Cooper's Hawk

Accipiter cooperii

Order:
Accipitriformes
Family:
Accipitridae
Sections

Distribution, Migration, and Habitat

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Figure 1. Distribution of the Cooper's Hawk.

Black dots represent new southern nest records. See text for details.

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eBird range map for Cooper's Hawk

Generated from eBird observations (Year-Round, 1900-present)

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Figure 2. Cooper's Hawk annual cycle.

Annual cycle of breeding, migration, and molt in the Cooper’s Hawk. See text for details of timing at specific locales. Thick lines show peak activity, thin line off peak.

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Figure 4. Relative abundance of Cooper's Hawk during the breeding season.

Based on data from the North American Breeding Bird Survey, 2011–2015. See Sauer et al. (2017) for details.

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Figure 5. Timing of autumn migration.

Timing of autumn migration of Cooper’s Hawks at four major migration watchsites across North America, based on observations between 15 August and 15 December. Data are presented as five-day running means of the percentages of the total annual count for each day.

Distribution in the Americas

Breeding Range

Breeds throughout coterminous United States, also southern Canada and scattered throughout Mexico; primarily breeds south of boreal forest in deciduous or mixed-deciduous forest regions (Figure 1; see also eBird range map and Figure 4). During perhaps the past 15 years, range and numbers have expanded greatly in many regions, particularly urban areas (see Historical Changes), but also farther north in Canada (2) and into south-central Mexico (4). In Canada, breeds from central British Columbia and Alberta through southern Manitoba, southern Ontario, to southern Quebec, and potentially southern New Brunswick (59, 60, 61; see eBird range map). In Mexico, uncommon to fairly common resident breeder in highlands (1,000–3,000 m) of north-central Baja peninsula and, on mainland interior, northern Chihuahua south to Oaxaca, and possibly Veracruz (62, 63; see eBird range map).

Overwintering Range

Same as breeding range except that birds from approximately the northern third of the species' breeding range are migratory, generally heading south in autumn (28, 64) or partially migratory (RNR, JB); some southwestern breeders also known to migrate (65, 66, 67, 64), and some individuals in southern California appeared to migrate up to 993 km north. Some individuals overwinter close to their breeding sites (68, 67). Most birds overwinter within conterminous United States, plus most of Mexico (Figure 1; 62), south to Costa Rica (uncommon, 69), and possibly Panama (70), perhaps Colombia (55) and Cuba (71). Ecological factors affecting differences among the breeding ranges of Cooper's Hawk and its North American congeners (Sharp-shined Hawk [Accipiter striatus], Northern Goshawk [A. gentilis]) are uncertain.

Distribution Outside the Americas

Four adult Cooper’s Hawks were recorded during fall migration in 2007 at Cabo de San Antonio, the westernmost tip of Cuba (71).

Nature of Migration

Typically migrates singly, but occasionally occurs in groups of 2–5 individuals, following mountain ridges and coastlines. Flight generally involves both soaring and flap-sailing (72).

Individuals from northern third of breeding range allegedly more migratory than those farther south (28, 73). Millsap (74) found the potential for a temporal advantage to residency for female birds in securing a nesting territory. However, not all breeders in the southwestern United States are resident; e.g., in New Mexico, 99% of urban females were resident, whereas 93% of exurban females migrated (74). Based on band recoveries, no apparent difference in migratory tendency between urban and rural birds in Wisconsin where longest migratory movements into southern United States, Mexico, and Central America were of urban birds (75, RNR). In Victoria, British Columbia, breeding adults are non-migratory, whereas juveniles are migratory (76). In California and Arizona, some birds from nests south of 35°N demonstrate not only migratory behavior but northward migration (64).

Timing and Routes of Migration

See Figure 2. Data on Cooper's Hawk migration is primarily collected at autumn watchsites throughout the country and from band returns to the U.S. Geological Survey Bird Banding Laboratory. Breeders from eastern North America overwinter mostly in central and southern United States (77, 78); those in the West sometimes overwinter in central and southern Mexico (45; B. Millsap, unpublished data) and those in Rocky Mountain and Intermountain regions overwinter along the Pacific Coast of Mexico (from Sinaloa to Jalisco) (79).

