SPECIES

Red-tailed Hawk Buteo jamaicensis Scientific name definitions

C. R. Preston and R. D. Beane
Version: 1.0 — Published March 4, 2020
Text last updated May 20, 2009

Demography and Populations

Measures of Breeding Activity

Age At First Breeding; Non-breeders

Average age at first breeding is not known, but few juveniles (< 2 yr; possessing brown tail) of either sex observed to breed (Henny and Wight 1972, Wiley 1975a). A variable percentage of resident birds fail to breed in a given year. Frequencies of nonbreeding resident pairs reported as 10% in Wisconsin (Orians and Kuhlman 1956), 16% in Michigan and Wyoming (Craighead et al. 1969), 26% in New York (Hagar 1957), and 14% in Alberta (Luttich et al. 1971). Why some paired birds fail to breed remain unclear.

Clutch

Henny and Wight (Henny and Wight 1972) analyzed clutch size data from the conterminous U.S. and s. Canada collected between 1870 and 1968 (Appendix 1). Clutch sizes increased from south to north and from east to west. The smallest mean clutch size was from Florida (2.11, n = 9), and the largest was from Oregon and Washington (2.96, n = 26). In central Alberta, the number of eggs and young nestlings in 68 nests averaged 2.1 (Luttich et al. 1971), which is lower than any of the mean clutch sizes reported by Henny and Wight (Henny and Wight 1972). Mean clutch size for 27 nests in Alaska was 1.96 during years when snowshoe hares were scarce (Lowe 1978). Geographic and temporal variations in clutch size may be adjusted to food availability, but this has not been demonstrated conclusively.

Annual And Lifetime Reproductive Output

Mean number of fledglings/pair/yr was 0.91 (n = 22) in Michigan (Craighead et al. 1969), 1.36 (n = 137) in Montana (Johnson 1975d), and 1.40 (n = 15) in the Appalachians (Janik and Mosher 1982). In Wisconsin, means of 1.8 (n = 27), 1.1 (n = 33), and 1.4 (n = 27) young/nest were fledged in successive years (Orians and Kuhlman 1956). Most estimates of nest success range from 58% (Hagar 1957) to 93% (Mader 1978) in a given year. Mader (Mader 1982) summarized data from several studies and reported average nest success 83% (n = 309), average hatching success 84% (n = 379), and average nestling success 73% (n = 152) (“nest success” = % nests fledging ≥1 young; hatching success” = % eggs laid that produced hatchlings; “nestling success” = % nestlings hatched that fledged.

Reproductive success varies with prey abundance, perch density and distribution, and proximity of nests to congeners. In Oregon, reproductive success varied markedly among territories in relation to dispersion and density of perches used as foraging sites and secondarily to the abundance of ground squirrels (Janes Janes 1984b, Janes 1984a). In Washington State, sibling aggression and brood reduction occurred, apparently in response to bad weather limiting parental hunting success (Stinson Stinson 1980b). In the Canadian prairie-parkland ecotone, reproductive success decreased with decreasing distance to nests of congeners (Schmutz et al. 1980). In Oregon, brooding Red-tails suffered a lower rate of nest success when nests of congeners were visible, even though there was no correlation between reproductive success and distance to nests of congeners (Coues 1874a). In Puerto Rico, nest success (Mayfield 1961a, Johnson 1979) was 43% in lowland pastures and 34% in rain and cloud forests, and mean number of fledglings was significantly higher in lowlands (1.5, n = 11) than in upland forests 0.7, n = 14) (Santana and Temple 1988).

No information available on lifetime breeding success.

Life Span and Survivorship

Bird Banding Laboratory records summarized in 1994 showed that of 5,194 Red-tails banded and recovered, only 31 survived ≥ 17 yr and 11 survived ≥20 yr (Soucy 1995). Long-lived, free-ranging Red-tails include 2 birds aged 22 yr, 7 mo., 1 bird 23 yr, 5 mo (Klimkiewicz and Futcher 1989). The longevity record for a free-ranging Red-tail is 25 yr, 9 mo. (Frock 1998). A captive female Red-tail lived at least 29.5 yr (Palmer 1988f).

