Gray Hawk Buteo Nitidus

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Library of Congress Cataloging-in-Publication Data

The raptors of Arizona / edited by Richard L. Glinski; with full-color illustrations by Richard Sloan. p. cm. Includes bibliographical references and index. ISBN 0-8165-1322-8 (cloth : acid-free paper) 1. Birds of prey—Arizona. I. Glinski, Richard L., 1950 - II. Arizona. Game and Fish Dept. QL696.F3R375 1998 598.9'09791—dc21 97-21055 CIP

British Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

For information on obtaining signed and numbered reproductions of the paintings created for this book, contact the Arizona Wildlife Foundation at 1-800- 827-WILD. Each image is the same size as the original: 13.5" x 18". These reproductions can be purchased as artist's proof sets with all 42 prints, sets of all 42 prints, sets of 10 prints, or single prints.

All proceeds to benefit the educational programs of the Foundation. Gray Hawk Buteo nitidus

Richard L. Glinski

DESCRIPTION. Translated from the Latin, Buteo along the sides of the throat. In both adults and ju- nitidus means "shining hawk" or "star buzzard." veniles the bill is dark gray or black, the cere and This striking medium-sized hawk is about 14 -18 exposed legs and toes are yellow, and the iris is inches long, has a wingspan of 32-38 inches, and brown. The juvenal plumage is replaced by adult weighs 13-23 ounces (Wheeler and Clark 1995). plumage during the second year. The male is smaller than the female. In its propor- Gray Hawks are perhaps the most vocal raptors tions the Gray Hawk resembles an accipiter more in Arizona, and usually it is their voice that reveals than a buteo, with relatively shorter wings, longer their presence. I have identified two basic calls: the tail, and longer and thinner tarsi and toes than typi- three-note territorial peacock call and the one-note cal buteos. Its alternating flapping and gliding flight irritation call. The latter call has variations that in- is also accipiter-like. The Gray Hawk's resem- . clude a one- or two-note whine. The peacock call is blance to the Northern Goshawk doubtless is the given to proclaim territorial boundaries. It varies reason for its other name, "Mexican Goshawk," a from a regular to a rolled, slurred, and exaggerated misnomer that confused some early ornithologists. three-note call, depending on the intensity of the N. K. Johnson and Peeters (1963) placed the Gray territorial encounter. For nest defense, Gray Hawks Hawk along with the Red-shouldered Hawk and blurt an irritated, trailing one-note call. In situa- Broad-winged Hawk in a group they termed wood- tions of greater stress, as during an aggressive ter- land buteos. The members of this group share ac- ritorial encounter with another Gray Hawk or nest cipiter-like adaptations for maneuvering in forests defense against another raptor, the whine is often and woodlands. Millsap (1986) agreed with this followed quickly by a three-note territorial call. assessment and, based on measurements and The whine is also heard during copulation and plumages, recommended that the Gray Hawk be food exchanges between adults. A squeal, consist- placed in a separate genus (Asturina) and that the ing of a series of slurred three-note calls given rap- Gray Hawks in the United States and northern Mex- idly, is given during extreme agitation, as during ico be distinguished as a separate subspecies. food exchanges between the male and female at the The adult Gray Hawk has a slate gray back, nest. The female gives the squeals, which resemble white-fringed upper tail coverts, and a black tail the intensive begging calls of older nestlings. The with two or three white bands. The breast, abdo- male's voice is generally higher pitched than the fe- men, and thighs are finely barred gray and white, male's, and the juvenile's voice is raspy and broken. and the undertail coverts are white (plate 14). The The Gray Hawk's erect posture and long, verti- juvenal plumage is typically hawklike, dark brown cally hanging tail are good identification charac- on the back and buff streaked with brown on the ters, but the best field mark for adults is the bold front. The tail is brownish gray with five to nine black-and-white tail contrasting with the slate gray dark bands. The sides of the face are lighter in color back. This color pattern combined with the accipi- than the crown and neck, and there is usually a dis- ter-like flight, distinctive voice, and limited range tinctive dark stripe running from the base of the bill make the Gray Hawk easy to identify in the field.