Fall

See Figure 5. Autumn movement from late August to early November, with peak flights generally late September to mid-October (Cape May Bird Observatory, Hawk Mountain Sanctuary, unpublished data). Most yearlings migrate about 1 wk earlier than adults, and females precede males in both age categories by several days, but there is considerable temporal overlap of these groups (78, 80, 81, 82). Study of timing of migration in Wisconsin (83) found that second-year Cooper's Hawks (age 1–2 yr old) migrated later than yearlings and that after-second-year birds (> 2 yr old) migrated later than second-year birds. Yearling males migrated later than yearling females, but second-year and after-second-year females migrated later than males. In coastal California between 1983 - 2005, Hull et al. (82) found that hatch year (HY) females migrated before HY males, after hatch-year (AHY) females migrated before AHY males, HY females migrated before AHY females, and HY males migrated before AHY males.

Routes in Fall

In the East, fall migrants concentrate along shorelines of the Great Lakes and along Appalachian ridges, and also funnel down such peninsulas as Cape May, New Jersey, and Florida; in the eastern United States, coastal flights tend to be much larger than inland flights (Table 1). From Hawk Cliff, Ontario, birds migrate westward along the northern shore of Lake Erie and then disperse southward (78); birds moving west of Great Lakes spread southward. Birds from interior Canada may first head southeast (toward Wisconsin) to avoid crossing the Great Plains (43). Most birds from Rocky Mountains and farther west head directly south (84, 45, 64), though some may migrate northward (64).

Spring

Most migration occurs March through May (39, 43; 67). Males precede females and adults precede yearlings (39), the opposite of the autumn pattern. Duncan (78) speculated that the autumnal pattern, which is similar to that of the Sharp-shinned Hawk (85), occurs because inexperienced immatures must track the migration of their departing avian prey. Migratory adult males in spring may be under more pressure to migrate early, because of competition for territories on breeding grounds.

Sullivan et al. (86) documented a shift to earlier spring migration in the Great Lakes region, consistent with climate change on a continental scale. This is supported by the findings of a gradual shift to earlier nesting phenology across 36 years in Wisconsin by Rosenfield et al (15).

Migratory Behavior

The species regularly hunts on migration. In fact, recent information suggests that a relatively small proportion of a migrating individual's day is spent actually migrating. Ten radio-tagged migrating individuals (6 adults, 4 immatures) spent, on average, 57% of total daylight hours perched, 28% hunting, and only 12% migrating (87). Lynn et al. (88) documented some use of wildlife water catchments in the fall, suggesting that, at least in arid regions, the species may seek artificial sources of water on migration.

As with many birds of prey, major autumn flights typically occur on days of northwest winds with clear to partly cloudy skies, which usually follow the recent passage of a low-pressure front (89). These winds, blowing perpendicular to the Appalachian ridges, are forced upward, resulting in a rising air mass at the top, along which the hawks can glide (39). Counts of Cooper's Hawks at Hawk Mountain Sanctuary, Pennsylvania, were highest on the day of and the day after a cold front, and then declined by an average of 27% over the following 3 days (90). Species is said to be reluctant to cross water (91, 92) and individuals are not likely to cross water barriers > 25 km (K. Bildstein, unpublished data). Migration is not dependent on thermals; concentrations may be observed along lakeshores and other coastlines. Flight speeds of between 34 to 88 km/h (mean 47 km/h) were recorded for 12 individuals migrating over Hawk Mountain, Pennsylvania (72).

Meehan et al. (93) used stable-hydrogen isotope ratios to determine the natal latitudes of immatures migrating through the Florida Keys; found that most individuals migrating through the region were born in the Mid-Atlantic and southeastern United States, that males and females came from similar latitudinal origins, and that the average date of passage for northern and southern Cooper's Hawks did not differ.

Control and Physiology of Migration

Fat stores in Cooper's Hawks migrating through central New Mexico averaged 3–12% of total body mass, but varied across season, age and sex. On average, body fat was higher in spring than in autumn (although equivalent differences were not detected in adult males), higher for adults than immatures, and higher in females than in males (94).

Among accipiters captured at the Idaho Bird Observatory from late August through October, mean baseline corticosterone levels were significantly higher in Cooper’s Hawks (95). Baseline corticosterone level was marginally higher in fat Cooper's Hawks than in lean individuals (95). Only Cooper’s Hawks showed a sex difference in baseline corticosterone levels, with after-hatch-year males having significantly higher levels than after-hatch-year females (95).

