Gavilán de Cooper

Identificación

Cooper's hawk is a medium-sized hawk and relatively large for an Accipiter. Compared to related species, they tend to have moderate-length wings, a long, often graduated or even wedge-shaped tail and long though moderately thick legs and toes. Their eyes tend to be set well forward in the sides of the relatively large and squarish-looking head (though the head can look somewhat rounded if the feathers on the nape are held flush) and a relatively short but robust bill. They have hooked bills that are well-adapted for tearing the flesh of prey, as is typical of raptorial birds. Generally, Cooper's hawks can be considered secretive, often perching within the canopy, but can use more open perches, especially in the western part of the range or in winter when they may use leafless or isolated trees, utility poles or exposed stumps. On perched hawks, the wing-tips tend to appear to cover less than one third of the tail, sometimes seeming to barely cover the covert feathers. As adults, they may be a solid blue-gray or brown-gray color above. Adults usually have a well-defined crown of blackish-brown feathers above a paler nape and hindneck offset against their streaked rufous cheeks. Their tail is blue-gray on top and pale underneath, barred with three black bands in a rather even pattern and ending in a rather conspicuous white tip. The adult's underside shows a bit of whitish base color overlaid heavily with coarse, irregular rufous to cinnamon bands, though these narrow into marginal shaft streaks around the throat. Against the rich color on the rest of the underside, the pure white crissum on adults is conspicuous. Adult females may average slightly more brownish or grayish above, while some adult males can range rarely into almost a powder blue color. Although little regional variation is known in the plumage, adult coloring in the Pacific Northwest averages slightly darker overall. Aberrant pale plumage was recorded in at least four total birds of both sexes, all of which were almost completely white and lacked any underside streaking. These birds had faded back color and lacking strong barring on the tail. An aberrant dark female was also recorded. As a juvenile, she had a blackish-brown (rather than mid-brown) back and dark inky feathers below with grayish ground color barely showing. Later she produced an aberrant male with similar characteristics that successfully fledged. The latter two were possible cases of melanism and such dark variations are virtually unprecedented in any Accipiter species.<p>Juveniles of the species are generally dark brown above, though the feathers are not infrequently edged with rufous to cinnamon and have a variable whitish mottling about the back, wing coverts and, mainly, the scapulars. Juvenile Cooper's tend to have streaking or washing of tawny on the cheeks, ending in a light nuchal strip, giving them a hooded appearance unlike the capped appearance of adults (some juveniles, unlike adults, may manifest a slim supercilium as well). The crown is brown on juveniles rather than blackish as in adults. The tail is similar to that of the adult but more brownish and sometimes shows an additional fourth band. The juvenile has more pale white to cream base color showing than older birds, with variable dusky throat striping and mid-brown streaks, which appear as sharply defined from about the lower throat to the lower breast. The juvenile may have brown to black spots or bars on the thighs with thin black streaks mostly ending at the belly and conspicuous white crissum and undertail coverts. Juveniles can tend to appear more "disheveled" and less compact than adults in feather composition. In flight, though usually considered medium-sized, Cooper's hawks can appear fairly small. This effect is emphasized by the short wings relative to the elongated tail (unlike unrelated hawks, the wingspan is usually less than twice as broad as the total length). The species tends to have rounded wings, a long rounded tail and long legs, much like other Accipiters. Cooper's hawks have a strong flight with stiff beats and short glides, tending to do so on quite level wings with wrist thrust forward yet the head consistently projects. The 5 outer functional primaries are notched on their inner webs, the outermost is the longest, the next outermost nearly as long. When soaring, these hawks do so on flattish or, more commonly, slightly raised wings, with fairly straight leading edges. Against the barred underbody on adults, the wings are more or less flecked in similar color, with pale greyish flight feathers and a broadly white-tipped tail correspondingly barred with dark gray. Meanwhile, the upperside of adults is essentially all blue-grey. Juvenile are mostly dark above though manifest a hooded effect on the head and a rufous-buff edges and especially whitish mottling, the latter can be fairly apparent. Juveniles are mainly whitish below with neatly dark streaks about the wing linings, breast, flanks and thighs, with bars on the axillaries and flight feathers. The tail of the juvenile has a broadly white tip and bars like adults but the ground color is a paler shade of gray.<p>Adults have eyes ranging from light orange to red, with males averaging darker in eye color, while those of juveniles are yellow. Among 370 breeding hawks from different parts of the range, 1-year-old males usually had light orange eyes and 1-year-old females usually yellow eyes. Meanwhile, males of 2 or more years old always had consistently darker eyes than the eyes of females of the same relative age, with most males of the age having largely either orange (40.4%) or dark orange (32.3%) eyes, while female eyes at this stage were light orange or lighter. From the second year, the eyes of Cooper's hawks may grow darker still but stop darkening shortly thereafter. 3-year or older males were found to have predominantly dark orange (37.3% vs 21.6% of similar age females), red (34.6% vs 3.3% of similar age females) or mid-orange (26.6% vs 55% of similar age females). For unclear reasons, far more adults in British Columbia and North Dakota (83% of males, 63% of females) had dark orange or red eyes (which also manifested at an earlier age in British Columbia) than mature hawks in Wisconsin (49% of males, 14% of females). Most females over 2 years old in Wisconsin were found to have light orange eyes. The purpose of bright eye color in the hawks may be correlated to feeding stimulation of nestling hawks (i.e. darker orange or red objects may be more perceptible and tend to be pecked at more so than duller colors). The eyes of this hawk, as in most predatory birds, face forward, enabling good depth perception for hunting and catching prey while flying at top speeds. Adults have greenish yellow ceres and have legs of orangish to yellow while these parts on juveniles are a paler hue, yellow-green to yellow. The prebasic molt begins in late April–May and takes about 4 months. The female usually begins to molt about 7–10 days sooner than the male. Molts occur inward towards the body on the wing feathers. Tail molt may generally start with the middle tail feathers, proceeding posteriorly to the upper tail coverts, also starting with the median feathers on the scapulars. Up to 36% of juvenile feathers may be retained in the second pre-basic molt. Arrested molt has been recorded in the late nesting period, often pausing after the third primary is molted. Molts tend to be halted especially when food supplies are down during the brooding stage, and may be resumed after the stress of feeding the brooding diminishes.