Cooper's Hawk

Accipiter cooperii

Order:
Accipitriformes
Family:
Accipitridae
Sections

Breeding

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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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Cooper's Hawk with nesting material.

Nest construction normally takes about two weeks to complete. Male does most of the nest building, but there is significant building by females, which will typically land without material on nest to apparently inspect construction progress; females occasionally bring in large flakes of bark during pre-incubation and early nestling stages to line nest cup.

© Brian Rusnica , Massachusetts , United States , 23 March 2018
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Cooper's Hawk in nest.

Nests in extensive forests, woodlots of 4-8 ha (142, 82, 80, 100, 98), and occasionally in isolated trees in more open areas such as golf courses and cemeteries; common backyard breeding bird in cities of all sizes.

© Ryan Claar , Colorado , United States , 13 May 2017
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Cooper's Hawk nest.

Typically built of sticks with a “cup” lined with bark flakes; occasionally rimmed with green tree sprigs, placed in a main crotch or on a horizontal limb against the trunk of a live tree, and partly concealed and shaded by the canopy

© Michael J Good , Maine , United States , 25 May 2017
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Cooper's Hawk nest with eggs.

Completed clutch of typically pale bluish eggs at a Wisconsin nest. Numerous flakes of tree-bark are typically added during the incubation stage.

© Robert Rosenfield , Wisconsin , United States , 15 May 2017
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Cooper's Hawk egg.

Eggs are pale cobalt when fresh; fades to dirty white with bluish tinge during incubation; some eggs spotted with dried blood.

© Chris Davis , Texas , United States , 20 May 2017
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Figure 9. Adult Cooper's Hawk at nest with young.

Adult Cooper’s Hawk at nest with young. Drawing by Dan Otte, from photo by J. Papp and RNR.

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Adult Cooper's Hawk with chick in nest.

Hatchlings areable to stretch neck and bob head to receive and swallow food, and to crawl to edge of nest to defecate.

© Doug Bryant , Ohio , United States , 18 June 2018
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Female Cooper's Hawk with food at nest.

Direct feeding by female only, until young about 18–21 d and able to dismember prey. Before then, female tears food into small pieces and feeds young bill to bill.

© Brent Barnes , Oklahoma , United States , 12 June 2018

Phenology

Pair Formation

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Video: Juvenile Cooper's Hawk landing, defecating, perching.

Brownish overall with crisp streaking on underparts. Note long tail with white at the tip. This video has no audio.

© Timothy Barksdale, Arizona, United States, 24 July 1997

Unknown and possibly complex given recent discovery that Cooper’s Hawks exhibit high rates of extra-pair paternity involving both territorial and especially non-territorial floaters (188, 15, 193; S. A. Sonsthagen, A. C. Stewart, T. G. Driscoll, and W. E. Stout, personal communications). Aerial courtship display of ‘night-hawk flapping’ above tree-tops may be important in initiating courtship, signaling individual competence and territory vacancy (1; see Sounds and Vocal Behavior). Both sexes are present on nest area in early March in Wisconsin (173), and year-round presence in urban settings in Arizona (203), British Columbia (A. C. Stewart, personal communication), and New Mexico (168), with nest building and copulation by mid- to late March in New York and Wisconsin (39, 172).

In Wisconsin pairing by size is assortative: larger males tend to pair with larger females, smaller males with smaller females. Heavier individuals and heavier pairs tend to have earlier laying dates, larger broods, and more recruits than smaller individuals or pairs. However, age of breeding birds and apparent breeding site quality does not have any detectable affect on timing of breeding or annual productivity (204, 205, 206); yearling females may breed seasonally later than older females (RNR). Mass and hence size of an individual may be a heritable trait, as demonstrated by Rosenfield and Bielefeldt (204), who found that the masses of nestlings correlated positively with assumed parents (nest-attending adults), and 7 male offspring (captured as adults) were significantly and positively correlated with the mass of their putative fathers.

