Sharp-shinned Hawk

The sharp-shinned hawk is sometimes separated into four species, with the northern group (see distribution) retaining both the scientific name and the common name sharp-shinned hawk (A. striatus). In addition to the nominate taxon A. s. striatus on Hispaniola, it includes the subspecies A. s. perobscurus on Haida Gwaii, A. s. velox in most of mainland North America, A. s. suttoni in northern Mexico and southern New Mexico, A. s. madrensis in southwest Mexico, A. s. fringilloides on Cuba, and A. s. venator on Puerto Rico. The three remaining taxa, each considered a monotypic species if split, are the white-breasted hawk (A. chionogaster Kaup, 1852 in southeast Mexico and Central America), plain-breasted hawk (A. ventralis Sclater, 1866 in the Andes) and rufous-thighed hawk (A. erythronemius Kaup, 1850 in southeastern South America). The breeding ranges of the groups are entirely allopatric, although the wintering range of the nominate group partially overlaps with the range of A. chionogaster (as is also the case with certain taxa within the nominate group). This allopatry combined with differences in plumage (see Appearance) and, apparently, certain measurements, has been the background for the split, but hard scientific data are presently lacking (AOU). Most material published in recent years (e.g. AOU, Ferguson-Lees et al. p. 586, and Dickinson et al.) has therefore considered all to be members of a single widespread species – but not without equivocation: Ferguson-Lees et al. say that if they were to make a world list, they would include the three taxa as separate species (p. 75), and the AOU's comment includes the note "split almost certainly good". Storer (1952) suggested that the southernmost populations within the nominate group were paler below, thus approaching A. chionogaster. This has also been reflected in recent guides, where A. s. madrensis of southern Mexico is described as being relatively pale below (compared to more northern subspecies), but if this is a sign of intergradation with A. chionogaster or a north-south cline which includes both the members of the nominate group and A. chionogaster remains unclear. In Bolivia, A. ventralis and A. erythronemius approach each other, but no evidence of intergradation is known, something that, without actual specimens, would also be hard to prove due to the variability in the plumage of A. ventralis. A 2021 study of sharp-shinned hawks recommended recognising the three endemic Caribbean island subspecies as distinct species, based on analysis of their nuclear and mitochondrial DNA showing no modern contact between them, and diagnosed by their plumage; A. striatus, restricted to the island of Hispaniola, A. fringilloides to Cuba and A. venator to Puerto Rico. If this is accepted and A. striatus treated as endemic to Hispaniola, the continental complex then takes the scientific name A. velox.

This species is widespread in North America, Central America, South America and the Greater Antilles. Below, the distributions of the four groups (see Taxonomy) are described as they occur roughly from north to south: * The nominate (A. s. striatus) group is widespread in North America, occurring in all of the forested part of USA and Canada, breeding in most of it. Populations in the northern part of the range migrate south and spend the non-breeding season (winter) in the southern USA, Mexico and Central America as far south as Panama, with a smaller number spending the winter in the Greater Antilles. Resident populations exist in temperate parts of the US, Canada (in a few coastal regions), Mexico (highlands from Sonora to Oaxaca), Cuba, Hispaniola and Puerto Rico. * A. (s.) chionogaster (white-breasted hawk) occurs in highlands from far southern Mexico (Chiapas and Oaxaca), through Honduras, Guatemala and El Salvador, to Nicaragua. It is, as far as known, resident, but some local movements may occur. * A. (s.) ventralis (plain-breasted hawk) occurs in the coastal mountains of northern Venezuela and Colombia, south through the Andes from western Venezuela, through Colombia, Ecuador and Peru, to central Bolivia. A disjunct population occurs in the Tepuis of southern Venezuela (likely to extend into adjacent parts of Roraima in far northern Brazil, but this remains unconfirmed). It is, as far as known, resident, but some local movements may occur. * A. (s.) erythronemius (rufous-thighed hawk) is widespread in eastern South America in eastern and southern Brazil, Uruguay, Paraguay, north-eastern Argentina and south-eastern Bolivia. It is, as far as known, resident in some regions and migratory in others. The movements are generally poorly understood, but it only occurs seasonally at some localities in Argentina.