<p>Cooper's hawks are fairly variable in size. There is usually minimal to no overlap in dimensions between the sexes, with females being considerably larger than males. On average, she may be about 20% larger linearly and around 40% heavier (though can be up to 125% more massive). More westerly Cooper's hawks (roughly west of the Rocky mountains) show slightly less pronounced sexual dimorphism than hawks of the species elsewhere. Sexual dimorphism in Cooper's hawks is most reliably measured by wing size, talon size, then body mass. Although there is some margin of error, within a given region dimensions of the two sexes never overlap in these regards (but may overlap marginally in tarsal and tail lengths). In general terms, Accipiter species are among the most sexually dimorphic in size of all raptorial birds. Sexual dimorphism in Accipiters may be due to greater male efficiency through smaller size and resulting agility in food gathering for the family group. Meanwhile, the female may be better suited to the rigors of brooding (including perhaps most nest defense) due to her larger size, also allowing the sexes to compete less on the same food sources. Geographic variation in body size has also been found, with more easterly hawks tending to be rather larger on average than those found in western North America. On the contrary, in the American southwest, the species may reportedly reach its largest sizes but there is little evidence that these birds average distinctly larger than the large bodied individuals measured in the more northeasterly parts of the species' range in North America, from eastern North Dakota to New Jersey. The size variation evidenced in Cooper's hawks is apparently the most pronounced of any of the three North American species of Accipiter. However, Cooper's hawks are one of an estimated 25% of studied bird species that do not appear to correspond to Bergmann's rule (i.e. being larger where living farther north) instead varying in size much more so by longitude. Furthermore, juveniles can differ somewhat in size, tending to be slightly lighter and smaller than older birds, but not infrequently averaging longer in tail and especially wing length. Total length of full-grown birds can vary from 35 to 46 cm (14 to 18 in) in males and 42 to 50 cm (17 to 20 in) in females. Wingspan may range from 62 to 99 cm (24 to 39 in), with an average of around 84 cm (33 in).<p>Body mass, along with standard measurements, is much more frequently measured than total length or wingspan in different populations. Museum specimens from the western United States averaged 280 g (9.9 oz) in 48 males and 473 g (1.043 lb) in 20 females, while those sourced from the eastern United States averaged 338 g (11.9 oz) in 16 males and 566 g (1.248 lb) in 31 females. Average weight of 104 male migrating hawks in Cedar Grove, Wisconsin was 342 g (12.1 oz) (with adults averaging 4% heavier than juveniles), whilst the average of 115 females migrants was 518 g (1.142 lb) (with adult averaging about 5.5% heavier than juveniles). A different sample of Wisconsin Cooper's hawks reportedly averaged 327 g (11.5 oz) in males (sample size 60) and 580.3 g (1.279 lb) in females (sample size 57). At Cape May Point, New Jersey, weights were similar as in Wisconsin (although only hatching-year juveniles were apparently weighed), with averages of 339.2 and 347 g (11.96 and 12.24 oz) in two samples of males and 518 and 530.3 g (1.142 and 1.169 lb) in the two samples for females. Migrant hawks in the Goshute Mountains of Nevada were significantly lighter than the eastern ones at 269 g (9.5 oz) in 183 first year males and 281 g (9.9 oz) in 177 older males and 399 g (14.1 oz) in 310 first year females and 439 g (15.5 oz) in 416 older females. Weights were similar to the Goshutes in the Marin Headlands, California where 50 males (all first-years) averaged 288 g (10.2 oz) and 117 first-year females averaged 417 g (14.7 oz). Averaged between early and late summer, the average mass of males in Oregon was 280.7 g (9.90 oz) and that of females was reported at 488.4 g (1.077 lb). The average weights of Cooper's hawks from Oregon was about 19.4% lower in males and 14.5% lower in females than those from Wisconsin but the Oregon hawks evidenced less seasonal variation in weight. In British Columbia, males averaged 295.8 g (10.43 oz) and females averaged 525.5 g (1.159 lb) while in western and eastern North Dakota, males averaged 301.5 and 318.7 g (10.64 and 11.24 oz) and females averaged 514.3 and 563.3 g (1.134 and 1.242 lb). In northern Florida, males averaged 288 g (10.2 oz) and females averaged 523 g (1.153 lb). In general, males may weigh anywhere from 215 to 390 g (7.6 to 13.8 oz) and females anywhere from 305.8 to 701 g (0.674 to 1.545 lb), the lightest hawks generally being juveniles recorded from the Goshutes of Nevada, the heaviest known being adults from Wisconsin.<p>Among standard measurements, the wing chord may vary from 214 to 252 mm (8.4 to 9.9 in) in males and from 247 to 278 mm (9.7 to 10.9 in) in females. Wing chord is generally commensurate with body mass, averaging largest in the heavier hawks of eastern North Dakota, where males averaged 232.6 mm (9.16 in) and females 264.3 mm (10.41 in), and in Wisconsin, where males averaged 236.9 mm (9.33 in) and females 267.1 mm (10.52 in) (those from Cape May also being similar to those two samples). However, smaller, more westerly hawks such as those in the Goshute mountains, where males measured at a mean of 224.1 mm (8.82 in) and females at a mean of 254.8 mm (10.03 in), and in British Columbia, with a male mean of 227 mm (8.9 in) and female mean of 256.8 mm (10.11 in), were proportionately longer winged relative to their other body proportions. The tail of males may vary from 166 to 211 mm (6.5 to 8.3 in) and that of females at 203 to 242 mm (8.0 to 9.5 in), consistently over 200 mm (7.9 in) in females and averaging under 190 mm (7.5 in) in males. In tarsus length, males may vary from 55.2 to 73 mm (2.17 to 2.87 in), with an average of 64.1 mm (2.52 in) in museum specimens, and females from 62 to 76 mm (2.4 to 3.0 in), with an average of 71.1 mm (2.80 in) in museum specimens. The culmen may measure from 11.7 to 17.5 mm (0.46 to 0.69 in) in males, averaging about 16 mm (0.63 in), and from 17.5 to 23 mm (0.69 to 0.91 in) in females, averaging about 19 mm (0.75 in). The hallux claw, the enlarged rear talon featured on nearly all accipitrids, may measure from 17 to 21.7 mm (0.67 to 0.85 in) in males, averaging about 19.2 mm (0.76 in), and from 19.8 to 26.7 mm (0.78 to 1.05 in) in females, averaging about 23.3 mm (0.92 in). The footpad of Cooper's hawks may measure in males 61 to 70.2 mm (2.40 to 2.76 in), averaging 66 mm (2.6 in) in 42, and in females 74.1 to 83.5 mm (2.92 to 3.29 in), averaging 76.8 mm (3.02 in) in 23. For unclear reasons, the smaller-bodied hawks found in British Columbia were found to be proportionately larger footed, median toe length between sexes of 37.3 mm (1.47 in), than the larger bodied ones in Wisconsin.