In Tucson, Arizona, non-random pairing by similar-aged birds: yearling–yearling, adult–adult pairings (203).

Yearling females in northeastern Oregon had lower productivity (clutch and brood counts) and used younger successional forest stands than older females (207; see Demography and Populations).

Nest-Building

Nest construction normally takes about 2 wk to complete, although this can be significantly shorter (178).

First/Only Brood per Season

First eggs usually early to late April (extremes late March to early May) in Florida (175), Arizona (208), California (183), New York (209), and Ohio (210); late April to early May (extremes mid-April to late May) in New York (39), Ontario (211), and Wisconsin (RNR, JB); early to mid-May in Oregon (212, 36; see Figure 2). Immature female breeders lay about 5–10 d later than adults (39, 36).

In British Columbia (61), dates for 38 clutches 27 April to 24 July, with 50% between 10 and 29 May; late June/July nests probably replacements. See also Bent (24).

In northern North Dakota (213), mean clutch initiation date (n = 57) over a 4-year period was 16 May (SE = 0.8 d). Most individuals returned to the study area in mid-April (a time when other northern continental populations are egg-laying), suggesting about a month between arrival and laying. Annual breeding schedule in north-central and northwestern North Dakota consistently about 2–3 weeks later than those at comparable latitudes in British Columbia and Wisconsin populations in 7-year study (1995–2001). Possible that later schedule due to phenological constraints of a shorter breeding season in this highly migratory population, which might limit ability of hawks to accumulate energetic reserves for egg production (186).

Pairs often re-nest if initial clutch lost in early incubation or before; late laying dates may involve such birds. Two-week delay in laying in Arizona-New Mexico attributed to drought and shortage of prey (162, 208).

Significant shift of about 4–5 days (from around 9 June to 5 June) to an earlier timing of egg-hatching (egg-laying) in spring across 36 years (1980–2015) for a partially migratory population in Wisconsin; shift probably a response to earlier spring (and earlier arrival of songbird prey) due to recent climate change or warming (15; see Diet and Foraging).

Second Brood per Season

No records of more than one brood.

Nest Site

Selection Process

Meng (39) reported that male selects nest site but provided no evidence. Moore and Henny (207) assumed that the female (in Oregon) selects the nest site.

Microclimate

No specific data. In northern New Jersey and southeastern New York, most nests were in mixed forest, and in more mature trees (average basal area of 30.9 m2/ha), with greater canopy cover (average 89.9%) than locally available. Canopy cover appears to be important for nesting Cooper's Hawks, possibly because it affords breeding pairs greater protection from extreme weather and predation. Understory cover does not appear to be an important feature in microhabitat nest site selection (8).

South-facing slopes were avoided by nesting Cooper's Hawks in two studies, either because increased solar radiation on such slopes reduces soil moisture, tree densities, and shading (97), or because the more deciduous nature of these slopes makes them less appealing to the hawks (8).

Site Characteristics

Nests in extensive forests, woodlots of 4–8 ha (214, 100, 97, 123, 121), and occasionally in isolated trees in more open areas such as golf courses and cemeteries (215, 183, 1, RNR, JB); common backyard breeding bird in cities of all sizes (1). A single record of a nest in dense shrub in North Dakota, where at least 2 chicks fledged (216). Pine plantations are important, possibly preferred, nesting habitat for breeders throughout the midwestern United States, with some of highest recorded breeding densities in such habitat in southeastern Wisconsin (1, 181, 121).

