Circus cyaneus - (Linnaeus, 1766)
Northern Harrier
Other English Common Names: Marsh Hawk, northern harrier
Taxonomic Status: Accepted
Related ITIS Name(s): Circus cyaneus (Linnaeus, 1766) (TSN 175430)
French Common Names: busard Saint-Martin
Spanish Common Names: Gavilán Rastrero
Unique Identifier: ELEMENT_GLOBAL.2.1009485
Element Code: ABNKC11020
Informal Taxonomy: Animals, Vertebrates - Birds - Other Birds
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Aves Accipitriformes Accipitridae Circus
Genus Size: C - Small genus (6-20 species)
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Concept Reference
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Concept Reference: American Ornithologists' Union (AOU). Chesser, R.T., K.J. Burns, C. Cicero, J.L. Dunn, A.W. Kratter, I.J. Lovette, P.C. Rasmussen, J.V. Remsen, Jr., J.D. Rising, D.F. Stotz, and K. Winker. 2017. Fifty-eighth Supplement to the American Ornithologists' Union Check-list of North American Birds. The Auk 134:751-773.
Concept Reference Code: A17AOU01EHUS
Name Used in Concept Reference: Circus cyaneus
Taxonomic Comments: Circus hudsonius was formerly considered conspecific with C. cyaneus Linnaeus, 1766 [Hen Harrier], but treated as separate on the basis of differences in morphology, plumage, and breeding habitat (Grant 1983, Thorpe 1988, Dobson and Clarke 2011, Etherington and Mobley 2016) commensurate with differences between other recognized species of Circus (also see Wink et al. 1998, Wink and Sauer-GĻurth 2004, Oatley et al. 2015). A partial salvaged specimen (distal right wing only) from Attu, June 1999, identified by wing chord length as a juvenile male C. cyaneus (Gibson et al. 2013), requires confirmation.
Conservation Status
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NatureServe Status

Global Status: G5
Global Status Last Reviewed: 07Apr2016
Global Status Last Changed: 22Nov1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G5 - Secure
Reasons: Range is extensive; secure, but declines have occurred in several areas, due primarily to habitat loss and degradation.
Nation: Canada
National Status: N5B,N4N,N5M (15Jan2018)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Canada Nunavut (SUB,SUM)

Other Statuses

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Not at Risk (01Apr1993)
Comments on COSEWIC: Reason for designation: Declines in numbers have been noted in some areas, but this species is widespread and relatively common. It is relatively adaptable and losses of wetland habitat have not led to population declines.

Status history: Designated Not at Risk in April 1993.

IUCN Red List Category: LC - Least concern
Convention on International Trade in Endangered Species Protection Status (CITES): Appendix II

NatureServe Global Conservation Status Factors

Range Extent: >2,500,000 square km (greater than 1,000,000 square miles)
Range Extent Comments: Breeding range in North America extends from northern Alaska to northern Saskatchewan and southern Quebec; south to northern Baja California, southern Texas, southern Missouri, West Virginia, southeastern Virginia, and North Carolina (and formerly Florida). In Eurasia, breeding occurs from the British Isles, Scandinavia, northern Russia, and Siberia south to the Mediterranean region, southern Russian, Turkestan, Amurland, Ussuriland, Sakhalin, and the Kurile Islands (AOU 1998). The species breeds rarely or erratically south of the North American breeding range (MacWhirter and Bildstein 1996). Breeding range is large but often highly discontinuous. During the nonbreeding season in North America the range extends from southern Canada or the northern contiguous United States south through the United States, Middle America, and the Antilles to northern Colombia, Venezuela, and Barbados; casual or accidental in Hawaii (AOU 1998, MacWhirter and Bildstein 1996). In North America, northern harriers winter in largest numbers in the Great Basin and central and southern Great Plains (Root 1988). The coastal areas of New York, New Jersey, Delaware, Maryland, and Virginia support the highest number of wintering birds in the Northeast (National Audubon Society 1971-74, 1982-83, 1985-87). During the nonbreeding season in Eurasia the range extends from the British Isles, southern Scandinavia, and southern Japan south to northwestern Africa, Asia Minor, India, Burma, eastern China, and the Ryukyu Islands (AOU 1998).

Number of Occurrences: > 300
Number of Occurrences Comments: This species is represented by a large number of occurrences (subpopulations).

Population Size: 10,000 - 1,000,000 individuals
Population Size Comments: Global population has been estimated at 1,300,000 birds, of which 455,000 (about 35%) occur in the United States and Canada (Rich et al. 2004). Number of breeding pairs in Canada in the early 1990s was estimated at 20,000 to 50,000 (Kirk et al. 1995).