Disease and Body Parasites

Disease

Bacterial infections include peritonitis, myocarditis, granulamotous, sarcocystosis, airsacculities, mycobateriosis (Michigan Department of Natural Resources 2008, Tell et al. 2004). Synovial chondromatosis was found in a Red-tail in the northern prairie states (Stone et al. 1999a), and pansteatitis lead to the death of a juvenile female Red-tail in Quebec, Canada in 1998 Wong et al. 1999).

Red-tailed Hawks also host and are susceptible to West Nile virus (Center for Disease Control 2007), aspergillosis, and avian malaria (Nayar et al. 1998). West Nile virus can cause chronic fatal disease in Red-tailed Hawks; transmission routes are uncertain, but mosquito bites and ingestion of infested prey are the most likely vectors (Wünschmann et al. 2004).

Body Parasites

In Wyoming, blackflies (Simulium canonicolum) caused mortality in 14% of nests where young hatched, through a combination of physical harassment, transmission of disease, and direct loss of blood and body fluids from biting flies (Smith et al. 1998b). Nestling parasitism by the blood-sucking fly, Eusimulium clarum, has been documented during wet years in California (Fitch et al. 1946b). Myiasis, an infection caused by larvae of the blood-sucking fly genus Protocalliphora, was common in nestlings studied in Wisconsin (Petersen 1979a) and s.-central Montana (Seidensticker and Reynolds 1971). Other external parasites include Craspedorrhynchus americanus, Degeeriella fulva, Colpocephalum flavescens, Legeeriella fusca, sarcoystosis, and Philopterus taurochalus (Peters 1936, Pfaffenberger and Rosero 1984, Michigan Department of Natural Resources 2008). Known protozoan blood parasites include Haemoproteus, Leucocytozoon, and Hepatozoon (Stabler and Holt 1965).

Causes of Mortality

Most deaths attributed to predation and human-related causes (but see Disease, above). In Alberta, predation by Great Horned Owls was cited as the chief cause of nestling deaths (Luttich et al. 1971). Starvation/fratricide (5 of 13 deaths) and falling from the nest (4 of 13 deaths) were considered the primary causes of nestling mortality in Wisconsin; human interference (not by investigator) was blamed for 2 of 13 nestling deaths in this study (Petersen 1979a). Of 16 egg/nestling losses in s.-central Montana, 7 were attributed to human interference (at least one involving investigators), 4 to Great Horned Owls, 2 to unspecified disease, 2 to wind, and one to American Crows (Corvus brachyrhynchos) (Seidensticker and Reynolds 1971). In Orange County, CA most nest failures were attributed to human interference (Wiley 1975a). Leading causes of yearling and adult mortality include shooting, trapping, electrocution, and collisions with structures, automobiles, and aircraft. (Keran 1981, Michigan Department of Natural Resources 2008, Hoover and Morrison 2005). See also Conservation and Management.

Population Spatial Metrics

Natal dispersal

In North America, fledglings may remain in the parental territory for 18–70 d after leaving the nest (Johnson 1973d, Petersen 1979a). Single fledglings may take more time to develop flying and hunting skills, and thus disperse later than fledglings from broods of >1 young (Petersen 1979a). Pre-migration dispersal includes northerly or lateral movements in all but northernmost populations (Luttich et al. 1971). Five of 6 Red-tails banded as nestlings in Wisconsin were recovered within the hatching year, 4 at least 100 km (maximum 3,000 km) south of the natal territory, and one 184 km to the northeast. A sixth recovery was reported within 10 km of the natal territory 44 mo after the bird was banded as a nestling (Petersen 1979a). In Puerto Rico, fledglings remained in natal territory as long as 141 d after fledging (Santana and Temple 1988).

Fidelity to breeding site and winter home range

Red-tails exhibit a high degree of territory fidelity, at least among females (Janes 1984a). Sedentary individuals typically remain in or near the breeding territory throughout the year (Petersen 1979a). Little is known about fidelity to winter home range by migratory individuals. At least in the s. and midwestern U.S., local abundance of Red-tails fluctuates greatly with changes in weather during winter, indicating nomadism by some individuals (CRP).