Habitat in Breeding Range

Deciduous, mixed, and coniferous forests (24, 96, 97, 98, 99, 67), and deciduous stands of riparian habitat (100, 98, 74). Tolerant of human disturbance and habitat fragmentation (101, 102, 99, 103, 104, 74). Increasingly in recent years, breeds in suburban and urban areas (101, 105, 106, 99, 5, 107, 3, 108, 104, 67). See also Breeding: Nest Site.

Although previously believed to avoid urban landscapes, Cooper's Hawks have recently proven remarkably adaptable to such areas. Affinity for human-altered habitats (including housing areas, plantations, and high-use recreational areas) is possibly because developed areas generally support higher numbers of favored bird prey. Also, Cooper's Hawks are adapted to hunting in structurally complex habitats, which urban/suburban environments mimic (109). Thus, not surprisingly, the species often nests at higher densities in such regions than in ‘natural' habitats; e.g., in Tucson, Arizona, most nests were in, or close to, urban areas, where nesting density was higher than in natural areas (110, 109). In Wisconsin, nesting densities in urban/suburban areas, as well as in conifer plantations, also were higher than those recorded for the species elsewhere (272 ha/breeding pair, n = 13; 111, 107). In Albuquerque, New Mexico, between 2011–2015, annual density was recorded at 1.01 occupied nesting territory per km2 and the population was growing (74).

Some authors have expressed concern about the quality of urban habitats compared with rural forest tracks (8), and have suggested that urban habitats may be acting as ecological traps for the species (see 5 and 6, who found that urban pairs in southeastern Arizona experienced greater overall failure rates in breeding attempts due to nestling mortality attributable to trichomoniasis infections). However, that disease was time-specific in effect and later research showed that urban habitat is not an ecological trap in Arizona (112), nor are cities ecological traps in Wisconsin (113, 111, 14) or New Mexico (74).

Urban sites have included isolated trees in residential neighborhoods; industrial sites, consisting of strip malls, warehouses, recreational fields, and shopping centers; and wooded city parks (105, 114, 115, JB, RNR). Forest edge habitat may be included within the home range of breeders and may serve as primary hunting sites (116, 39, 117, 8). In fact, increased edge habitat was a strong predictor of the presence of Cooper’s hawks in western Washington (118). Ward and Mannan (119) speculated that high temperatures at lower elevation cities may be beyond the tolerance of breeding Cooper’s Hawks.

Comparing nesting habitat of Cooper's Hawk, Sharp-shinned Hawk, and Northern Goshawk is difficult because of inherent differences in habitats among study sites (11). Comparisons with Sharp-shinned Hawk show clear differences in nest site use between the two species. However, comparisons with Northern Goshawk vary among studies; criteria for the two species appear to overlap in many regions. It has been suggested that body size may be a useful predictor of nest-site selection. However, in their review of the literature, Siders and Kennedy (9) found that nest tree diameter is the only parameter consistently and positively linked with body size, suggesting body size alone may not be sufficient for predicting suitable nesting habitat for American accipiters.

In Wisconsin, compared with Sharp-shinned Hawk, Cooper's Hawk tends to nest in areas with older (30 yr), taller (12 m), and fewer trees (average of 557 trees/ha); Sharp-shinned Hawks are also more nearly reliant on coniferous stands and more often use lowland conifers as nesting habitat (120, 99, 11). In mid-aged (25–49 yr-old), dense (800–1,000 trees/ha) pine plantations in Missouri, vegetative structure such as canopy cover (81–82%) and canopy height (16–18 m) at nest sites overlaps greatly for Cooper's and Sharp-shinned hawks (121). In Wisconsin, nesting sites of Cooper's and Sharp-shinned hawks differed in terms of tree height, nest tree diameter (DBH), nest height, nest height relative to tree height, canopy cover, canopy height, tall shrub density, tree density and mean DBH. Some differences can be attributed to the fact that Cooper's Hawks use stands with greater deciduous elements, whereas Sharp-shinned Hawks use conifer-dominated stands. Measures of understory canopy cover, ground cover, low shrub index, understory tree density, basal area, distance to nearest forest opening, and distance to water were similar for the two species (11).