Nests in many species of trees, evergreen or deciduous. In Massachusetts, 27 of 48 nests (58%) in white pine (Pinus strobus; 24); in New York, 14 of 36 (39%) in American beech (Fagus grandifolia; 39); in Maryland, 4 of 6 in oaks (Quercus spp.); in Wisconsin 29 of 82 (35%) in white pine (84); in Iowa, 23 of 33 nests (70%) in oaks (217); in Missouri, 22 of 43 nests (51%) in shortleaf pine (Pinus echinata; 121); in California, 75 of 77 nests (97%) in oaks (183); in northwestern and eastern Oregon, 17 of 18 (94%) nests in douglas-fir (Pseudotsuga menziesii), and 8 of 15 (53%) in ponderosa pine (Pinus ponderosa), respectively (97); 62 of 77 nests (81%) were in laurel oaks (Quercus laurifolia) in northern Florida (46), mostly douglas-fir in northeastern Oregon (123) and ponderosa pine in New Mexico (98, 218). In Pennsylvania 14 of 18 (78%) nests in white pine (3) and in northern New Jersey, southeastern New York, 4 of 21 (19%) in white pine (previously unreported nest tree species included scotch pine (Pinus sylvestris, n = 2) and Norway spruce (Picea abies, n = 1) (219). In southern Illinois, 13 of 16 (81%) nests in shortleaf pine (220) in Tucson, Arizona, 34 of 48 (70.8%) in non-native Eucalyptus spp. (110). In San Francisco, California, one pair nested in a non-native Eucalyptus (134). In British Columbia (61), 63% of 62 nests in coniferous trees (7 species); remainder in deciduous (10 species); 3 species of trees accounted for 52% of nest sites: douglas-fir (34%), birches (Betula; 10%), and black cottonwood (Populus trichocarpa; 8%).

Bosakowski et al. (219) found that pairs in eastern North America generally use larger nest trees than pairs in western North America, possibly because eastern races are larger (by 23%) than their western counterparts.

Average height of nests 8–15 m; diameter-at-breast-height (DBH) of nest trees 21–52 cm; average percent canopy closure 64–95%; and average tree densities 243–1,159/ha (96, 97, 123, 183, 98, 121, 218); 55% canopy closure for 20 nests in Little Missouri National Grassland, western North Dakota (221). Nest site often within 1 km of water (222, 208, 96, 97), but proximity of water not necessary for successful nesting (120, 221). Nest site selection is apparently a function of: (1) proximity to hunting areas with dense prey populations; (2) availability of prey in nearby area during the fledgling dependency period; (3) historic nesting success; and (4) the gross vegetative structure of the site (98). Excluding the latter point, these listed factors are undocumented and need study range-wide; competence of individual territorial breeders is likely important, but unstudied (223).

In Oregon, yearling females nested more frequently in younger successional stages or thinned stands than adult females did (207).

In north-central Dakota, where woodlands are structurally different from those in other studied regions (including New Jersey, Maryland, Wisconsin, Oregon, New Mexico, Arizona, Utah and Arkansas), Cooper's Hawks selected nest sites with less canopy cover than average and with shorter nest trees of lesser DBH. Individuals still placed their nests at about two-thirds the height of the tree, even though they used shorter trees. In keeping with the results of other studies, nest sites were typically in flat or near flat areas with the greatest density of trees (12), but average of 13% slope in coulee nest sites of Little Missouri National Grassland of western North Dakota (221).

Overall, Cooper's Hawks exploit a wide range of nesting habitats, including those formed by radical human-induced land-use changes (such as urban areas, alien trees and plantations), probably a key factor in making this species the most abundant breeding accipiter across America's woodland and urban habitats (12).

Nest

Construction

Male does most nest building (70% in Wisconsin), but significant building by females and they will typically land without material on nest to apparently inspect construction progress; females occasionally bring in large flakes of bark during pre-incubation and early nestling stages to line nest cup. Male gathers most nest material within 100–200 m of the nest. Nest visits by male are brief, typically < 1 minute. When the nest is near-completion, female may use it as a feeding platform (1, 178, 172).

