussy about the forest type than sharp-shins, and are more often "associated with deciduous and mixed forests and open woodland habitats such as woodlots, riparian woodlands, semiarid woodlands of the southwest, and other areas where the woodlands tend to occur in patches and groves or as spaced trees." In the Northwest and Northeast, conifers are used for nesting (Bent 1937, Reynolds et al. 1982), but elsewhere the preference is for hardwoods (Brown and Amadon 1968). In the Northwest a preference may exist also for the cooler microclimates offered by north and east facing slopes (Reynolds et al. 1982). In that area, the Cooper's hawk is typically found in middle-aged stands, 50 - 60 years in age, whereas the sharp-shin prefers younger stands and the goshawk older ones (Reynolds et al. 1982). That difference might express competitive displacement, because in the East, where the goshawk rarely nests, the Cooper's hawk prefers mature stands (Brown and Amadon 1968). In some areas the species seems to require large tracts of forests and to avoid human contact, in others they may use small forest tracts, (e.g., British Columbia and Nevada), woodlots (e.g., Ohio) or urban/suburban areas where they seem tolerant of human activities (e.g., British Columbia, Utah, Wisconsin, Indiana) (Hennessy 1978, Herron et al. 1985, Campbell et al 1990, Peterjohn and Rice 1991, Rosenfield et al. 1991). In New Jersey-New York, nested mostly in mixed deciduous-coniferous forest with eastern hemlock the dominant coniferous species at many sites. Tended to nest in areas with relatively large basal area and more canopy cover. Nests located in live overstory trees (43% conifers), typically within the canopy, and always in dense forest but commonly near wetland openings or source of water, on level ground or lower slopes, typically several hundred meters from paved roads (but sometimes within 100 meters or less). Avoided southern exposures (Reynolds et al. 1982, Bosakowski et al. 1992). A recent study in Missouri documented numerous Cooper's Hawks nesting in young pine plantations in essentially the same habitat as sharp-shins. Also found that trees with deformed crowns were preferred (Wiggers and Kritz 1991). Rosenfield et al. (1991) report that pine plantations are important habitat for breeding Cooper's hawks throughout the Midwest, and particularly in Wisconsin. See Kennedy (1988) for details on nesting habitat in New Mexico. NON-BREEDING: Migrates mostly along ridges and coastlines (NGS 1983). Winter habitat is much the same as in the nesting season, although open woodlands and fields may be utilized to a greater extent.
Food habits
Eats medium-sized birds (e.g., starling, thrush, quail), sometimes small birds and some up to size of adult ruffed grouse, small ground-foraging mammals, occasionally reptiles (especially in southwestern U.S.) and amphibians. Their primary food is other birds; up to 90% of its diet is composed of avian prey, with mid-sized birds such as flickers and starlings being taken preferentially (Kennedy 1980). They are frequently important predators of bobwhites and were at least formerly, before the days of factory farming, raiders of domestic fowl. These food choices have led to a great deal of persecution by humans. Additional foods include small mammals, reptiles, amphibians, and insects (Bent 1937). In the southwest and west mammals and lizards can make up as much as half the food intake (Johnsgard 1990). Young birds comprise a large proportion of the food provided to nestlings. Typically hunts from inconspicuous perch, or uses a longer searching flight. Sometimes attracted to birds at feeders. Birds may not necessarily prevail in the diet (Bielefeldt et al. 1992).