In the New Jersey/New York region, nest stand attributes were similar for Cooper's Hawks and Northern Goshawks, except that Cooper's Hawk nest sites had more shrub cover. However, Cooper's Hawk nests were generally on flatter terrain, and closer to roads, forest openings and human habitation (8).

In conifer forests in Oregon, principal habitat differences among the 3 accipiter species were linked to the age of the nesting stand, with Sharp-shinned Hawks in the youngest (25–50 yr-old) and densest (1,180 trees/ha) forest stands, Cooper's Hawks in intermediate stands (30–70 yr-old, 907 trees/ha), and Northern Goshawks in older (150 yr) and more open stands (482 trees/ha) (122). Moore and Henny (123) reported comparable results for nest sites of these species, also conifer forests in Oregon, and noted that vegetative structure at Cooper's Hawk nests was similar to that described in eastern deciduous forests (96).

See also Breeding: Nest Site and Diet and Foraging: Microhabitat for Foraging.

Habitat in Migration

Few data. Migrating individuals along the Kittatinny Ridge, Appalachian Mountains, Pennsylvania generally showed a preference for deciduous forest cover versus open or human-occupied areas, although immatures made more use of open habitats than adults did. These data suggested that natural forests along these flyways are important for migrating accipiters (87).

Habitat in the Overwintering Range

Few quantitative data. In Arizona occupies same plant communities used in summer (65). In central and southeastern Texas, overwintering (November–March) individuals inhabit canal banks and agricultural fields, commonly perch on fence posts and live oaks (Quercus sp.; D. Gawlick, personal communication). While one study found Cooper’s Hawks to be frequent avian predators at winter bird feeders (124), another study (125) found that use of bird feeders was not statistically different from a model based on random visits to feeders.

In southwestern Tennessee (126), 5 individuals with radio transmitters were followed November–March in 2 different years; diurnal winter habitats used by these birds were ranked from most to least preferred: forest ≥ edge ≥ field ≥ other. This pattern differed significantly from habitat available—on average, individuals spent 73% of daytime in forests, although forests comprised only 47% of the available habitat. In Indiana, wintering Cooper’s Hawks in urban areas were found primarily in parks and residential areas (125).

Historical Changes to the Distribution

For historical changes in numbers, see Demography and Populations: Population Status; also Conservation and Management: Effects of Human Activity, and Table 1. Changes in numbers tend to correlate with changes in distribution (i.e., fewer birds, generally more restricted distribution); however, information specific to changes in distribution are limited.

Generally speaking, the Cooper's Hawk was a widespread species with robust numbers up to the early 1900s; it thrived in small farm/woodlot habitat of eastern North America during the 1800s (24). A decline in eastern breeding population was suspected in early 1900s, especially in settled areas, perhaps related to increased shooting pressure as firearm numbers and efficiency increased (e.g., New York; 127). Western population apparently more stable, but little information. A significant and widespread decline in numbers starting in the late 1940s, apparently related to use of pesticides; concurrent declines in annual reproductive success were noted by Henny and Wight (128).

Changes in distribution that reflect this:

1) Wisconsin (129): few breeding records during 1960s versus widespread breeding in 1980s (120);

2) southern California (130): loss of breeders in lowland riparian areas, where woodlands much reduced, especially Colorado River valley, showing habitat loss also a factor in declines;

3) New York State (131): decline in numbers and reduced breeding range;

4) Vermont (132): loss of numbers, and apparently reduced range as well, starting in 1930s; no recovery up through 1980s.

Slow but steady increase in breeding numbers and success starting in the late 1960s and early 1970s (28; see also Table 1; North American Breeding Bird Survey Trend Results). Significant population increases and range expansions starting in 1990s, most noticeable in the form of breeders colonizing urban and suburban areas. For example, first breeding record (2 nests) for New York City since 1955 recorded in 1999 (133); and rapid colonization of Long Island, New York in 1990s (see above, New York State). First breeding record for San Francisco, California in 1994 (134).

Fossil History

Recorded in late Pleistocene (< 0.5 million years before present) deposits from California, New Mexico, and Florida (135, 136: 93).

Recommended Citation

Rosenfield, R. N., K. K. Madden, J. Bielefeldt, and O. E. Curtis (2019). Cooper's Hawk (Accipiter cooperii), version 3.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.coohaw.03