Structure and Composition Matter

Typically built of sticks with a “cup” lined with bark flakes; occasionally rimmed with green tree sprigs, placed in a main crotch or on a horizontal limb against the trunk of a live tree, and partly concealed and shaded by the canopy (39, 101, 1, 96, 123, 121, 8). Majority of 385 nests in Wisconsin built atop pre-existing bases such as squirrel or other hawk nests or detritus in tree fork (RNR, JB). Number of support branches per nest averaged 4.2 (range 2–6) (8). In Oregon, may be incorporated in masses of mistletoe (Arceuthobium spp.; 97, 123). One nest apparently built on a tree nest of an eastern woodrat (Neotoma floridana; 165). Young females use mistletoe as nest structure significantly less often than adult females do (207).

Dimensions

Nests are more broad and flat in conifers (diameter 64–76 cm; height 15–20 cm), and higher in deciduous trees (diameter ~61 cm; height ~43 cm); nest cup diameter ~19 cm; nests cup depth ~10–25 cm (39, 1).

Microclimate

No information.

Maintenance or Reuse of Nests; Alternative Nests

Individuals typically build a new nest in the same area each spring, but occasionally use the same nest in successive or intermittent years (39, 170, 224, 212, 123, RNR, JB). In Florida, 21% reuse of previous year’s nest (46). In Wisconsin, 40–60% of nests each year are built on pre-existing base (usually Cooper’s Hawk or squirrel nest, 1). In Michigan and Wisconsin, often build > 1 nest (maximum of 4 nests in Wisconsin; 1) in 4 weeks prior to incubation; distances between initial and alternative nests averaged 170 m, maximum 335 m in Wisconsin (172, 166; 172).

Adult male in Wisconsin built on alternative nest (immediate previous year’s nest) while also raising 4 young 230 m at another nest; resumed building on alternative nest in the subsequent spring (225). Unusual timing of alternative nest building may be due to high urban food levels which provided surplus energy reserves for male to prepare nest for future use; he fledged 4 young at both nests. Nest building can occur in fall in Albuquerque, New Mexico, but at unknown population frequency (B. Millsap, personal communication). Boal (226) reported nest building by ‘pairs’ of Cooper’s Hawks during ‘nonbreeding season’ in Tucson, Arizona, but gave no details.

Eggs

Shape

Elliptical to sub-elliptical (28).

Size

California: 47.50 mm (range 44.71–51.27) × 37.57 mm (range 34.89–39.43) (n = 90 eggs, 20 clutches; Western Foundation Vertebrate Zoology).

Eastern United States: 48.61 mm (range 46.74–51.67) × 38.65 mm (range 37.43–39.57) (n = 82 eggs, 20 clutches; Western Foundation Vertebrate Zoology).

Mass

Ranges from 36–52 g, and averages 43 g, decreasing to about 34 g, prior to hatching (178).

Color

Pale cobalt when fresh; fades to dirty white with bluish tinge during incubation; some eggs spotted with dried blood (28).

Surface Texture

Eggshell is smooth (178).

Eggshell Thickness

Eggshell thickness pre-DDT (i.e., pre-1947) averaged 0.367 mm (227). See Conservation and Management: Pesticides and Other Contaminants.

Clutch Size

See Demography and Populations: Measure of Breeding Activity; also see Appendix 1.

Egg Laying

Eggs are usually laid in the morning at 2 d interval (occasionally 3 d; 39).

Incubation

Onset of Broodiness and Incubation in Relation to Laying

Usually begins after third egg laid (39), occasionally with subsequent egg(s) (183).

Incubation Patch

One, in female only.

Incubation Period

Incubation period ranges from 30–36 d, though 34–36 is more typical (178).

Parental Behavior

Most diurnal incubation and all nocturnal incubation is by female. Male may incubate 10–25 min, 2–3 times daily, arriving at nest only after female leaves to accept and consume delivered prey at nearby transfer perch; departs nest immediately as female returns (39, RNR, JB). Attendance is constant except when female leaves nest briefly (2–25 min) for prey deliveries, vocal exchanges with male at dawn, defecation, and chases of predators, or when female stands to preen on nest. One female incubated 84% of daylight hours (39).

Hardiness of Eggs Against Temperature Stress

No information.