Ecology
Few data on population densities exist. Craighead and Craighead (1956) found 1554 hectares per pair in 1947-1948 in Michigan. In Maryland a density estimate of 200 hectares per pair was calculated by Stewart and Robbins (1958). Rosenfield et al. (1991) compiled nesting densities from various studies. These densities ranged from a low of 5000 hectares per pair in North Dakota in 1987, to a high of 331 hectares per pair in a pine plantation in southeastern Wisconsin in 1986. Strongly territorial. Males vigorously defend an area 30 meters in diameter around the nest site although they may forage up to 3.2 kilometers away (Brown and Amadon 1968). Johnsgard (1990) reported home range sizes that ranged from 105 to 784 hectares (the latter was seasonal home range; daily home range was 231 hectares). Nests are typically spaced 2.4 - 5.6 kilometers apart (Brown and Amadon 1968, Reynolds and Wight 1978, Kennedy 1980, Campbell et al 1990) and not usually less than one kilometer apart (Palmer 1988). The smaller sharp-shinned hawk also appears to keep similar distances from Cooper's hawk nests (Brown and Amadon 1968, Reynolds and Wight 1978), indicating interspecific aggression probably related to competition for food. Winter range is larger. Michigan birds ranged over areas of 2.4 - 3.2 kilometers in diameter. Dispersal range is limited. In Wisconsin, six males dispersed 4 - 35 kilometers (mean 12 kilometers) from natal site to nesting site; one female dispersed 14 kilometers (Rosenfield and Bielefeldt 1992). Hunt by a combination of still-hunting and searching flights along woodland edges and natural routes (Johnsgard 1990). Birds following inland migration routes apparently migrate over longer distances than those following coastal routes, and tend to have longer wings and tails, creating lower "flight-surface loading." This is thought to be an adaptation to the longer flight distances, more open country, and stronger thermal updrafts encountered along the inland routes (Smith et al. 1990). Mortality appears to be quite high during the birds' first winter, approaching 78% as opposed to only 34% per year for the adults 2 to 8 years old (Henny and Wight 1972). The maximum recorded lifespan is 8 years (Henny and Wight 1972). Life history traits place it intermediate for population turnover rate between the larger goshawk and smaller sharp-shinned hawk. This may partially explain the slower recovery of Cooper's from a population crash in the 1950s-1960s compared to sharp-shinned hawks (Bednarz et al. 1990).
Reproductive characteristics
The breeding season usually begins in early April and extends through May and June (Bent 1937, Brown and Amadon 1968). The annual molt begins in late June but can occur as late as October (Bent 1937). Southward migration commences in the northern states in late August, with September being the peak month; it is essentially over by November. Northward migration occurs from late February to early April (Brown and Amadon 1968). The male does most of the nest building and occasionally some of the incubation; most of the incubation is done by the female, which seldom leaves the nest before the young have fledged (Brown and Amadon 1968). During the pre-fledging period the male provides both the female and the young with food, while both parents feed the young for up to four weeks after they leave the nest (Brown and Amadon 1968). Only one brood is raised each year. The normal clutch is four-five eggs, with clutches of three and six being rarely observed (Bent 1937). A national average has been calculated at 3.5 eggs (Bednarz et al. 1990). Replacement clutches are laid if the first set is lost, and laying can be delayed under conditions of low food availability (Bent 1937, Snyder and Wiley 1976). Hatching success data are limited, but in areas unaffected by DDT contamination the average hatching rate ranges from about 70% to 83% (Craighead and Craighead 1956, Johnsgard 1990), with some further reduction in the brood occurring after hatching. Normal fledging success rates range from 2.1 to 3.5 for pairs with successful nests (Craighead and Craighead 1956, Schriver 1969, Henny and Wight 1972, Reynolds and Wight 1978, Herron et al. 1985); roughly 80% of nests produce at least one fledgling (Henny and Wight 1972). In areas affected by DDT poisoning these figures were reported to be dramatically reduced. The young fledge one month after hatching, the males leaving the nest three-four days earlier than the larger females. They remain dependent on their parents until they are eight weeks of age and have learned to forage on their own (Brown and Amadon 1968). Only about 19% of the birds breed in their first year. Most nest by the second year and continue breeding throughout the rest of their lives.