<p>Some authors have claimed that during breeding Cooper's hawks may utter well over 40 call variations, which would rank them as having among the most varied collection of calls recorded for any raptor. However, many such variations are probably quite subtle (marginal differences in harshness, clarity, tempo and volume) and other authors have diagnosed only four overall call types. The typical call of a Cooper's hawk is a harsh, cackling yelp. This call may be translated as keh-keh-keh..., males tending to have a higher pitched, less raspy and faster-paced voice than females. However, some variants uttered by males were surprisingly actually deeper than the female's version of said calls. A still more modulated and raucous version is given during the dawn chorus. Some studies have indicated that pairs nesting in more deeply wooded areas may vocalize more frequently due to inferior sight lines. However, hawks nesting in urban areas of Arizona do not seem to vocalize less than their rural nesting counterparts. There is perhaps some evidence that individual hawk's voices may become lower pitched with age. When coming with food to the nest or while displaying during courtship, the male may let out a nighthawk-like kik, apparently this call is more prevalent in pairs using thicker woods. Infrequently, females may utter the kik call as well, apparently when looking for her mate or gathering nesting materials. Many soft calls have been recorded in intimate or "conversational" interactions, exclusively between breeding pairs and between mothers and their broods. The initial call of the young is a cheep or chirrp, which by the time they are fledgling young alters to a penetrating hunger call, eeeeeeee-oo or tseeeee-ar (among different transliterations). The higher pitched calls of the young may even extend to females nesting within their first year while still in immature plumage. Females have what is often thought of as their own hunger cry, whaaaa, heard especially in poorer food areas, when the male appears. Nonetheless, the females whaaaa call has also been uttered in different contexts, such as during nest building and during a "postural bowing" display, and some authors inferred that it may be a means of communicating to the male that it is not dangerous for him to approach her (as female Accipiters can be dangerous to the much smaller males). Generally, Cooper's hawks are silent outside the breeding season. Rarely, though, some males that appear to be isolated from any other hawks of their species have been known to call during winter.<p>Accipiter species in North America are arguably the most vexing raptor to identify in the continent. The other two species in North America are the smaller sharp-shinned hawk (Accipiter striatus) and the larger northern goshawk (Accipiter gentilis). Compared to the other two Accipiters, Cooper's have an intermediate amount of feathering at top of the tarsus, as well as intermediate relative middle toe length and eye proportions, but have relatively the longest tail and the shortest wings of the three. Cooper's and sharp-shinned hawk are very similar (sometimes considered almost identical) in plumage characteristics at all stages of development. Most Cooper's hawks are considerably larger than most sharp-shinned hawks. Generally, Cooper's species is crow-sized, with the males about the size of a small crow and the females the size of a large crow, while most sharp-shinned hawks are about the size of a large jay. Also in the hand, Cooper's hawks and sharp-shinned hawks may be fairly reliably distinguished by their sizes, with the smallest male Cooper's always being heavier and larger clawed than the largest female sharp-shinned hawk (with a 97–98% difference in dimensions of the wing and tail). However, in the field, especially when hawks must be identified in at a distance or at unfavorable angles (such as when migrating) or at a brief glance (such as when hunting), even experienced birdwatchers may not always be able to certainly distinguish the two species, especially female sharp-shins against the nearly similarly sized male Cooper's. The sharp-shinned hawk usually evidences a slimmer, slighter look, with more dainty features, and has relatively longer wings and a shorter and more squared tail with a much thinner white tip. Other slight difference may be noted in plumage via the sharp-shins lacking the capped appearance of adult Cooper's (being more hooded) and being generally slightly darker above. Juvenile sharp-shins, upon relatively leisurely study, can be seen to differ from juvenile Cooper's by having clearer supercilia, browner cheeks and less extensive whitish mottling above and also coarser streaking below extending more to belly. Bare parts, mostly distinguishable as well at close range, differ by the more centered and clearly relatively larger eyes and notably stick-like legs of the sharp-shins. However, often these features can often be difficult to impossible to discern when the hawks are seen in the wild. More distinctive in the field is the larger, more protruding head of the flying Cooper's hawks rather than the compact, rounded head of the sharp-shins which barely appear to exceed the leading edge of the wings in flight. Sometimes Cooper's is considered to look like a "flying cross" in comparison to the sharp-shins. Accipiter hawks of all species are seen mostly flying with quick, consecutive wing beats and a short glide (sometimes abbreviated as “flap-flap-glide”), though the species may also soar as well. However, the sharp-shinned hawk has a more buoyant flight with faster wing beats than Cooper's and soars with flatter wings (although again variations in the field make these characteristics far from foolproof).<p>As for the northern goshawk, the smallest male is still usually "clearly" larger than most large female Cooper's hawks. In the Goshutes mountains, migrant male goshawks overlapped with female Cooper's hawks only in the length of the tail and the tarsus, with the body mass especially being quite distinct. In Oregon, male goshawks averaged no less than 34% more massive than female Cooper's hawks, however the footpad of Cooper's females was almost the same size (7% larger on average in the latter) as the male goshawks (these may be features adapted to procuring birds as prey more so as bird-hunting raptors tend to have more elongated foot morphology). Proportionately, goshawks have longer, broader wings, shorter tail and a generally more Buteo-like form overall. Adult goshawks also have broad supercilia, pale gray color on the underside and a much darker coloring on the back. Given reasonable views, adult goshawks are very different looking and hard to mistake for any Cooper's hawk. Meanwhile, the juvenile goshawk is much paler edged above than the smaller Cooper's, including a panel formed along larger wing coverts. Below, juvenile goshawks have heavier streaks of a darker brown color than juvenile Cooper's. Also, the banding on the tail is off-set on goshawks, creating a zigzag effect on the tail, unlike the even barring on the juvenile Cooper's. Again, though, female Cooper's and male goshawks can come close to the same size and the not dissimilar juvenile plumage of the two species can lead to regular misidentification, especially to those with less prior experience viewing the more scarce goshawk. The most reliable way to distinguish a large juvenile Accipiter in the field are the differing proportions of the two species, followed by the heavier streaking below and irregular tail banding of the goshawk. For Cooper's hawk, there may be a possible and marginal overlap with the bicolored hawk (Accipiter bicolor) in southern Mexico and Central America. The latter species of similar form and size but at all ages is generally unmarked with bars or streaks below, also with a more or less uniform mantle. Vagrating migrant Cooper's hawks to Cuba may very rarely occur alongside another close relative, Gundlach's hawk (Accipiter gundlachi), which is quite similar in most aspects to Cooper's but is slightly larger with a darker hue about the back and the cap, a gray cheek, more dense and rich rufous color on the underside and wing panel in adults and darker and more heavy streaking in juvenile form. More unlikely to be mistaken for a Cooper's hawk are some buteonine hawks such as gray hawks (Buteo plagiatus), roadside hawks (Rupornis magnirostris) (in Mexico and points south) and broad-winged hawks (Buteo platypterus) which are all similar in size to Cooper's as well as the slightly larger red-shouldered hawk (Buteo lineatus). Even the most similar buteonine hawks have notably different proportions than a Cooper's hawk, possessing relatively much longer wings and a much shorter tail. Given reasonable views, all such species are fairly to extremely different in plumage even in juvenile form.