Hatching

Female typically begins incubation after the first 3 eggs are laid. Thus, with same duration of incubation for each egg (34 d), the first 3 eggs hatch on the same day; the 4th and 5th eggs laid usually hatch 1 day later, occasionally up to 3 days later. This asynchronous hatching results in later young being noticeably smaller than their older siblings (1). Hatching takes ~2 days from pipping to emergence. Shells are removed by parent(s) and dropped nearby. No information on diel pattern of hatching or adult vocalizations.

Young Birds

From Meng (39), Meng and Rosenfield (178), and Palmer (28) for eastern populations. See Figure 9.

Condition at Hatching

Altricial and nidicolous. Mass about 28 g, total length about 9 cm. Completely covered with white natal down. Eyes, blue-gray; cere and upper mandible pale pinkish tan; lower mandible pale gray-tan, darker distally; tarsi, feet, and talons nearly white. Egg tooth retained for about 10 d. Able to stretch neck and bob head to receive and swallow food, and to crawl to edge of nest to defecate. Cheep calls given at hatching.

Growth and Development

Mass Increase. Growth slow for about 3 d, then rapid until about 23 d (males, about 310 g) or 28 d (females, about 475 g); increasing divergence between sexes after 7 d. Before fledging, both sexes lose about 10% of peak nestling mass, then slowly regain by 50 d. A captive male chick from California grew rapidly for 19–20 d, reaching a mass of 240 g (165).

Growth of Body Parts. Growth rapid until 10–12 d for culmen, 20–23 d for tarsi, sexes again divergent in these respects by 7 d. Recognizably different in tarsal width by about 12 d (1, RNR).

Molt into Juvenile Plumage. By 9 d, elongating down of some regions is deep and fluffy, white to very pale yellowish-buff; new down obscures natal down in other areas. Downs pushed out by Juvenile feathers, sheaths beginning to break about 11 d and rectrices, scapulars, and remiges protruding from down by 21 d, when cere and legs lemon yellow, talons black, egg tooth (prominent until 10 d) gone. Juvenile feathering nearly complete by 28 d, although rectrices and remiges do not reach full length until 51–54 d.

Control of Body Temperature. No measurements. Probably achieved about 14 d, when diurnal brooding (except in rain) usually stops (RNR and JB).

Behavior and Locomotion. Stand feebly and flap wings by 10 d, stretch legs, “yawn,” and show awareness of small moving objects nearby by 13 d. Preen well, develop threat posture, dismember prey, flap wings vigorously by 16–18 d. Shield food from siblings with extended wings, strike at objects with feet by 24 d, when more rapid locomotor development of males apparent. Climb, jump, and flap awkwardly to nearby branches by 26 (male) to 29 (female) d. May attempt to seize food from siblings, or pull feathers and peck at heads (162), but siblicide undocumented. Nestlings dead from other causes may be eaten by siblings (178).

Causes of Death

Predation, especially by raccoons (e.g., 224) and Great Horned Owls (84, 137), probably most widespread and important cause, but largely unquantified. Nestling death or nest destruction by exposure (178), windstorm, or logging (212, 120), and starvation of youngest, smallest sibling (183, RNR, JB) also known or assumed. Disturbance by humans and/or researchers, unless prolonged (> 30 min), unlikely to bring desertion of eggs or young (120, 186, 1, RNR, JB; see also Demography: Disease and Body Parasites and Causes of Mortality). Higher mortality rates reported in adult male Cooper’s Hawks with heavier (10 g; 3.4% of body mass) versus lighter transmitters (6.5 g; 2.3% of body mass) in Florida (46). Falconers take small numbers of nestlings (183).

Parental Care

Brooding

By female only. Begins immediately after hatching, ends when young about 14 d old or during rain for a few days thereafter; female also stands or crouches with outspread wings to shelter or shade young from rain or direct sunlight (39, RNR; J. Papp, personal communication).