Viability/Integrity Comments: The number of occurrences with good viability is unknown, but a large number of breeding occurrences probably have low viability.

Overall Threat Impact: Medium
Overall Threat Impact Comments: HABITAT LOSS/DEGRADATION: Population decline is primarily attributable to habitat loss and degradation. Destruction of wetlands and conversion of native grasslands to monotypic farmlands have been major sources of habitat loss (Evans 1982). The majority of southern California habitat has been lost to urbanization. In the northeastern United States, declines are attributed primarily to habitat loss from reforestation, wetland filling, and urban and industrial development in coastal areas (Serrentino 1992); also degradation of marshes by ditching (Serrentino and England 1989). Increases in intensive sheep grazing have been implicated in declining populations of Orkney Island, Scotland (Amar and Redpath 2005).

DISEASE: Rosen and Morse (1959) documented the death of Northern Harriers from the ingestion of mice contaminated with the fowl cholera bacterium, Pasteurella multocida. During an outbreak of cholera among waterfowl in California, both mountain voles (Microtus montanus) and Peromyscus spp. had ingested portions of dead birds.

CONTAMINANTS: The effects of a variety of organochlorines on raptors have been well documented in North America (Hamerstrom 1969) and Europe (Bijleveld 1974); effects include eggshell thinning, reproductive failure, and death (Newton 1979). On Long Island, New York, high levels of DDE were found in one harrier egg from an abandoned nest (Foehrenbach et al. 1970), although no evidence of eggshell thinning was observed. In North America, a mean decrease of 15% in eggshell thickness was noted between 1947 and 1969 (Anderson and Hickey 1974). Declines in both breeding and migrating harriers and the occurrence of behavioral changes coincided with the heavy use of DDT at a Wisconsin study site and elsewhere in North America. Pesticide use in Vermont (Laughlin and Kibbe 1985), Connecticut (Dowhan and Craig 1976), and New Jersey (Dunne 1984) has been implicated in population declines. A variety of biocides (DDE, dieldrin, PCBs) were found in Northern Harrier eggs collected during the 1980s on Long Island, New York. Hands et al. (1989) pointed out that few studies have been conducted on the long term effects of DDT and other biocides on harriers, with the exception of Hamerstrom (1969).

PREDATION AND HUMAN DISTURBANCE: Because harriers nest on the ground, eggs and young are vulnerable to destruction by humans and natural causes. A number of mammalian and avian predators (e.g., skunks, mink, raccoons, dogs, and other raptor species) prey upon eggs and young, and nests have been trampled by deer (Odocoileus virginianus) and livestock (Craighead and Craighead 1956, Hamerstrom 1969, Toland 1985, England 1989). Predation of harrier young has occurred when predators followed humans to nests (Watson 1977, Toland 1985). Farming activities such as mowing and harrowing may cause nest abandonment by adults (Hamerstrom 1969, Follen 1986) and destruction of nests and young (Craighead and Craighead 1956, Hamerstrom 1969, Thomas 1987). During the first half of the 1900s, mortality from shooting was common (Craighead and Craighead 1956); however, death from shooting is no longer a serious threat in North America (Bildstein 1988). In Great Britain, Watson (1977) reported that human-related mortality remained one of the most frequent causes of death for the hen harrier. Deaths also resulted from starvation and collisions with automobiles and overhead wires.

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: Although population trends vary regionally, the global population appears to be declining (MacWhirter and Bildstein 1996). The North American Breeding Bird Survey (BBS) is not the best survey method for this generally sparse raptor; where data are credible, trends are mixed. In Montana and South Dakota, BBS data indicate a declining trends for 1980-2004 (-1.0 and -2.9% per year, respectively), while in North Dakota and the Central Valley, California, increasing trends were estimated for the same time period (3.8 and 3.1%/year, respectively; Sauer et al. 2005). For 1980 to 2004, BBS data indicate a decline for the U.S., Canada, and survey-wide (-0.3, -3.0 and -1.1% per year, respectively; Sauer et al. 2005).

Numbers may fluctuate with populations of voles (Microtus) (Kirk et al. 1995).

Long-term Trend: Decline of 30-50%
Long-term Trend Comments: Declines have occurred where large wetlands and moist grasslands have been lost. Historical accounts described the harrier as abundant and widely distributed (Baird et al. 1860, Bendire 1895, Coues 1892, Bent 1937); declines in breeding harriers have since been observed in parts of North America through the late twentieth century (Arbib 1973, Evans 1982, Robbins et al. 1986, Serrentino and England 1989, Serrentino 1992). In the Northeast, breeding birds may have been extirpated in Connecticut, are restricted primarily to offshore islands in Massachusetts and Rhode Island, and remain as small and scattered populations in Vermont and New Hampshire.

