Western red-tailed hawk

The western red-tailed hawk (Buteo jamaicensis calurus)[1] is a subspecies of the red-tailed hawk.

Western red-tailed hawk
Red-tailed Hawk
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Accipitriformes
Family:	Accipitridae
Genus:	Buteo
Species:	B. jamaicensis
Subspecies:	B. j. calurus
Trinomial name
Buteo jamaicensis calurus Cassin, 1855

Description

In wing chord males range from 354 to 404 mm (13.9 to 15.9 in), averaging 386.8 mm (15.23 in), and females range from 386 to 428 mm (15.2 to 16.9 in), averaging 411.2 mm (16.19 in). males and females average 224.2 and 237.3 mm (8.83 and 9.34 in) in tail length, 85.4 and 88.1 mm (3.36 and 3.47 in) in tarsal length and 25.1 and 27.4 mm (0.99 and 1.08 in) in culmen length.[2][3][4][5] The two largest samples of body mass in B. j. calurus showed that in Idaho, around the greater area of the Snake River NCA, 90 males averaged 957 g (2.110 lb) and 113 females averaged 1,150 g (2.54 lb), while 152 migrating B. j. calurus at the Goshute Mountains of Nevada averaged 933.4 g (2.058 lb).[6][7] Adult B. j. calurus are usually rangier and darker than the eastern red-tailed hawk (B. j. borealis), with pale individuals usually having a richer tawny base color (with occasionally a pale rufous color showing around the chest or neck), typically a heavily streaked breast and belly band, a brownish throat, dark barring on the flanks, a well-defined tawny V on the back and, occasionally, a tail with multiple bars. Dark morph B. j. calurus adults are typically all chocolate brown above and below (although sometimes variously even jet black or with a bit of tawny feather edging below) with a rufous tail, which sometimes has heavy blackish crossbars but is usually similar to other red tails. Intermediate or rufous morphs are rich rufous on the breast, with a broad, solid chocolate-brown belly band and heavily barred thighs and crissum. Like dark morphs, rufous morph adults usually lack the incomplete V on the back, but sometimes rufous feathers can manifest on one. Adults may show nearly endless variation in coloring and many may combine several characteristics of the three main morphs. Dark morph juveniles are usually mostly dark brown but with extensive pale mottling on the back and occasional tawny-edge feathers on the underside and slightly broader bars on the tail than pale morph B. j. calurus. Rufous morph immatures are more similar to pale morph ones but are considerably more heavily streaked almost everywhere below from the thighs to the upper chest.[2][3] Individuals of northwestern Mexico may average paler than most B. j. calurus, lacking the typical dark wing markings.[8]

Distribution

This race seems to have the greatest longitudinal breeding distribution of any race of red-tailed hawk, and put together with B. j. borealis these two subspecies may occupy nearly 75% of the breeding range of red-tailed hawks in North America.[9][10] B. j. calurus reaches its northern limits as a breeder in north-central British Columbia, much of the western part of the Yukon, interior Alaska and, near Inuvik in the Northwest Territories, the latter being the northernmost breeding range of the red-tailed hawk species. The race may breed as far south as northwestern Sonora in Mexico. Its eastern limits are reached around central Manitoba, while to the south the states of Montana, Wyoming, Utah, New Mexico and Colorado are mostly occupied by B. j. calurus.[9][10] Wintering birds from interior southwestern British Columbia may move south to as far as southwest to Guatemala and northern Nicaragua.[11] Linearly, this relatively large subspecies can seem to run almost contrary to Bergmann's rule, with birds of the Great Basin being longer winged than most Canadian ones.[12]

References

1. Sibley, David Allen (19 December 2009). "Subspecies names in the Sibley Guide to Birds". Sibley Guides: Identification of North American Birds and Trees. Random House. Archived from the original on 4 May 2014. Retrieved 4 May 2014. Website based on / supplement to book, Sibley, David Allen (11 March 2014). The Sibley Guide to Birds (Second ed.). Knopf Doubleday (Random House). ISBN 9780307957900.
2. Ferguson-Lees, J.; Christie, D. (2001). Raptors of the World. London: Christopher Helm. ISBN 978-0-7136-8026-3.
3. Palmer, R. S. ed. (1988). Handbook of North American Birds. Volume 5 Diurnal Raptors (Part 2).
4. Ridgway, R. & Friedmann, H. (1919). The Birds of North and Middle America: A Descriptive Catalogue of the Higher Groups, Genera, Species, and Subspecies of Birds Known to Occur in North America, from the Arctic Lands to the Isthmus of Panama, the West Indies and Other Islands of the Caribbean Sea, and the Galapagos Archipelago. Vol. 50, No. 8. Govt. Print.
5. Blake, E. R. (1977). Manual of Neotropical Birds (Vol. 1). University of Chicago Press.
6. Pearlstine, E. V. & Thompson, D. B. (2004). "Geographic variation in morphology of four species of migratory raptors". Journal of Raptor Research. 38: 334–342.CS1 maint: multiple names: authors list (link)
7. Steenhof, Karen & Kochert, Michael N. (1988). "Dietary Responses of Three Raptor Species to Changing Prey Densities in a Natural Environment". The Journal of Animal Ecology. 57 (1): 37–48. doi:10.2307/4761. JSTOR 4761.
8. Howell, Steve N. G.; Webb, Sophie (1995). A Guide to the Birds of Mexico and Northern Central America. Oxford University Press. ISBN 978-0-19-854012-0.
9. Preston, C. R. & Beane, R. D. (2009). "Red-tailed Hawk (Buteo jamaicensis)". The Birds of North America. doi:10.2173/bna.52.
10. Johnsgard, P. A. (1990). Hawks, Eagles, & Falcons of North America: Biology and Natural History. Smithsonian Institution.
11. Tesky, Julie L. "Buteo jamaicensis". United States Department of Agriculture. Retrieved 10 June 2007.
12. Fitzpatrick, B. M., & Dunk, J. R. (1999). "Ecogeographic variation in morphology of Red-tailed Hawks in western North America". Journal of Raptor Research. 33 (4): 305–312.CS1 maint: multiple names: authors list (link)