Buteo lineatus

ADULTS: A medium-sized, long-tailed, slender buteo, larger than the broad-winged hawk (BUTEO PLATYPTERUS) and smaller than the red-tailed hawk (BUTEO JAMAICENSIS). The long legs and feet are yellow, with less than half the tarsus feathered (versus half in red-tailed hawk). Wingtips do not reach the tail tip on perched birds. Sexes are similar, except that the female is larger, with considerable size overlap. In basic plumage the upperparts are dark but somewhat blotchy. The lesser upper wing coverts are rusty reddish or rufous and form the distinctive red-shoulder patch. The flight feathers are boldly barred with black and white above, not as boldly barred below, with a "window" (a white crescent-shaped panel) near the black outer primary tips. The underwing appears two-toned, with rufous coverts darker than the flight feathers. The wings are proportionately long and narrow, without the bulges of the red-tailed hawk. The leading edge is straight, while the trailing edge curves gently or not at all: "Seen from below, the wing of a red-shouldered hawk suggests a long, rectangular plank. The entire wing juts forward when the bird is in a full soar, as if it were reaching out, arms wide, to embrace something" (Dunne et al. 1988). Soaring typically occurs with wings in a slight downward droop. The underparts have transverse rusty to rufescent barring. The tail has several wide and very dark bars; the intervening narrow stripes and the tip of the tail are white. There is geographical and some sexual variation in the number of these tail bars (Palmer 1988, Clark and Wheeler 1987), among both adults and juveniles. The iris is dark brown and the cere is bright yellow.

YOUNG: nestlings are thickly covered with long, soft, silky down, longest on the head, yellowish-white above, tinged with "vinaceous-buff" on the back and wings, and whiter below. Somewhat older nestlings are covered with short, thick, woolly down, thickest and pure white on the belly, and grayish-white above. At about two weeks the wing quills sprout, followed by the scapulars, wing coverts, and contour plumage (Bent 1937, Kennard 1894).

Juvenile plumage is well-developed by fledging and held through the first winter into spring when gradually molted. It may not be completely molted until the following fall. The head is medium brown, usually with buffy superciliary line and dark brown malar stripes. The iris is light to medium gray-brown and the cere is greenish-yellow. The back is dark brown with some tawny mottling. The upper wing coverts are dark brown with some tawny and whitish mottling and often a hint of the red shoulder. Primaries are dark brown with a crescent-shaped tawny area on the upper surface next to the black tips. The white underparts are marked longitudinally with dark brown blobs. The underwing is uniform white to cream and shows the distinctive crescent panel or "window" when backlit. Leg feathers and undertail coverts are white and spotted with dark brown. The tail is brown above with many fine lighter brown bands.

A few albinistic and partially albinistic birds have been recorded (Clark and Wheeler 1987).

EGGS: smooth and slightly glossy. Ground color dull white or with a faint buff wash, overlaid with variable blotches, spots, or specks of reddish-brown or dark brown, and rarely pale lilac, with the larger markings concentrated toward the larger end.

VOCALIZATIONS: common during the breeding season (Bent 1937). The most common call is a "kee-aah," with the accent on first syllable, and second extended and with falling inflection (Palmer 1988). Another vocalization includes a single or repeated "kip," which the male gives when fetching prey and nearing the nest, and the female responds similarly, while nestlings have a chirping call. The blue jay (CYANOCITTA CRISTATA) is notorious for mimicking the cry of the red-shouldered hawk. Bent (1937) and Palmer (1988) noted a variety of other vocalizations attributed to this hawk, mostly variants of the kee-aah cry or the nest call.

BREEDING: varies from bottomland hardwoods and riparian areas (Stewart 1949, Henny et al. 1973, Bednarz and Dinsmore 1981, Kimmel and Fredrickson 1981, Woodrey 1986, Preston et al. 1989) to upland deciduous or mixed deciduous-conifer forest (Titus and Mosher 1981, Armstrong and Euler 1983, Morris and Lemon 1983, Crocoll and Parker 1989). Nesting areas are almost always found near some form of water, such as a swamp, marsh, river, or pond (Preston et al. 1989, Bosakowski et al. 1992), and the habitat is usually well forested (Portnoy and Dodge 1979, Kimmel and Fredrickson 1981, Titus and Mosher 1981, Morris and Lemon 1983, Ebbers 1989). Further, nesting habitat typically is mature forest with a well-developed high canopy and variable amounts of understory vegetation (Postupalsky 1980, Titus and Mosher 1981, Armstrong and Euler 1983, Morris and Lemon 1983, Titus 1984, Preston et al. 1989.). Sometimes occurs in coniferous stands in the West. In California, has been expanding range of occupied habitats to include various woodlands, including stands of eucalyptus trees amid urban sprawl (Ehrlich et al. 1992).

