Short-tailed Hawk

Short-tailed Hawk
Adult flying in São Paulo, Brazil
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Subclass:	Neornithes
Infraclass:	Neognathae
Superorder:	Neoaves
Order:	Falconiformes (or Accipitriformes, q.v.)
Family:	Accipitridae
Genus:	Buteo
Species:	B. brachyurus
Binomial name
Buteo brachyurus Vieillot, 1816
Synonyms
Buteo fuliginosus

The Short-tailed Hawk (Buteo brachyurus) is an American bird of prey in the family Accipitridae, which also includes the eagles and Old World vultures. As a member of the genus Buteo, it is not a true hawk and thus also referred to as a "buteo" or (outside North America) "buzzard". The White-throated Hawk (B. albigula) is a close relative and was formerly included in the species B. brachyurus.

Description

The Short-tailed Hawk is a small buzzard. Males average smaller than the females, but the size difference is slighter than in most birds of prey and the sexes are indistinguishable in the field. Length can range from 37 to 45 cm (15 to 18 in), wingspan from 80–103 cm (31–41 in) and body mass from 342 to 625 g (12.1 to 22.0 oz). Among standard linear measurements, the wing chord is 26.5–34 cm (10.4–13.4 in), the tail is 13–18 cm (5.1–7.1 in) and the tarsus is 5.5–6.2 cm (2.2–2.4 in).^[2] It has broad rounded wings, the tips of which are curved upwards while soaring, and a broad tail that despite the bird's name is of average length for a buteo in proportion to the body. Its call is a high-pitched scream similar to other buzzards.

One of the most interesting things about this bird is the melanistic "black" phase – this species occurs in two colour morphs, with no intermediates. The dark form predominates in Florida, where it is known as "little black hawk". The light form is common elsewhere in the species' range. In most of the North American buteos – e.g. the Red-tailed Hawk (B. jamaicensis) and Swainson's Hawk (B. swainsoni) – melanistic individuals are known, although wholly black plumage is comparatively rare. Only in the North American population of Buteo brachyurus does it seem to be the prevalent form.

The adult light morph has dark brown upperparts. The underparts are white, except that the tail and flight feathers are grey barred with dark. The immature is similar to the adult but the face is streaked rather than white, and the tail bands are of equal width, whereas the adult has a broad bar near the tail tip. The light morph is considered unmistakable when seen well in flight, due its blackish back and hood in contrast to an otherwise largely white underside.^[2]

The adult dark morph has black-brown upperparts and underparts, apart from the tail and flight feathers, which are grey barred with dark as in the light morph but possibly with darker grey. The young bird has the same tail pattern as the light-morph immature, and the underparts are spotted with white. Differentiating the dark morph from other dark morph Buteos is difficult, especially from the closely related Broad-winged Hawk.^[2]

For a long time, it was thought that the dark phase of the present bird was a distinct species Buteo fuliginosus. For example, when Robert Ridgway discussed the Short-tailed Hawk collected at Oyster Bay, Lee County, Florida by W. S. Crawford on January 28, 1881, the question whether or not the black birds were of the same species as the light ones was not yet settled.^[3]

Range and ecology

Short-tailed hawks breed in the tropical and subtropical Americas from southeastern Brazil and northern Argentina north through Central America to northern Mexico, as well as in southern Florida, USA. This species is generally found below 4,500 ft (c. 2,000 meters) ASL and most common below 2,500 ft (c.1,400 meters). It is replaced by the White-throated Hawk (B. albigula) in the Andes of southern Colombia and south to central Argentina and Chile; the Short-tailed Hawk is found in the Cordillera Central and Cordillera Occidental of Colombia, while B. albigula occurs south of these locales.^[4] As far as is known, B. brachyurus is a year-round resident except that most of the Florida population migrates in winter to the southern tip of the state, including the Keys. It is somewhat habitat adaptable but only passes areas with dense human populations when foraging. The species may be found in wooded savannah, patchy woodlands near water, cypress swamps, mangrove swamps or high pine-oak woodlands. In the tropics, it is most common in lowland foothills.^[2]

Most of what is known about its natural history has been studied in the Floridan population, and might not apply to birds at the south of the species' range. In general, this species is associated with woodland, often near water.

In Florida, it eats mainly smaller birds. The Short-tailed Hawk hunts from soaring flight, often at the borders between wooded and open areas. A frequent maneuver is "kiting" – coming to a stop, the bird heads into the wind, with its wings held stationary. It typically attacks prey with a nearly vertical swoop, sometimes pausing and then continuing downward in a "stair-step" manner. Typical prey ranges from a New World warbler (Parulidae) to a bobwhite (Colinus) in size. In Florida, icterids – namely the Red-winged Blackbird (Agelaius phoeniceus), the Common Grackle (Quiscalus quiscula), the Boat-tailed Grackle (Quiscalus major) and the Eastern Meadowlark (Sturnella magna) – make up the bulk of the prey. In one case, 95% of a single hawk's prey selection was found to consist of Red-winged Blackbirds.^[5] Hunting success is apparently relatively low. In one study, 30 hours of observation showed that only 12 of 107 hunting attempts (or around 11%) were successfully.^[6] There are isolated records of Short-tails predating Sharp-shinned Hawks (Accipiter striatus) and American Kestrel (Falco sparverius). Among tropical populations, they are several records of this species regularly taking frogs (especially tree frogs), lizards, large insects such as wasps and locusts. Such prey, which serves merely as alternate foods for Florida populations, apparently provides a much large portion of the diet in tropical populations. In all parts of the range they occasionally supplement their diet with smallish mammal, principally small rodents such as mice or rats. Among the heaviest prey recorded are young Common Marmosets (Callithrix jacchus) and similar small monkeys; these do not seem to form an important prey item however, and are only snatched when the opportunity presents itself.^[7] They are primarily an aerial predator, taking most prey by swooping down to trees or the ground. Rarely, they have been also record still hunting from a perch.^[2]

The large stick nest is built in a tree, at a height ranging from 2.5 to 30 m (8.2 to 98.4 ft). In Florida, the Bald Cypress (Taxodium distichum) is a popular nesting tree of the Short-tailed Hawk. The nest is bulky, measuring 60–70 cm (24–28 in) wide and 30 cm (12 in) deep. Its 1–3 eggs prer clutch are white, usually with dark spots and blotches. The nesting season is January through June in Florida and is possibly similar in the tropics. Incubation occurs over 34 days with no known details of their fledgling period.^[2] In Florida, American Crows have been known to consume eggs of this species.^[8]

The Short-tailed Hawk is uncommon and local in most of its range. It is quite difficult to detect unless in flight, since it is often concealed while perched by dense canopy or with only the head showing (unlike most Buteo hawks which generally prefer prominent perches). Due to the fact that it is believed to be regularly overlooked in the field, no comprehensive population surveys have occurred for the species.^[2] However, due to its wide extent of occurrence, it is not considered threatened by the IUCN.^[1] Sightings of soaring Short-tailed Hawks are fairly frequent within their range.

References

Further reading

Wikimedia Commons has media related to Buteo brachyurus.

• Hilty, Steven L. (2003): Birds of Venezuela. Christopher Helm, London. ISBN 0-7136-6418-5
• Miller, Karl E. & Meyer, Kenneth D. (2004): A Closer Look: Short-tailed Hawk. Birding 36(5): 478–487