Taxonomía

Cooper's hawk was formally described by the French naturalist Charles Lucien Bonaparte in 1828 from a specimen collected near Bordentown, New Jersey. He coined the binomial name Falco cooperii. The specific epithet and the common name were chosen to honour the naturalist William Cooper, one of the founders of the New York Lyceum of Natural History (later the New York Academy of Sciences) in New York City. Other common names have been known to include the big blue darter, chicken hawk, hen hawk, Mexican hawk, quail hawk, striker and swift hawk. Cooper's hawk is a member of the genus Accipiter, sometimes referred to as true hawks (and the members of which are at times commonly referred to as goshawks or sparrowhawks). This genus is the most diverse of all in the species-rich family Accipitridae, with nearly 50 recognized species, and is also the most diverse of all diurnal raptor genera. The genus Accipiter appeared to diversify in the last few million years due to an increase in accessible avian prey. They appear to be a sister genus to Circus or harriers, albeit a distantly related one. Other smaller genera including Harpagus and Erythrotriorchis also appear to bear some relation. Genetic studies of three Asian Accipiter species showed that they may not be a monophyletic group, with various clades divisions outside traditional subfamily lines, with even the sharp-shinned hawk-like and aptly named tiny hawk (Accipiter supercilious) appearing to cluster outside of the genus nearer very dissimilar genera like Buteo and Milvus. It appears that Cooper's hawk was the earliest Accipiter to colonize North America with a well-defined fossil record dating back perhaps 0.5-1 million years. Fossil evidence shows then that the goshawk came second and, despite the considerably wider range of the sharp-shinned hawk compared to the other two species, the ancestors of the sharp-shinned hawk came over the Bering Land Bridge last. Genetic testing has indicated that Cooper's hawk is quite closely related to the northern goshawk, with the similar superficial characteristics of Cooper's to the sharp-shinned hawk, a close relative of the Old World sparrowhawk, apparently obtained through convergent evolution. A natural hybrid of a Cooper's hawk and a northern goshawk with intermediate physical characteristics was verified via genetic testing of a migrant juvenile in Cape May and was thought to indicate a northward expansion of Cooper's range into historic goshawk haunts.<p>No subspecies are recognized of Cooper's hawk. A previously described subspecies, A. c. mexicanus, was discounted due to being weakly differentiated. However, evidence based on genetic markers shows that westerly birds such those in British Columbia populations are genetically differentiated from those in the Upper Midwest, indicating that Cooper's hawk were restricted to at least two Pleistocene glacial refugia with the Rocky mountains acting as a natural barrier to gene flow between hawks on either side while breeding. Several of the other similar largish Accipiter species in the Americas appear to be closely related, possibly within a species complex, to Cooper's hawk, namely the bicolored hawk, widespread through Central and South America, and the Chilean hawk (Accipiter chilensis). While there is some degree of obvious differentiation from these species in appearance, distribution and behavior, more nebulous is the relationship of Cooper's hawk to the very similar Gundlach's hawk of Cuba. In general the relationship of Cooper's and Gundlach's hawk is muddled and genetic testing indicated that it is possible (but not certain) that Gundlach's may be insufficiently distinct to qualify as a separate species. It is almost certain that Cooper's hawk would at least qualify as the paraspecies for the Gundlach's and data has indicated fairly recent colonization and hybridization between the two hawks.