BBS data indicate a significant negative trend (-3.0%/year, P<0.00, n = 269) for Canada from 1966 to 2004; for the same time period BBS data indicated a non-significant negative trend (-0.3%/year, P<0.60, n = 660) for U.S. routes and for combined U.S. and Canadian routes (-1.1%/year, P<0.02, n = 929; Saur et al. 2005).

Analyses of migratory trends showed no clear trend for northeastern North America from 1972 to 1987 (Titus and Fuller 1990). Dunne and Sutton (1986) assessed migratory data from Cape May Point, New Jersey, from 1976-85 and concluded that numbers had doubled during this period. In two studies conducted at Hawk Mountain, Pennsylvania, numbers increased slightly from 1934-66 (Spofford 1969), and no definitive trend was observed from 1934-75 by Nagy (1977). Using Hawk Mountain data from 1934-86, Bednarz et al. (1990) concluded that harriers did not show any population trend during the DDT period. Harriers exhibited a slightly positive, significant trend overall from 1934-86, and no trend was detected from 1971-86. Migration counts in Ontario increased from 1975 to 1990 (Kirk et al. 1995).

Brown (1973) analyzed Christmas Bird Count data from 45 states between 1952 and 1971; harriers showed a downward trend from 1952 to 1966 and an increase from 1966 to 1969; this increase however, was primarily attributed to populations in California. Bildstein and Collopy (1990) analyzed Christmas Bird Count data for 12 southeastern states (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, West Virginia) from 1962-64 and 1971-85 and found that wintering populations appeared to have been fairly stable since the early 1960s.

Other NatureServe Conservation Status Information

Inventory Needs: Monitor populations in areas where declines have been reported or where their status is unknown. Monitor populations at a minimum of every other year; annual monitoring may be required in areas where severe declines have occurred (Serrentino and England 1989). Expand surveys of suitable habitat to look for previously unknown populations. Area selection should be based on analyses of aerial photographs, investigations of historical breeding sites, results of Breeding Bird Atlases and Christmas Bird Counts, contacts with local birders, and element distributional modeling.

Data on density and fledgling production should be collected. Previously used or historic nesting sites should be checked for evidence of breeding activity since harriers may occupy the same site for several years. Total number of nests or females should be used to determine density and breeding success, and not the number of pairs due to their polygynous nature. Distinguish between cyclical trends that follow vole populations and longer term declines (Serrentino and England 1989).

Wintering populations should also be monitored. Surveys of suitable hunting habitats should be conducted by experienced observers. Data collected on surveys should include: (1) the number of birds observed, sex and age (juvenile vs. adult); (2) weather variables, since flight activity is affected by weather conditions (Bildstein 1978); and (3) hunting habitat and roost site selection (Serrentino 1992).

Distribution
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Breeding range in North America extends from northern Alaska to northern Saskatchewan and southern Quebec; south to northern Baja California, southern Texas, southern Missouri, West Virginia, southeastern Virginia, and North Carolina (and formerly Florida). In Eurasia, breeding occurs from the British Isles, Scandinavia, northern Russia, and Siberia south to the Mediterranean region, southern Russian, Turkestan, Amurland, Ussuriland, Sakhalin, and the Kurile Islands (AOU 1998). The species breeds rarely or erratically south of the North American breeding range (MacWhirter and Bildstein 1996). Breeding range is large but often highly discontinuous. During the nonbreeding season in North America the range extends from southern Canada or the northern contiguous United States south through the United States, Middle America, and the Antilles to northern Colombia, Venezuela, and Barbados; casual or accidental in Hawaii (AOU 1998, MacWhirter and Bildstein 1996). In North America, northern harriers winter in largest numbers in the Great Basin and central and southern Great Plains (Root 1988). The coastal areas of New York, New Jersey, Delaware, Maryland, and Virginia support the highest number of wintering birds in the Northeast (National Audubon Society 1971-74, 1982-83, 1985-87). During the nonbreeding season in Eurasia the range extends from the British Isles, southern Scandinavia, and southern Japan south to northwestern Africa, Asia Minor, India, Burma, eastern China, and the Ryukyu Islands (AOU 1998).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The maps for birds represent the breeding status by state and province. In some jurisdictions, the subnational statuses for common species have not been assessed and the status is shown as not-assessed (SNR). In some jurisdictions, the subnational status refers to the status as a non-breeder; these errors will be corrected in future versions of these maps. A species is not shown in a jurisdiction if it is not known to breed in the jurisdiction or if it occurs only accidentally or casually in the jurisdiction. Thus, the species may occur in a jurisdiction as a seasonal non-breeding resident or as a migratory transient but this will not be indicated on these maps. See other maps on this web site that depict the Western Hemisphere ranges of these species at all seasons of the year.
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
Canada NU