Threats or limiting factors
Major threats are pesticide use (especially chlorinated hydrocarbons used in Central America) and loss of habitat. Sometimes shot by hunters and farmers, or nests are robbed by falconers. PESTICIDES: The principal cause for the population crash since the 1950s has been nesting failure due to DDT poisoning. A severe decline in the eastern portion of the range was first noted in counts of migrating populations during the 1960s (Peterson 1964, Spofford 1969, Nagy 1977). More direct evidence for the role of pesticide poisoning includes observations of drastically reduced fledging success rates (Schriver 1969), reductions in egg-shell thickness (Anderson and Hickey 1972), and a strong correlation between egg-shell thinning and residues of DDT and its metabolites found in egg tissues (Snyder et al. 1973). Fledging success rates dropped from 3.53 young per successful nest prior to 1946 to 2.67 during 1946-1967 (Pattee et al. 1985). Despite the ban on DDT that has been in effect in the U.S. since the 1970s, numbers have failed to rebound to former levels in the eastern U.S. (Robbins et al. 1986). This failure to regain their former abundance may be due to the continued use of the pesticide in Central America, where at least part of the species spends the winter. An adult was found dying of acute DDT poisoning as late as 1980 (Prouty et al. 1982). Many prey species consumed are neotropical migrants, and probably continue to be contaminated by DDT during their winters south of the United States. Illegal use of DDT in this country has also been proposed as a possible cause. It is, however, still unclear to what extent DDT or other organochloride pesticides are contributing to the slow rebound of this species. In a study of contaminants in eggs from Connecticut, Maryland, Michigan, Pennsylvania, and Wisconsin, only one egg from Connecticut contained levels of DDE, a break-down product of DDT, above the level hypothesized to cause reproductive failure. The data suggested that egg shell thinning was not a significant problem in these states in 1980, although at least two individual birds had thin-shelled eggs containing high residues. Other contaminants, including other pesticides, PCB, lead and mercury, also showed up at levels below hypothesized impact levels (Pattee et al. 1985). In addition to the hazards of long-lived, bioconcentrating organochlorine pesticides such as DDT, the more widely used and acutely toxic organophosphate pesticides may pose a threat. Two reports of poisoning were made in the 1980s (Rosenfield et al. 1991). So little effort has been put into monitoring this type of poisoning in dead raptors, that it is impossible to assess the magnitude of this threat. HABITAT LOSS: Deforestation has also been cited as a current threat and may become increasingly important. Required habitat (dense forest isolated from human activities or narrow riverine forest corridors) is under pressure for forest product harvest and development (Snyder 1978, Herron 1985, Weir 1987). Habitat loss was cited as the primary threat to raptor populations in a recent survey of U.S. state agencies by the National Wildlife Federation (Rosenfield et al. 1991). Rosenfield et al. (1991), however, concluded that breeding habitat does not appear to be limiting for this species in Wisconsin. They found that hawks often utilized pine plantations for nesting, and in fact may achieve their highest nesting densities in such habitat. Similarly, Wiggers and Kritz (1991) found hawks nesting in rather small stands (an average of 4.1 hectares) of young pines. If this habitat use is common in Wisconsin, it is probably also the case for neighboring Minnesota and Michigan, and suggests that habitat may not be limiting in the Great Lakes region. Also, reports that this species has been moving in to urban/suburban areas also raise questions about the importance of habitat loss (A. Stewart, pers. comm.). Other threats include continued persecution by hunters or irate farmers, and the collection of live birds by falconers. Although bounty hunting was once a major mortality factor for this species, that threat has been curtailed by the legal protection now given all birds of prey. Apart from humans, the greatest enemies are probably other raptors. Great horned owls (BUBO VIRGINIANUS) are known predators (Terres 1980). Goshawks (ACCIPITER GENTILIS) are competitors (Reynolds et al. 1982). Nestlings and eggs are also preyed upon by raccoons (PROCYON LOTOR), crows (CORVUS spp.), and possibly snakes (Schriver 1969, Campbell et al 1990).
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