Nombre científico

Astur cooperii

Autoridad

(Bonaparte, 1828)

Orden

Accipitriformes

Familia

Accipitridae

Género

Astur

Distribución y hábitat

Cooper's hawk's breeding range extends from southern Canada to northern Mexico. In southern Canada, they breed (but do not normally winter) in the southerly parts of the provinces of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec to extreme southwestern Nova Scotia. They reach their northerly limits as a breeder roughly in Jasper National Park and Cedar Lake, Manitoba. Cooper's hawks live almost throughout the contiguous United States, excepting some parts of the southern Great Plains, as well as perhaps a bit of northwestern Maine and northernmost Montana. Their breeding range terminates just before the southern part of Gulf Coast states, south Florida, the southern tip of Texas and all but inland northwestern Mexico. Their Mexican breeding range consists of northern Baja California, the mountains from eastern Sonora and Chihuahua to Durango, also recently in northern Coahuila, formerly east into Nuevo Leon and south to Michoacán and possibly still in Guerrero. In Oaxaca, records show that the species has been recorded year-around with the first confirmed breeding reported in 2001. In winter, they are found up to the southern half of Washington, the southern two-thirds of Idaho and Wyoming, southern South Dakota, the southern parts of Minnesota, Wisconsin and Michigan, extreme southwestern Ontario, southwestern and southeastern New York and New England up through all but northwestern Massachusetts and to the southeastern part of New Hampshire. In winter they range regularly throughout the parts of the southern United States where they do not breed, such as all Gulf Coast areas and in south Florida. Wintering Cooper's hawks are common through essentially all parts of Mexico, becoming less regular around Guatemala and isolated spots of the border of Honduras and Nicaragua, where the species is considered "infrequent but regular" as well as in central and southern Costa Rica and perhaps northern Panama. Vagrants have been recorded in Colombia. There are several cumulative records of Cooper's hawks also appearing in Cuba at times of migration but generally the species is still considered a vagrant rather than a regularly occurring species there.<p>Cooper's hawks tend to occur in various types of temperate deciduous forest and mixed forest. They are also adaptable in all seasons to forested mountainous regions, especially foothills. The species may further make itself at home in some pure conifer forest, including the extreme southern part of the taiga but also in many parts of the west. The species can habituate favorably while breeding to various kinds of open woodlands, including small woodlots, riparian woodlands in dry country, pinyon woodlands, farmlands and floodplains. In fact, some authors felt the species increased locally in wooded parts of the Rocky mountains after human habitat fragmentation of once continuous woodland areas. Adaptability to forest fragmentation has also been reported in other parts of the range.<p>In denser forest areas, these hawks tend to prefer easy access to edges, clearings, roads and waterways. For example, average distance between waterways and nests in Wisconsin and Utah was 66.1 and 224 m (217 and 735 ft), respectively. However, in the Appalachians, there seemed to no detectable preference for access to water. Forest edges, in particular, tend to be key as these are peak hunting grounds for these hawks. Cooper's hawks usually occur at elevations from sea-level to 2,500 m (8,200 ft), more infrequently up to 3,000 m (9,800 ft). In the American southwest and northwestern Mexico, they are commonly considered a bird of wooded foothills, often dwelling above 1,000 m (3,300 ft). Although they often live in areas where deciduous trees are predominant, almost throughout the range they are often attracted to stands of conifers, which, due to their density, provide more extensive shelter and perhaps a more sturdy nesting site. Therefore, in areas such as Massachusetts and Wisconsin, they most often used stands of white pines (Pinus strobus). Additional Wisconsin studies showed that exotic conifer stands now support many Cooper's hawks even where native woodland is available. Tall, native deciduous tree stands may still be used extensively elsewhere, i.e. American beeches (Fagus grandifolia) in New York (nearly 40% of nest trees used) and oaks in Maryland (60% of trees used as nests). This species often prefers fairly mature forest, i.e. in two different areas of Oregon, Cooper's hawks preferred areas with trees of 30–60 years old (and 656 trees per ha) and 50–70 years old (and 1159 trees per ha), respectively. On average, the number of trees per hectare in Arkansas were found to be 935.7. Canopy coverage is key to nesting Cooper's hawks, needing to be at minimum about 55–70%, averaging 55% in Wisconsin and 69.8% in Arizona.<p>More so than breeding habitat, wintering habitat seems to be highly opportunistic. They may be found in any environment with some trees, including open woods, parkland and scrub areas. In Central America, wintering Cooper's hawks have been recorded in unusual habitats such as stunted cloud forest and treeless montane grassland. In most parts of the range, Cooper's hawks have shown to be somewhat adaptive to all gradients of human development, including urbanized areas and can even nest in many cities. They were once thought to be averse to cities and towns, but are now fairly common urban and suburban birds even when nesting. The species may even making use of isolated trees in suburbs, industrial parks and strip and shopping malls though large urban parks and other available wooded habitat is usually preferred in such areas when nesting. The cities provide plenty of prey species such as pigeons and doves and invasive species of bird for Cooper's hawk to prey on. Evidence from a well-studied population in the city of Tucson, Arizona shows that Cooper's hawks are now considerably more common within the city than elsewhere in the surrounding regions. Despite the success of Cooper's hawks in Tucson, attempts to find breeding activity in Phoenix and Casa Grande were unsuccessful, it is thought that the ambient temperature was too high or beyond thermal tolerance levels. Although more adaptable in habitat than the sharp-shinned hawk, studies from Pennsylvania have indicated that the species still more often than not prefers sizeable tracts of woodland for breeding and migrating to fragmented, developed areas. Similarly, in Tennessee, it was found for wintering Cooper's hawks that forested areas were 73% of the habitats used, which is far more prevalent than woodland available in the environs (with only 46% remaining wooded).