82 Gray Hawk 8 3

DISTRIBUTION. The Gray Hawk occurs from the Amazon Basin through Central America into the southwestern United States. Some of the early Ari- zona and New Mexico records are dubious because the name "Mexican Goshawk" caused confusion among early ornithologists, who knew the accipiter goshawk and assumed that this same bird near the Mexican border was the "Mexican Goshawk." For example, Law (1929) claimed to have seen Gray Hawks in the Chiricahua Mountains, but Hub- bard's (1972) scrutiny of this record revealed that Law had seen a Northern Goshawk. The historical distribution in Arizona was the Santa Cruz River basin, particularly the major tributaries near what now is Tucson (Bendire 1892; Swarth 1905; Bent 1937; Brandt 1951; Phillips et al. 1964; Stensrude 1965). More recently, the San Pedro River has become home to nearly one-third of the Arizona population. Breeding observations outside 0 25 50 75 100 these two drainages include at least one nest on the MILES

San Bernardino National Wildlife Refuge known Gray Hawk distribution in Arizona since the mid-1980s (pers. observ.) and sightings along the Verde River at Dead Horse State Park in Yavapai County, where C. Tomoff (pers. comm.) saw an adult and yearling separately on four dif- south of Wickenburg on 16 September 1980 (C. To- ferent occasions from 16 June through 3 July moff pers. comm.), 18 July 1993 (S. Miller pers. 1992. C. Stensrude (pers. comm.) reported a nest in comm.), and 12 May 1996 (C. Babbitt [fide J. Witz- 1963 from along Seven Springs Wash in Maricopa eman]); a single adult along the lower Verde on 13 County. Pember's (1892) record of a Gray Hawk April 1975 (Monson and Phillips 1981); and an nest with three eggs found on 16 April 1892 was adult at the Salt River in Tempe on 24 April 1993 discarded by Phillips et al. (1964). However, Ed- (D. Hews and B. Terkanian [fide J. Witzeman]). gar A. Mearns's journal records a single Gray Hawk The best place to observe Gray Hawks now is from the Gila River between Maricopa and Sacaton along Sonoita Creek at the Nature Conservancy's on 12 May 1885, which when combined with more Patagonia-Sonoita Creek Sanctuary. Be on the mes- recent northerly records sustains the possibility of quite and grassland hillsides bordering the cotton- historical occurrence along the Gila River. J. Witze- wood forest of Sonoita Creek about midmorning in man (pers. comm.) observed lone Gray Hawks April, and you will have a streamside seat to one along the lower Santa Cruz River at the Marana pe- of the most vocally demonstrative raptors in North can grove from late August into October in 1991, America in the midst of nest building and court- 1992, 1994, and 1995, suggesting nesting areas to ship. You can follow the birds through the canopy the north. by their sounds, only guessing what all the noise Additional observations of Gray Hawks away means, and get good looks as one or both break into from the Santa Cruz and San Pedro drainages in- the sky above the trees. And best of all, you will not clude lone adults along the Hassayampa River be an intruder. 84 RICHARD L. GLINSKI

HABITAT. Gray Hawks typically inhabit arid de- the nest picking intently at leafy green sprigs. Cot- ciduous forests and woodlands throughout their tonwood is the favored nest tree, but I have seen range. In the tropics, they prefer xeric second- nests in ash, willow, and oak as well. Early or- growth and thorn forests. In Arizona, at the temper- nithologists described nests in mesquite (Swarth ate northern extreme of their range, Gray Hawks 1905) and hackberry (Brandt 1951). Nests are usu- occur mostly in strands of Sonoran Riparian De- ally placed in the upper third of the canopy and are ciduous Forest and Woodlands and to a lesser ex- constructed of leafy green twigs from the nest tree tent in Madrean Evergreen Woodland along the Ari- or nearby trees that the birds break off with their zona-Sonora border (vegetation classification after bills. D. E. Brown 1982) amid the diverse herpetofauna Egg laying usually occurs during the first part of of southern Arizona (Gloyd 1937) that constitutes May. Incubation, which is performed only by the fe- their major food. male, lasts about 33 days. I investigated 119 breed- Bank cutting, the result of erosion from drought ing attempts from 1973 through 1977 and found an and torrential rainfall in the late 1800s (Bryan average of 2.6 eggs per clutch and 1.2 young per 1925), may have increased Gray Hawk habitat in occupied breeding site. B. Bibles (pers. comm.) some areas, such as along the San Pedro River. checked productivity of 25 nesting sites along the Stream flows cut up to 20 feet into the alluvium, San Pedro River and documented a mean of 1.1 and now ribbons of cottonwoods occur between young per occupied site in 1995. The hawklets re- the bank walls, on which grow woodlands of mes- main in the nest for approximately six weeks and quite and hackberry. Such areas afford good condi- become self-sufficient after an unknown period. tions for whiptail lizards, species that characteris- Raptors that I have found nesting within a mile tically exploit new areas born from catastrophic of breeding Gray Hawks include the Zone-tailed habitat alteration (Wright and Lowe 1968; Gerrit- Hawk, Common Black-Hawk, White-tailed Kite,' sen 1980; Serena 1980). Mississippi Kite, Cooper's Hawk, Red-tailed Hawk, The San Pedro River above Fairbank, and es- Harris' Hawk, and Swainson's Hawk. pecially at the elevations above Hereford, is only The Gray Hawk feeds mainly on reptiles (Ama- marginally suited for the development of mesquite don and Phillips 1939; West 1975; Glinski and Mill- forests. The higher elevation there permits cata- sap 1987). Lizards constituted 74 percent of the strophic freezes, which can kill mesquite or pre- prey that I observed delivered to nestlings in Ari- vent it from growing larger than a shrub (Glinski zona. Other prey items included garter snakes (5 and Brown 1982). However, the present attraction percent), nestling and adult birds (11 percent), and for the Gray Hawk is the dry erosion benches, the mammals (10 percent) (Glinski 1988). Their speed hunting perches of dead standing mesquite, and the and maneuverability enable Gray Hawks to capture whiptails that thrive there. both arboreal and terrestrial lizards, which they spot from low perches in dense woods. LIFE HISTORY. Gray Hawks arrive in Arizona The winter haunts of Gray Hawks include Ari- about mid-March, and the adults usually return to zona only on rare occasions. Such an occasion was the previous year's nesting sites. Courtship, which on 15 December 1978, at Dudleyville, Arizona, the features the three-note peacock call, undulating northernmost regularly occupied breeding area flights by the male, and nest building, begins im- known for the species. I had just crawled out of mediately. Both pair members construct the nest, a frosted sleeping bag and mimicked a territorial but the male performs most of the early work. The three-note call, more to elicit the feeling of spring female builds most of the bowl, sitting for hours in than to detect Gray Hawks. To my surprise, a pair Gray Hawk 8 5