The nest is usually built in the main crotch of a large, living tree in mature forest, although in Florida, palmettos may be used. In eastern North America, nests generally are far from forest edges. At least 43 species of mainly deciduous trees have been chosen, so that the size and shape seem more important than the actual species (Bednarz 1979, Apfelbaum and Seelbach 1983, Titus and Mosher 1987, Palmer 1988, Ebbers 1989). The bulky structure of twigs, rather flat on top, is typically placed approximately halfway up the tree in the lower portion of the canopy (Morris et al. 1982, Titus and Mosher 1987). The typical height is between 11-15 m but can range from 1.5-33.5 m (Peck and James 1983, Ebbers 1989). The nest is lined with stems, leaves, lichen, and bark. Active nests are decorated with greenery and other materials. Hemlock and other conifer sprigs are often mentioned as nest greenery, as are deciduous sprigs once they have leafed out, and Bent (1937) mentioned such plants as flowering violets and nightshade. Other materials have included cornstalks, ears, and husks, dried tent caterpillar webs, tissue paper, twine, and nests of eastern wood-pewee, red-eyed vireo, and northern oriole (Palmer 1988).

In eastern North America, may use nest used previously by barred owl (STRIX VARIA) (and vice versa) (Palmer 1988). See Dijak et al. (1990) for information on nest-site characteristics affecting success and reuse of nests in Missouri.

NON-BREEDING: less restricted than that used for breeding; favors lowland areas near water, either standing or running, including river valleys, swamps, marshes, and perhaps canyon bottoms (Palmer 1988), and level, open country with scattered large trees (Bent 1937). In Florida, Bohall and Collopy (1984) found hawks most often in open areas such as pastures and fallow fields.

Mortality has been reported to occur during the incubation, nestling, and fledgling stages of the breeding season (Craighead and Craighead 1956, Janik and Mosher 1982, Bosakowski and Speiser 1986, Crocoll and Parker 1989). Adults and juveniles have also been reported to suffer mortality (McCrary and Bloom 1984, Crocoll and Parker 1989). Mortality has taken the form of wind-destroyed nests (Wiley 1975, Portnoy and Dodge 1979, Dijak et al. 1990), addled eggs (Janik and Mosher 1982, Crocoll and Parker 1989), starvation of nestlings (Crocoll and Parker 1989), human disturbance at or near the nest-site (Craighead and Craighead 1956, Wiley 1975), and predation of eggs, nestlings or adults (Craighead and Craighead 1956, Wiley 1975, Portnoy and Dodge 1979, Bosakowski and Speiser 1986, Crocoll and Parker 1989). The most frequent predators on eggs and young are raccoons (PROCYON LOTOR) and great horned owls (BUBO VIRGINIANUS).

Breeding density is highly variable; recorded values include one pair per 48.7 ha in central Maryland (Stewart 1949), one pair per 171 ha in western New York (Crocoll and Parker 1989), one pair per 417 ha in Massachusetts, one pair per 455-588 ha in Indiana, one pair per 645 ha in Michigan (Craighead and Craighead 1956), and 1 pair/1000 ha in Wisconsin (see Peterson and Crocoll 1992). Stewart (1949) found nests a mean distance of 1072 m apart in the wide upper Patuxent River drainage in Maryland, and Parker (1986) found similar internest distances in Missouri. Crocoll and Parker (1989) found nests a mean distance of 1271 m apart in the Canadaway Creek Wildlife Management Area of western New York. Adjacent nests were 0.37-1.27 km apart in creek bottoms in southern California. Breeding home range of radio-tagged birds in California averaged 62 ha for males, 37 ha for females; used less space when not breeding. In northern New Jersey, nesting density was 0.22 nests per 100 ha, the highest density yet reported (about twice that reported in the few comparable studies in other states) (Bosakowski et al. 1992).

Often uses nests of previous years (Terres 1980). Nesting territories can be used for many years by a succession of pairs, even in the face of logging and (formerly) egg collecting. Bent (1937) reported an unbroken record of 26 years for a territory that was occupied for at least 42 years, until the woods were nearly ruined by cutting. His longest record was 47 years, but he knew of a tract that was occupied for over a half-century, from 1872 until 1923.