Migración

Complete migrants

Comportamiento

Cooper's hawk is a typical Accipiter in all respects. This species tends to be active earlier in the morning than sharp-shinned hawks and Eurasian sparrowhawks (Accipiter nisus) and is generally much more likely to be active in the morning than in the afternoon. These hawks may readily take to conifers to roost, generally sleeping with their heads tucked in. During daylight hours, they tend to preen while sitting on a perch about 11 times a day, and may take about 1–20 minutes to do so. When attaining water to drink, Cooper's hawks appear to prefer to come to relatively secluded waterways. In more arid regions, Cooper's hawks may seek out artificial bodies of water to drink from (especially in passage). Although a rare behavior, there are now several records of juvenile hawks of the species proning wherein they lie on their backs along a branch (or rarely the ground), apparently as a form of sunning. Cooper's hawks may come to walk on ground to gather nesting materials as well as to hunt. Cooper's hawks have a well-developed muscle mass that powers their flight, especially helping with acceleration during hunts and when carrying heavy prey. However, some other non-raptorial birds may have similar muscularity relative to their mass, such as the Canada goose (Branta canadensis) and even pied-billed grebes (Podilymbus podiceps), and these ample muscle masses may be correlated with migratory (rather than hunting) behavior. Cooper's hawks have been recorded as engaging in an exaggerated, nighthawk-like flight in non-courtship circumstances, such as during migration or by recent fledglings. During the late nesting stage, parent Cooper's hawks were recorded during daylight in Utah to engage in soaring flight 8.4% for males and 8.1% of the time for females with a further 6.4% and 2.8% of the time in different kinds of flights, perching the remainder of the time (about 2–6 minutes at each perch interspersed with brief flights). Another study found 13.7% and 10.7% of daylight at this later breeding stage to be in flight, the rest of time perching, with occasional inactive perching spells of around 15–40 minutes. However, that inactivity could last up to 5 hours during heavy rainfall. Breeding adults generally engage in agonistic behavior when an interloper of their sex is present; 11 responses showed that males responses consisted 64% of the provocations, 9% of the time by females and both members 27% of the time. Frequent aggressive interactions were recorded between females, often yearling and second year vs older females. Cooper's hawk's threat display appears to consist of them lowering their heads, raising their "crest" (capital tract), stretching out their wings, spreading the tail and engaging in vocalizations. Stress levels, as indicated by a study of corticosterone levels, were considered quite high when hawks are being handled by researchers, particularly in males (indicating that they experience higher levels of stress than females). Cooper's hawk is subject to frequent mobbing by various birds and some mammals, with good cause, but evidence shows that even main prey types like jays will sometimes shy away from engaging in full-fledged mobbing of a Cooper's, perhaps due to the risk in closely approaching this very agile predator, which can in an instant suddenly turn and kill a member of the mob. Therefore, less dangerous hawks such as Buteos are mobbed more vigorously than the more dangerous Cooper's. Many potential prey will confine their response to a hawk of this species to vocal scolding and/or attempt escape before an attack occurs.<p>Like a majority of diurnal birds of prey in the Northern Hemisphere, Cooper's hawk is a partial migrant. They tend to be most migratory in the north and largely to partially sedentary elsewhere. With individual exceptions, hawks of the species largely migrate out of nearly all of their range in southern Canada as well as cooler parts of the Pacific Northwest, essentially all of Montana and northern parts of surrounding states, the Dakotas (but for southern South Dakota), the northern parts of the Great Lake states, northern New York and much of New England. Despite being classed as sedentary, banding studies have revealed that many Cooper's hawks south of the typical migratory populations engage in some variety of seasonal winter movements. Migrants in the Florida Keys were determined via stable isotopes to have originated from mid-Atlantic states and the southeastern United States both (largely) south of the typical migratory range. While females in the urban areas of Tucson were sedentary (99%), about 6% of the females outside of the urban areas did not remain on their breeding grounds during winter. In British Columbia, many adults are non-migratory but juveniles do tend to migrate. From the Great Lakes region in particular, migrants appear to disperse in multiple directions to the south. Multi-directional movements, even to the north as well as potentially any other direction, are more common than previously thought in this and other migratory raptors, which has been previously described as "inefficient and indirect method of 'homing'". However, reaching regions where appropriate habitat and prey is available is probably far more significant in seasonal movements to birds of prey than climatic concerns. Fairly strong evidence has been found of habitual northbound migration by Cooper's hawks from Central and Southern California, usually over fairly short distances, often less than 320 km (200 mi). However, the three longest distance movements from southern California were all northbound, i.e. 616 to 993 km (383 to 617 mi). Cooper's hawks originating from Northern California do generally migrate south, mostly wintering in Mexico though sometimes covering up to 1,637 km (1,017 mi) to Central America. In Lansing, Michigan, evidence has been found of individual Cooper's hawks being annually devoted to the same wintering grounds, presumably due to their high quality.