Home range

Size of home range varies with topography, habitat structure, food availability, human disturbance and season; e.g., typically varies inversely with the amount of unbroken woodland (Fitch et al. 1946b, Austing 1964, Petersen 1979a). Petersen (Petersen 1979a) conducted a year-round study of a largely sedentary population in Wisconsin, and determined mean home range size in each season: fall male 390 ha, n = 1, female 123 ha (60–185), n = 2; winter male 157 ha (150–160), n = 3, female 167 ha (72–344), n = 6; spring male 163 ha (147–179), n = 2, female 85 ha (31–144), n = 6; summer male 117 ha, n = 1, female 117 ha (44–206), n = 5.

Population Status

Numbers/Density

Global population estimates vary widely, from 100,000 to 1,000,000 individuals (Ferguson-Lees and Christie 2005), to more than 2,000,000 individuals (Farmer et al. 2008a). An estimated 1,960,000 nesting Red-tailed Hawks, or nearly 90% of the global population, according to one estimate, reside in North America (Farmer et al. 2008a).

Population densities are usually estimated using a variety of roadside, foot, and aerial surveys (Fuller and Mosher 1981). Reported estimates of breeding densities vary from 1.3 to 50 km2/pair and show no clear geographic trend (Appendix 2). Highest breeding densities in North America reported in mixed wooded and open environments in California: 1.3 km2/pair (Fitch et al. 1946b) and Colorado: 2.0 km2/pair (McGovern and McNurney 1986).

In contrast to North American continental populations, breeding density was highest (1.56 km2 /pair) in closed-canopy, mountainous forest, and lowest (5.33 km2/pair) in open-country lowlands in Puerto Rico (Snyder et al. 1987c, Santana and Temple 1988, Snyder and Snyder 1991). Lowest breeding densities overall reported from suboptimal habitat in Ohio: 50 km2/pair (Shelton 1971), 43 km2/pair (Misztal 1974) and near Fairbanks, AK 46.6 km2/pair (Lowe 1978). Variation in nesting density within and between geographic regions is best explained as a response to local landscape composition and prey availability. Highest breeding densities expected to occur in prey-rich areas, with abundant and optimally-spaced hunting perches, where other diurnal raptors do not provide significant interference (Palmer 1988f).

Similarly, local winter densities are greatest where snow cover is minimal and perch and prey availability are high (Robbins et al. 1986a, Root 1988b). Peak early winter densities in the United States are in fertile regions of California, from Kerns National Wildlife Refuge north to Clear Lake, w. Nevada, and in the agricultural strongholds in e. Oklahoma, n. Missouri, and s. Iowa; peak in the central U.S. is roughly bordered by the Appalachians to the east, winter temperatures below –12°C to the north, and arid conditions (< 61 cm annual precipitation) to the west (Root 1988b).

Peak early winter abundances of overwintering harlani occur in ne. Arkansas, central Oklahoma, and central Missouri (Root 1988b). Especially high local densities may occur around poultry dumps or other ready sources of food (Preston 2000). During a 3–yr period in nw. Arkansas, peak winter densities occurred in Jan and varied from 5.2 hawks/km2 to 6.4 hawks/km2 (x = 5.9) (CRP). In central Arkansas, peak winter densities also occurred in Jan and varied from 2.4 hawks/km2 to 3.8 hawks/km2 (mean = 4.3) during a 5–yr period (CRP). Most of these birds were nonresidents. In Wisconsin, where most over-wintering birds are presumably residents, average winter densities of 1.19/km2 (Orians and Kuhlman 1956), 1.96/km2 (Kabat and Thompson 1963), and 1.14–2.40 km2 (Gates 1972) have been reported. In s.-central Ohio, mean density was 0.17/km2 over 4 yr (Bildstein 1987a).

Trends

Few data, but populations appear to be stable (Ferguson-Lees and Christie 2005, Farmer et al. 2008a, NatureServe 2008). Summary analyses of data from Breeding Bird Surveys (BBSs) indicate that Red-tail breeding populations showed statistically significant (p 0.01) increasing trends of 2.9%/yr, 2.2%/yr, and 1.7%/yr across eastern, central, and western BBS regions, respectively, from 1966 – 2007, although regional credibility measures are weaker in eastern and central regions than in the western region owing to relatively low abundance or detectability (Sauer et al. 2008a).