Feeding

From Meng (39), RNR, and J. Papp (personal communication). Direct feeding by female only, until young about 18–21 d and able to dismember prey. Before then, female tears food into small pieces and feeds young bill to bill. When female present near nest (consistently through first 12–14 d, less and less regularly later as she begins to hunt), male delivers prey to her at nearby perch and she brings food to nest. If female absent, male delivers to nest but does not feed young. For nestling diet, see Bielefeldt et al. (49) and citations therein.

Rate of feeding (one item per trip) varies with brood size (162, 228); with nestling stage, peaking in fourth week (160, 228, 106); and probably with size and abundance of potential prey (160, 229). Mean rates for entire nestling stage in broods of 3–5 are 6–9 items/d.

Nest Sanitation

Even when small, young defecate over rim of nest; adults remove uneaten food, skeletal remains, and nestling pellets (178). Adults and larvae of dermestid beetles present in all nests in New York (39).

Parental Carrying of Young

Not known to occur.

Cooperative Breeding

Not known to occur.

Brood Parasitism

Not known to occur.

Fledgling Stage

Departure from the Nest

Fledging ages geographically variable. In New York, able to leave nest at about 30 d (males) to 34 d (females), although able to clamber short distance in nest tree 4–5 d earlier (178). Wisconsin young first leave the nest (males typically about 2-4 d before females) using climbing, jumping, and flapping approximately 25 d after hatching (230, RNR). In smaller western birds, report of 27–30 d (212) may involve such short movements; average fledging age given as 31 d in Arizona (208). Fledglings return to nest for prey deliveries and roosting for at least 10 d (144, RNR).

Growth

See Young Birds. No data on growth after young leave the nest.

Association with Parents or Other Young

Parents defend young and continue to bring food—especially adult males—for up to 7 wk post-fledging, but at slight and progressively lower feeding rates (160, 66, RNR). Adults drop whole prey at nest or in trees nearby, and highly vocal fledglings fly toward parents arriving with food; able-flying post-fledglings often aggressively ‘seize’ prey from parent (39, 144, RNR). In New Mexico, > 50% of adult females deserted dependent young 2–3 wk after fledging; all deserters were in poor condition, consistent with hypothesis that fitness trade-offs associated with mate desertion can be based on costs and benefits of both current and future reproduction (66). However, it appears common for adult females, not adult males who establish territories and are more tied to territory even during non-breeding season, to leave post-fledglings before their independence (46, RNR). Young remain together (within 4 m of each other in Wisconsin; 144, 180), and near nest for 5–6 wk (165, 175) or more; one found near nest 53 d post-fledging (212). Post-fledglings in Wisconsin follow each other (movements are non-independent of siblings), ‘prone’ (laying) in groups on the ground (180), group hunt (up to 4 siblings in a group), mimic hunting behavior of adults, and rarely share food; such social behaviors of post-fledglings may be common throughout range (39, 231, 114, 1, 144, 105), but more data needed.

Ability to Get Around, Feed, and Care for Self

Little information. Initial flights awkward; fly well and range 150–300 m from nest by 3–4 wk. Apparent and successful attempts to capture insects or other prey in open grassy areas, including city lawns (175, 165, 144, JB) likely early practice in prey capture by post-fledglings. Nicewander and Rosenfield (144) reported groups of fledglings successful in 10 (56%) of 18 total hunting attacks in suburban lawn in central Wisconsin; see Diet and Foraging).

Immature Stage

Little information rangewide. Survival of 34 radio-tagged fledglings was 67% though 180 days of age in Tucson, Arizona (232), and annual survival rates for radio-tagged females in Albuquerque, New Mexico ranged from 27% to 38%; and resident urban birds (who invariably breed in their second summer of life) on average began nesting about 12 days earlier than those birds that migrated (46). Average winter home range sizes of 40 radio-tagged birds (22 males, 18 females) during natal dispersal in Tucson averaged 771 ha and did not differ between males (804 ha) and females (731 ha); these ranges included between one and three territories frequently used by other Cooper's Hawks (233). See Demography and Populations: Age at First Breeding.

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