Sharp-shinned hawks construct a stick nest in a large conifer or dense group of deciduous trees. Clutches of 3 to 8 eggs have been recorded, but 4 to 5 eggs is the typical clutch size. The eggs measure and weigh about . The eggs are heavily marked with colourful and varied markings. The incubation period is thought to average at about 30 days. After hatching, the young are brooded for 16 to 23 days by the female, while the male defends the territory and catches prey. The young fledge at the age of about a month and rely on their parents for feeding and protection another four weeks. The nesting sites and breeding behaviour of sharp-shinned hawks are generally secretive, in order to avoid the predation of larger raptors, such as the American goshawk and the Cooper's hawk. While in migration, adults are sometimes preyed on by most of the bird-hunting, larger raptors, especially the peregrine falcon. The breeding behaviour of the taxa chionogaster (white-breasted hawk), ventralis (plain-breasted hawk) and erythronemius (rufous-thighed hawk) are comparably poorly known, but based on the available knowledge they appear to differ little from that of the nominate group In Puerto Rico, sharp-shinned hawks may be eaten by some growth stages of invasive boa constrictors.

]] In North America this species declined in numbers in the 1960s and 1970s, probably as a result of the use of DDT and other pesticides. The population of USA and Canada has rebounded since and might even exceed historical numbers today, probably due to the combination of the ban on DDT and the proliferation of backyard bird feeders in North America which create unnaturally reliable and easy prey sources. Migratory sharp-shinned hawks are one of the most numerous raptors recorded at "hawk watches" across the country. An exception is the subspecies from Puerto Rico, Accipiter striatus venator, which is rare and listed as endangered by the U.S. Fish & Wildlife Service. The remaining resident subspecies from the Greater Antilles, fringilliodes from Cuba and nominate (A. s. striatus) from Hispaniola, are uncommon, local, and, at least in the case of the latter, decreasing. Both ventralis (plain-breasted hawk) and erythronemius (rufous-thighed hawk) are fairly common (but easily overlooked due to their secretive behaviour) and presently considered safe. The situation for chionogaster (white-breasted hawk) is potentially more problematic due to its limited range, although it, at least locally, remains fairly common.

* "[https://www.biodiversitylibrary.org/page/20733374 Falco pennsylvanicus, Slate-coloured Hawk]", "[https://www.biodiversitylibrary.org/page/20733376 Falco velox, Sharp-shinned Hawk]"; in American Ornithology 2nd edition, volume 1 (1828) by Alexander Wilson and George Ord. [https://web.archive.org/web/19990507165125/http://xroads.virginia.edu/%7EPUBLIC/wilson/46.html Colour plate] from 1st edition by A. Wilson. * "[https://www.biodiversitylibrary.org/page/33238666 Sharp-shinned or Slate-coloured Hawk], Falco fuscus Gmel." John James Audubon, Ornithological Biography volume 4 (1838). [https://www.biodiversitylibrary.org/page/40383123 Illustration] from Birds of America octavo edition, 1840. * "[https://www.biodiversitylibrary.org/page/5886248 American Brown or Slate-colored Hawk]", Thomas Nuttall, A manual of the ornithology of the United States and of Canada; volume 1, The Land Birds (1832). sharp-shinned hawk Category:Birds of North America Category:Birds of Central America Category:Birds of the Northern Andes Category:Birds of Brazil Category:Birds of the Dominican Republic Category:Birds of Paraguay Category:Birds of Uruguay Category:Birds of Argentina sharp-shinned hawk Category:Birds of prey Category:Birds of prey of North America sharp-shinned hawk sharp-shinned hawk