<p>Migratory movements in the autumn are generally between late August to mid-October, peaking at the end of September and beginning of October in the east, but sometimes migration extend into November. Meanwhile, spring northward migration may be any time from the end of February to May, with the last ones leaving Mexico in April and very late individuals were passing over south Texas in late May. Generally, spring migration is more dispersed and less consistent than fall migration. There is evidence from the Great Lakes region that spring migration is occurring sooner due to warming temperatures in recent years. Passage appears to be timed to coincide with that of their main prey, medium-sized birds. In migration, first-year juveniles precede two-year-old hawks which themselves precede adults when moving south in fall. Furthermore, females of all ages tend to migrate sooner and spend longer in winter quarters than like-age males, the latter staying relatively north and traveling back again earlier. Interestingly, the sharp-shinned hawk (despite the even more dimorphic migration times between sexes) showed no strong difference in distance on migration between the sexes, unlike female Cooper's which sometimes can move considerably further than males. At regular western migration sites, the average difference of passage timing for Cooper's hawks of the earlier females and later males of like-age was five days. In the Marin Headlands, migration of the sexes differed by 6 days in juvenile, first-year females and males and by 11 days in older females and males. Like other Accipiters (but unlike falcons), Cooper's appear to not start moving until day is warmer and thermals can be used. During migration they favor mountain ridges and coastlines, which coincide with migratory raptors routes in general. This species can seem to cross some bodies of water unlike most sharp-shinned hawks but seldom do so over wide bodies of water. However, they have been seen to turn up in such oceanic vicinities as the Florida Keys and Cuba, and so are capable of crossing larger than usual bodies of water. It is thought that Cooper's hawks also avoid the Great Plains while migrating as well. Like many other raptors, Cooper's hawks favor strong northwesterly winds during autumn passage.<p>At coastal migration sites like Cape May, first year Cooper's hawks are far more regularly encountered than older individuals, with the juvenile Cooper's accounting for 92.7% of recorded individuals of the species (juveniles of various other raptor species also generally seem to favor coastal over montane migration when it is available). In Cape May, Cooper's hawks are the third most commonly recorded raptor species in passage behind the sharp-shinned hawk and the American kestrel (Falco sparverius) but are far less than numerous in migration or in winter in the nearby Delaware Bayshore locations of New Jersey than various other raptor species. Interestingly, in the Manzano Mountains and Goshute Mountains, juvenile sharp-shinned hawks were roughly twice as numerous as juvenile Cooper's hawks but the number of adults seen passing through of the two species was roughly the same. At the hawkwatch in Cedar Grove, Wisconsin, Cooper's hawk was not among the most regular species, being the 6th most frequently most recorded species. In central and southwestern Idaho, Cooper's hawk accounted for relatively few of the recorded raptors, i.e. 3.45% of 748 migrating raptors. A similarly low volume was observed relative to other bird of prey species in Yellowstone National Park, where Cooper's was only the 9th most frequently observed out of 17 species and averaged only 50 hawks in passage over the course of autumn. Nonetheless, Cooper's hawk was second only to sharp-shinned hawk as the most frequently recorded species seen migrating at nine major hawkwatchs throughout the western United States (and 1 in Canada) and, unlike the sharp-shinned, has shown a trend of increase in numbers overall in recent decades, despite some declines in numbers at Lipan Point and Bridger Range. Cooper's hawk was the 7th most often recorded raptor at four migration sites along the Gulf Coast, being much more frequently identified in the site at Veracruz, Mexico than the ones in the United States, but showed an annual stability of numbers that many of the more numerous raptors (including sharp-shinned hawks) in passage did not. Along the Kittatinny Ridge in Pennsylvania, studied Cooper's hawks that were migrating from further north spent only 12% of the day actually migrating, devoting the remainder of their time to perching and hunting along their passage. Fat stores were measured to consist of 4–12% of the body mass of migrants, being higher in autumn than in spring, and higher on average in adults over younger hawks and in females over males. Migration speeds appear to be largely similar to those of other raptors, with average speeds of 33.6 to 88 km/h (20.9 to 54.7 mph), but one migrating from Colorado was recorded to cover about 26 km (16 mi) per day. Typically Cooper's hawk migrate singly but sometimes can be seen in groups of two to five. Flocking is not typically engaged in by raptors who migrate using powered flight, such as Accipiters, falcons and harriers, but many Buteo hawks do form loose flocks. 96.3% of 806 observed Cooper's hawk seen migrating in Johnson County, Iowa were solitary, although 30 migrating pairs were seen together.

