(or Accipitriformes, q.v.)
Asturina nitida plagiata
The grey hawk (Buteo plagiatus) is a smallish raptor found in open country and forest edges. It is sometimes placed in the genus Asturina as Asturina plagiata. The species has recently split by the AOU from the grey-lined hawk. The grey hawk is found from Costa Rica north into the southwestern United States.
The grey hawk is 46–61 cm (18–24 in) in length and weighs 475 g (16.8 oz) on average. The adult has a pale grey body, the tail is black with three white bands and the legs are orange. It is a solid, unpatterned gray on the upper parts.
Immature birds have dark brown upperparts, a pale-banded brown tail, brown-spotted white underparts and a brown streaked buff head and neck. This species is quite short-winged, and has a fast agile flight for a Buteo. The call is a shrill whistled kleee-ooo.
Grey hawks feed mainly on lizards and snakes, but will also take small mammals, birds and frogs. It usually sits on an open high perch from which it swoops on its prey, but will also hunt from a low glide. The nest is of sticks and built high in a tree. The usual clutch is one to three, usually two white to pale blue eggs. The young take about 6 weeks to fledging.
The taxonomy of the grey hawk puts it within in the genus Buteo. This genus consists of hawks, which include the red-shouldered hawk, Swainson's hawk, and others. The genus Buteo is in the sub-family Accipitrinae which is also known as the “true hawks,” and Accipitrinae is within the family of Accipitridae. Accipitridae consist of hawks, old world vultures, kites, harriers, and eagles. This family is within the order Falconiformes which are the diurnal, meaning during the day, birds of prey.
The grey hawk was originally Asturina nitida but controversy existed between ornithologists on whether or not this species was closely enough related enough to put it in the Buteo, but chromosomal mapping in 2013 has proved that the grey hawk is within the Buteoninae. Researchers such as de Oliveira, Tagliarini, dos Santos, O'Brien, and Ferguson-Smith proposed in 2011 that the gray hawk should be two different species, because of a slight difference in plumage colour and a difference in alarm calls documented in the northern and southern distributional gap in Costa Rica. They suggest that the species is better split into the grey-lined hawk, Buteo nitidus and the grey hawk Buteo plagiatus), but the American Ornithologist Union does not recognize the grey hawk as two different species. So far under the size range criteria this species' population is not vulnerable.
The grey hawk averages 46–61 cm (18–24 in) inches in length and weighs 475 g (16.8 oz). This bird has a relatively short wing span, but long tail compared to the red-tailed and red-shouldered hawks. It has broad rounded wings, a hooked beak, and yellow legs.Thompson, L. (1995-2013). It is very distinctive from its smooth pale grey plumage. The tail features are in a horizontal stripped pattern in a white gray white pattern with white at the tips of the tail feathers. The tail feathers have two white bands with one being wider than the other. The sexes are similar in coloration. The adults, both male and female, have a darker grey top side with a lighter grey and white underside. The juveniles have a dark brown topside and a streaked or spotted underside and the tail feathers have numerous dark bands. The juveniles have very obvious bold facial strips and white upper tail coverts, which are the feathers at the base or start of the tail. The juveniles also have a different plumage colour due to dominance and they use the dull colour for camouflage.
Distribution and habitat
A grey hawk’s range for the most part is in Central America and extends down into the Amazon and Northern Argentina in South America. The range also can extend north into northern Mexico, southern New Mexico, southern Arizona, and southern Texas. Its habitat within this range consists of forest edges, river edges, clear cuts, savanna, and agricultural land (4). In their tropical range of the Amazon they tend to prefer a more dry second growth forest.
The grey hawk’s main diet is lizards and small birds, but it will also eat rodents and large insects. It hunts in brushy areas either from a perch or flight just above the canopy.
The migration of the gray hawks depend on the location in which a that animal’s home range is in. Birds that live in south-western United and Northern Mexico will migrate, but birds living further south are permanent residential of that area. In a few occasions some birds in the northern range will not migrate and stay in the southern part of Texas year round, but this is rare. The birds that migrate north to the south-western United States will migrate in the spring in order to breed. After breeding season the birds will begin their journey back south in mid October to their wintering ranges.
The mating system of the grey hawk is monogamous. During December through May, the breeding season, these birds perform courtship displays (4). The males court the females by rising and falling flight, calls, and nest building. The male and female together will build their stick nest in tall trees, but the male only lays down the foundation while the female will shape the nest (9). The nest is about 60 centimeters across and the female will on average lay 2 to 3 pale-blue eggs per clutch. The female takes care of her eggs incubating them for 33 days; meanwhile the male will capture prey and bring it back to the female. A few breeding pairs nest along the Rio Grande in riparian woods (1). In research conducted from 1995-97 in south-west Arizona, it was found that gray hawks produced an average of 1.32 young per nest between all three years when the study was being conducted (8). The chicks will begin fledging in 6 weeks and both males and females won’t hit sexual maturity until they are least 2 years of age.
The call of the grey hawk consists of long mournful whistles thoooooweeo, hoooooweeo .
- BirdLife International (2012). "Buteo nitidus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- "Animal Diversity (Asturina nitida)". Retrieved 2008-06-26.
- The American Ornithologist Union. (2013). List of the 2,046 Bird Species (With Scientific and English Names) Known From the A.O.U. Check-List Area. The American Ornithologist Union. Retrieved November 10, 2013
- de Oliveira E.H.C, Tagliarini M.M, dos Santos MS, O'Brien P.C.M., Ferguson-Smith M.A. (2013) Chromosome Painting in Three Species of orButeoninae: A Cytogenetic Signature Reinforces the Monophyly of South American Species. PLOS ONE.
- Millsap, B.A, Seipke S.H., Clark W.S. (2011). The Gray Hawk (Buteo Nitidus) is Two Species. Condor. 113(2), pp. 326–339.
- Sibley, A. D., 2003. The Sibley Field Guide to Birds of Eastern North America. Andrew Stewart Publishing Inc. pp 101.
- Buteo nitidus Gray Hawk Asturina nitida. Discover Life. Retrieved November 7, 2013
- Rodríguez-Flores, C., Soberanes-González C., and Arizmendi M.C. (2010). Buteo nitidus. The Cornell Lab of Ornithology Neotropical Birds. Retrieved November 7, 2013
- Bibles B.D., & Mannan R.A. (2004). Productivity and Nest-site Characteristics of Gray Hawks in Southern Arizona. Journal of Raptor Research. 38(3). pp. 238–242