During this overarching time period, only the state of Florida and provinces of Manitoba and Nova Scotia showed declines, and none were statistically significant (p 0.05). Within the time period, Illinois, Iowa, and Manitoba showed statistically significant declines (-9.0%/yr, -7.8%/yr, -13.0%/yr, respectively) in breeding Red-tail numbers from 1966-1979, but Illinois and Iowa showed increasing trends of 6.8%/yr and 4.5%/yr, respectively, from 1980 to 2007, and the trend in Illinois is statistically significant (p 0.01). The declining trend (-0.8%/yr) from 1980 to 2007 in Manitoba is not statistically significant. Data from U.S. Christmas Bird Counts (CBCs) generally parallel those of BBSs, showing a nationwide increasing trend of Red-tails counted during the last 4 decades (National Audubon Society 2002b).

Trends from fall raptor migration counts in e. North America from 1974 to 2004 show a statistically significant (p 0.01) increase of 3.1%/yr recorded at Lighthouse Point, CT, and a statistically significant decrease of -1.9%/yr recorded at Hawk Mountain Sanctuary, PA (Farmer et al. 2008a). Trends from all other counts were not significantly different from zero. From 1994 to 2004, statistically significant increases in migrating Red-tail numbers were recorded at Lighthouse Point (3.1%/yr, p 0.05), and statistically significant decreases were recorded at Cape May Point (-9.8%/yr, p 0.05) and Hawk Mountain Sanctuary (-1.8%/yr, p 0.01) (Farmer et al. 2008a).

Data from raptor migration counts in western North America indicate increasing trends in Red-tails counted from 1985 to 2005 at the Manzano Mountains, NM (2.1%/yr, p 0.05) and from 1983 to 2005 in the Goshute Mountains, NV (2.0%/yr, p 0.05), with no other locations recording statistically significant trends. Manzano Mountains (2.1%/yr, p 0.05), Goshute Mountains (2.0%, p 0.05), and Boise Ridge, ID (7.3%/yr, p 0.01) recorded statistically significant increasing trends in numbers of migrating Red-tails from 1995 to 2005, while Lipan Point, AZ recorded a statistically significant decrease (-10.7/yr, p 0.01) during the same period (Farmer et al. 2008a).

Taken together the BBSs, CBCs and raptor migration counts in western North America suggest possible shifts in migration patterns related to drought or other factors, and a regional population or range expansion at least in the southern Rockies (Farmer et al. 2008a).

Population Regulation

Few data; little studied. Nest sites and food supply are two factors likely to limit Red-tail populations, although nest parasites, disease, and pesticides hold the potential to exert a significant effect locally. The relative importance of these factors varies with location and year.

Although Red-tails use a variety of nesting substrates (see Breeding: nest site), they typically require an elevated site with unobstructed access near large, open hunting areas. Populations may be limited by a scarcity of appropriate sites in some regions (e.g., prairie/parkland ecotone), despite high prey availability. In central Alberta, local breeding population size, breeding rate, and nest spacing of Red-tails remained remarkably constant during a 7–yr period, despite large yearly fluctuations of several prey species (Mcinvaille and Keith 1974). Intense territoriality related to nest site availability may have both spaced and limited this population. Productivity is reduced in some regions where a paucity of nest sites forces Red-tails to nest near congeners. Where Red-tails nested close to Swainson's and Ferruginous hawks in Alberta and Oregon, Red-tail reproductive success declined markedly, apparently independent of food supply (Schmutz et al. 1980, Coues 1874a).

Where appropriate nesting sites are abundant yet unoccupied, populations are presumably limited primarily by prey density. For example, in saguaro-palo verde flatland, nesting Red-tails used only about 0.2% of total nesting platforms (tall saguaro with at least two supporting branches) available for nesting in a particular year (Mader 1978). Rather than prey density per se, distribution and abundance of suitable perches influence productivity in some areas by directly affecting hunting efficiency (Janes 1984b, Janes 1984a).

Predation and interference by Great Horned Owls may depress Red-tail populations where nest sites or food are scarce and there is temporal overlap in breeding cycles. For example, yearly predation-disappearance rate among young Red-tails in Alberta was directly related to an increase in nesting pairs of Great Horned Owls (Luttich et al. 1971).

Weather patterns may exert a strong local influence on annual reproductive output. Prolonged cloudy and rainy periods during the nestling period in Puerto Rico drastically reduced feeding bouts and presumably productivity (Santana and Temple 1988).

Recommended Citation

Preston, C. R. and R. D. Beane (2020). Red-tailed Hawk (Buteo jamaicensis), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.rethaw.01