Conservación

Cooper's hawks have had an erratic status throughout the 20th into the 21st centuries. Historic data shows a threefold increase, roughly, around 1920. However, mortality rates shot up soon after as some authors consider the annual rate of mortality due largely to legalized direct persecution (poisoning, "pole trapping" and, especially, shooting) between 1925 and 1957 could range up to 60.5–77.6% in the most severe years. The amount of hawks shot down within different populations was estimated at 12 to 40%. Migration counts during the 1930s showed a strong downward trend, and an even worse decline for Cooper's hawk was observed during the late 1950s. Most Cooper's hawks reacted to heavy persecution by behaving with more shyness and elusiveness. Much of the human animosity towards Cooper's hawks was due to their hunting of gamebirds such as quail which human hunters themselves coveted. Furthermore, even ornithological writings from these times reveal a strong bias against the hawks for their hunting of admired small birds. However, several studies have determined that Cooper's hawk predation is not detrimental to healthy gamebird population, and that most of the blame must fall directly on overexploitation and habitat destruction of humans themselves, with a more recently quantified causal of changing climate further exacerbating the gamebirds' declines. Human hunting of Cooper's hawk declined when governmental protection of the species was instituted in the late 1960s (nearly two decades after some less controversial birds of prey species were protected in America).<p>However, instead of the expected gradual recovery, in the 1960s to 1970s, the breeding success rate dropped, in almost certain correlation with man's use of chemical biocides, mostly DDT. Raptorial birds which predominantly prey on either birds or fish were severely affected by the DDT biocide. The concentrations of organochlorines like DDT were high in all American Accipiters, averaging at intermediate levels in Cooper's (0.11 mg/kg) but could include the highest known in the Accipiters at up to 1.5 mg/kg. A considerable average reduction in eggshell thickness was measured to average at around 7%. A particularly severe reduction in eggshell thickness was recorded in New York state, at an average of 19.02%. The survival of the species, especially in the eastern part of the continent, was seriously questioned in the 1960s and 1970s. Fewer dramatic ebbs were detected during the height of DDT use in the western part of North America overall, perhaps because of less overall reliance on bird prey. Nonetheless, 11 of 16 eggs in Arizona and New Mexico broke due to this cause. Subsequent to the prohibition of DDT use in North America, the population increased exponentially in the 1980s and 1990s and ultimately was thought to stabilize. Data from Hawk Mountain Sanctuary shows that Cooper's hawk has recovered from DDT more gradually than the sharp-shinned hawk here.<p>In the 1990s, it was estimated that Cooper's hawks may number "well into six figures" due to their regular distribution over 8 million square kilometers. Today, Cooper's hawk is thought to number around 800,000 in the United States and Canada. These estimates were gained cross-referencing the number of hectares per active nest, which was in the range of 101 to 2,326 ha (250 to 5,750 acres) in the western states and 272 to 5,000 ha (670 to 12,360 acres) in the Midwestern and eastern states, as well as data from Christmas Bird Counts and migration counts. Evidence from long-time migration counts at Bake Oven Knob show slight peaks at intervals of 3 to 4 years, however no dramatic declines have been detected since the 1980s. Following their historic decline, Breeding Bird Surveys have tracked strong increases of the breeding population (upward trends from 1.2% in California to 4.4% in Pennsylvania) in six states, with a 2.2% increase overall, and similar trends in multiple other states. In many states (Arizona, California, Florida, Missouri, New Mexico and North Dakota) the numbers are probably similar or greater to those prior to 1945. It is thought that the population of Cooper's hawks in Wisconsin is nearly saturated relative to the landmass of the state, after a rough 25-fold increase since the late 1970s. Based largely on data from well-known populations such as Tucson and Milwaukee, some authors opine that Cooper's hawk may be the most common raptor in American urban areas today, although surely other common raptorial birds such as red-tailed hawks, American kestrels and turkey vultures (Cathartes aura) may easily rival them in this regard.<p>Shooting is now a generally insignificant cause of mortality though is still sometimes reported. Despite the declining effect of pesticides on Cooper's hawk's overall population, lingering harmful effect from dieldrin has been indicated in some hawks in British Columbia and recently some hawks have been killed by the pesticide warfarin. Bioaccumulation of pollutants may still have considerable effect on this species. Declines due to pollutants are seemingly occurring for Cooper's hawks living in Vancouver. Recent cases of cyanide poisoning of Cooper's hawks have been reported. Lead poisoning can sometimes threaten Cooper's hawks, through lead bullets left in dead or injured game.<p>Most urban-related mortality for Cooper's hawks is likely to be collisions with manmade objects. These are mostly wire strikes (with or without resulting electrocution), automobile collisions and window strikes or with other parts of manmade structure while distractingly hunting. 70.8% of diagnosed mortality for Cooper's hawks of yearling age or older in Tucson was from such collisions. In less developed regions, such as much of Montana, the rate of wire collisions and electrocutions was considerably lower for Cooper's hawks than for various other birds of prey who are either larger-bodied and/or use less forested areas. Other studies support that the number of fatal window and wire collisions of urban-living Cooper's hawks is "excessively high". Cooper's hawks found in the vicinity of airports are at risk of bird strike with aircraft, therefore 185 Cooper's were translocated away from these areas (the 5th most frequently translocated raptor species). A similar translocation effort away from the Los Angeles basin around the Los Angeles International Airport translocated 349 Cooper's hawks (about a fifth of all translocated raptors), apparently successfully. Cooper's hawks are sometimes displaced by the placement of wind farms, with studies indicating that Cooper's need about seven years to locally recover from such displacement. Synurbization has been detected in Cooper's hawks as, despite the dangers of various kinds of collisions, it has been found that in favorable urban areas, hawks of the species can seem to breed more closer to one another, gather more food and produce more young on average than those outside such areas. Even New York City has seen (if erratically present) since the late 1990s, a return of nesting Cooper's hawks.<p>Logging may decrease some populations but the overall effect it has on Cooper's hawks is generally considered unknown. As with all Accipiters, Cooper's hawks can presumably only withstand a certain level of loss of habitat before an area becomes essentially unlivable. Studies in Arizona determined that heavily grazed agricultural areas were favored over lightly grazed ones due to greater prey concentrations in the latter habitats. On the contrary, in the early 1990s (while the species was generally recovering), the species was considered to be "state-endangered" in New Jersey, with ongoing harmful effects found for poorly-regulated (or entirely unregulated) logging and land development within 40 to 120 m (130 to 390 ft) of active nests. In the Black Hills, harvesting of ponderosa pines appears to be causing Cooper's and both other species of Accipiter to vacate large parts of the forest. It has been recommended that a buffer zone of at least 200 to 240 m (660 to 790 ft), with a median estimated space needed of about 525 m (1,722 ft), should be free from human disturbance or development to retain the protected nests of Cooper's hawks. Studies in New Mexico showed that these hawks are reliant on the conservation of riparian woodlands in much of the southern part of the state. Despite the large, productive and genetically diverse population of Cooper's hawks in Tucson, several authors have hypothesized, controversially, that the city is an ecological trap, due to the unsustainably high turnover for nestlings via Trichomoniasis-related mortality and for adults via frequent lethal collisions.<p>Quite few Cooper's hawks have ever been gathered for use in falconry. This hawk is fairly unpopular in falconry practices due to its high-strung personality and is additionally considered in such captive conditions as given towards "tyrannical", "hysterical" and "demanding" behaviors, even compared to its similarly disposed larger cousin, the northern goshawk, which is fairly popular in falconry.<p>Generally, Cooper's hawks hunt the locally common birds that are available and probably control some birds (such as the more numerous icterids and corvids) that may without the influence of natural predation risk overpopulation and potential harm to ecosystems. However, as an opportunistic natural predator of almost any North American bird smaller than itself, Cooper's hawk may inadvertently deplete populations of rarer, conservation-dependent species. The American kestrel, whose populations have experienced considerable decrease, may be one species which has suffered from the extensive predation of the recovered Cooper's hawk population. However, there is no evidence that Cooper's hawk predation is one of the leading causes of kestrel declines and data seems to indicate it is, at most, a localized threat. Similarly, Cooper's hawks occasionally prey upon other threatened bird species, and, although said predation is not a primary cause of concern, may exacerbate the already worrying condition of many declining North American birds. Some threatened species known to be thusly hunted by these hawks are greater prairie chicken (Tympanuchus cupido), lesser prairie chickens (Tympanuchus pallidicinctus), red-headed woodpeckers, Bell's vireo (Vireo bellii), Florida scrub jay (Aphelocoma coerulescens), wood thrush (Hylocichla mustelina) (Cooper's being identified as one three major nest predators along with blue jays and raccoons), golden-winged warbler (Vermivora chrysoptera), cerulean warbler (Setophaga cerulea) and golden-cheeked warbler (Setophaga chrysoparia).

Tendencia poblacional

rising