LEUCOCYTOZOA sp., a hematozoan, was detected in the blood of hawks tested in Oklahoma (Kocan et al. 1977). Two lice (COLPOCEPHALUM FLAVESCENS and PHILOPTERUS TAUROCEPHALUS) and one bird fly (LYNCHIA AMERICANA) have been found on red-shoulders (Peters 1936). In New York, the ears of nestlings commonly were full of maggots (PROTOCALLIPHORA SPLENDIDA) (Sargent 1938). These maggot infestations seemingly did not cause deafness or hinder survival (Hands et al. 1989).

Courtship, territory establishment, and nest building (or refurbishing) occur shortly after arrival on the breeding grounds. In New York, Crocoll and Parker (1989) recorded birds back on territories and relining nests during the second and third weeks of March. Portnoy and Dodge (1979) in Massachusetts observed courtship flights during March and nest relining during the last week of March and first week of April. Morris et al. (1982) in southwestern Quebec observed territorial hawks soaring from early March to mid-April. Farther south, nesting activities begin several weeks earlier. Records from Alabama, Louisiana, and Oklahoma indicate that breeding begins in February.

Aerial nuptial displays are impressive and include "high-circling" and "sky-dancing," both extremely vocal performances. In the sky-dance, one individual (presumably the male) rides an upward thermal, crying as it circles, then drops with folded wings into a steep dive, pulling up and then shooting upward again. Neighboring pairs often join in, with as many as ten birds involved. The sky-dance can be immediately followed by copulation, which "occurs repeatedly and over considerable time" (Palmer 1988).

Clutch size varies from one to six (Palmer 1988), with two to four eggs being the most common sizes throughout the range. Clutch size is commonly two in Florida, three to four in the northern U.S. A mean of 3.45 eggs from 42 clutches was reported for the Great Lakes States (Henny 1972). Eggs are laid January-June (mostly March-April) in the southeastern U.S., March-June (mostly April) in northern U.S., mostly March-April in California (Palmer 1988). Nests late March to late May in Maryland (Bushman and Therres 1988) and New York (Bull 1974).

Incubation is by both sexes, but mainly by the female, who is fed by the male, and commences with the laying of the first egg. The incubation period is around 33 days per egg (Newton 1979), and the young hatch asynchronously and thus vary in size, as with many raptors (Newton 1979). The semi-altricial young are inactive at first, becoming active at about 10 days. Feathering begins in about two weeks. The nestling period lasts from five to six weeks (Harrison 1978, Crocoll and Parker 1989). Young leave the nest at 5-6 weeks; in California, first flight occurs at about 45 days (sometimes at considerably older age). Fledging generally occurs in mid-June in Maryland (Janik and Mosher 1982), June to mid-July in New York (Bull 1974, Crocoll and Parker 1989), and late June-early July in Massachusetts (Portnoy and Dodge 1979). Dates are similar throughout the northern range of the species, and are advanced 4 to 8 weeks in the south. In southern California, parents supplied food to young for 8-10 weeks after fledging.

Although a few nest at one year of age (Apanius 1977), most first breed when at least two years old (Palmer 1988). There has been evidence of polyandry with copulation and trio bonding at the nest recorded (Palmer 1988).

Nesting success (measured as the percentage of nests that fledge at least one young) has been reported to vary from 52.9% in Maryland to 100% in Missouri with an average of 68.7% over nine North American studies (Crocoll and Parker 1989). Two one-year studies reported lower nest success rates: 47.4% for 19 nests in northern Lower Michigan in 1986 (Ebbers 1986), and 25% for 1966 at the Patuxent Wildlife Research Center, Maryland (Henny et al. 1973).

The average number of young fledged per nest over the previously cited nine studies varied from 1.11 young to 2.9. Henny et al. (1973) used a mathematical model and field data to predict that in a stable population each pair should fledge an average of 1.95 young. Four of the nine above mentioned studies had fledging numbers below the Henny et al. (1973) standard. Three of the studies were conducted in the Northeast: New York (1.11 young fledged, Crocoll and Parker 1989), Western Maryland (1.8 young fledged, Janik and Mosher 1982), and central Maryland (1.58 young fledged, Henny et al. 1973). One Michigan population produced a mean 1.2 young fledged (n = 44) over three years of study, while another population fledged 2.2 young (n = 29) over the same time period (Ebbers 1989). Ebbers (1989) noted that there is concern that the 1.95 standard may be too high because of possible biases in the data used to scale the model values. Nevertheless, it does appear that some populations produce excess young ("source" populations), while others would not survive without immigration ("sink" populations).