of adult Gray Hawks bolted from the forest of dor- however, sightings have increased in Texas along mant cottonwoods, calling and displaying with all the Rio Grande from the Big Bend to Brownsville, the zest of April territoriality. where as many as six pairs regularly nest. Gray Hawks have expanded their range in Arizona, too, S TAT U S . The Gray Hawk does not have special fed- but the most important habitats are still in the eral protection under the Endangered Species Act watersheds of the Santa Cruz and San Pedro Rivers (16 u.s.c. 1531 et seq.). In Arizona, the stronghold (see distribution map). for this species in the United State"s, about 80 Gray In 1965, no Gray Hawk nesting areas were for- Hawk breeding areas are presently known. The mally protected, but by 1975 the Arizona Nature nesting sites appear to be regularly occupied, and Conservancy and responsible landowners along reproductive output seems adequate to meet the Sonoita Creek had secured the future of about 12 present mortality rate. Because Gray Hawks that nesting sites. The acquisition of 36 miles of the San fledge from nests in Arizona winter in Mexico, Pedro River by the U.S. Bureau of Land Manage- however, the health of the state's population may be ment in 1987 protected another 25 occupied nesting tied to conservation efforts there. territories (Rosenkrance 1988). About eight Gray Seven Gray Hawks that I banded as nestlings in Hawk breeding sites were protected when breeding Arizona were recovered in northern Sinaloa. In habitat along Arivaca Creek was acquired by the that area of Mexico, the native thornscrub habitat U.S. Fish and Wildlife Service for incorporation that Gray Hawks prefer is being cleared for agricul- into Buenos Aires National Wildlife Refuge. Re- ture, and the living fencerows common to Mexican sponsible stewardship by private landowners has agriculture (Nabhan and Sheridan 1977) afford re- been assisted by legislation that affords tax in- fugia of sorts amid massive habitat destruction. centives for establishing "conservation easements." Since reptiles, the major food of Arizona's Gray Thus, the majority of the nearly 80 regularly occu- Hawks, are not migratory, we would not expect pied nesting sites of Gray Hawks known in Arizona them to exhibit chemical contamination in the will likely survive the wave of human settlement form of DDT or other pesticides. Five eggs I col- that is predicted to hit the state in the near future. lected from Arizona nests in the 1970s were of Responsible land management came just in the nearly identical thickness (0.341 mm average) as nick of time. In the last 25 years, vast areas of mes- 19 Arizona eggs collected from 1898 to 1930. quite have been cleared for alfalfa pastures. Only Arizona sustained nearly all the known breed- by preserving Arizona's mesquite bosques can we ing populations of this hawk in the United States prevent extirpation of this raptor from the United during the mid-1980s (Glinski 1988). Since then, States.