Range Map
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Ecology & Life History
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Basic Description: Slender, medium sized hawk, 46-50 cm (18-20 in.) with a wingspan of 102-118 cm (40-46 in.). Low-flying; wings held in a strong 'V' during flight (MacWhirter and Bildstein 1996). Adult male is gray on the back with a lighter underside, black wingtips, and white rump. Adult female is larger than male, brown on the back with a brown and white (buff) striped underside, and white rump. Juvenile is similar to adult female with a darker brown back and russet underside.
General Description: MORPHOLOGY AND PLUMAGES: Members of the genus Circus are slim, medium-sized hawks with long, broad wings and long legs and tails. A characteristic facial ruff gives them an owl-like appearance (Brown and Amadon 1968). The adult female is dark brown above and buffy below, with some streaking on the underparts. The tail is barred. The mean weight is 529.9 grams (Hamerstrom 1986), total length varies from 48-61 centimeters and wingspread ranges from 110-137 centimeters (Bildstein 1988).

The adult male is pale gray above and white below with reddish spots on the underparts. The wingtips are edged with black. Males up to three to four years of age have brown markings dorsally (Bildstein 1988). The mean weight of the adult male is 367.4 grams (Hamerstrom 1986), total length ranges from 44-51 centimeters, and wingspread varies from 102-114 centimeters (Bildstein 1988).

The immature harrier appears similar in color to the adult female, but has a cinnamon-colored breast and darker brown back and wings (Bent 1937, Brown and Amadon 1968). This distinctive immature plumage is retained throughout the first winter into the following spring and, in some cases, summer. During spring and early summer it is difficult to discriminate between brown harriers (i.e., immatures from adult females) (Bildstein 1988).

VOCALIZATIONS: The call given by adult and immature harriers when they are alarmed or excited has been described as a "rapid chattering," "ke-ke-ke," or "chek-ek-chek-ek" (Brown and Amadon 1968). The begging call has been described as a "wailing squeal," given by the female to the male, and juveniles to adults when begging for food. This call is also used during courtship by the male and female (Bent 1937, Brown and Amadon 1968, Balfour and MacDonald 1970, Watson 1977). When incubating the female may utter a "quip quip quip" (Brown and Amadon 1968).

EGGS: Eggs are pale blue at laying and turn white in a few days; brown markings may occur (Hamerstrom 1969).

Diagnostic Characteristics: Adults and immatures of both sexes have a distinctive, white rump patch.
Reproduction Comments: BREEDING CHRONOLOGY: Spring arrival dates on breeding grounds in the Northeast range from mid-March to early April, and laying dates range from mid-April to mid and late June (Bent 1937, Hall 1983, Laughlin and Kibbe 1985). Clutches are laid over a period of about nine days, with eggs being laid at two-day intervals (Hamerstrom 1969). Clutch size usually varies from four to six eggs (Bent 1937, Hamerstrom 1969, Duebbert and Lokemoen 1977). Incubation is 30-32 days and begins before the last egg is laid; as a result, hatch is asynchronous (Breckenridge 1935, Hamerstrom 1969). The nestling period varies from 30-41 days (Urner 1925, Hamerstrom 1969, England 1989). Juveniles stay near the nest and are dependent on their parents for food for an additional three to four weeks (Breckenridge 1935, Hamerstrom 1969).

COURTSHIP AND BREEDING BEHAVIOR: The distinctive courtship flight has been called a "sky dance." The flight is performed by the male, and occasionally by the female, and consists of a series of nose dives or U-shaped dives (Bent 1937). Hamerstrom (1986) illustrated the behavior as a series of circular flights when viewed from the front. Copulation occurs either on the ground or on a short perch (Brown and Amadon 1968, Clark 1972). The female apparently solicits the male with the begging or food call. Harriers do not appear to mate for life (Hamerstrom 1969).

Both sexes may breed in their first year (Watson 1977); however, more females usually breed as yearlings than males (Hamerstrom et al. 1985, England 1989). In Wisconsin, the majority of females bred at one year of age (Hamerstrom et al. 1985). The number breeding as yearlings (both males and females) in Wisconsin (Hamerstrom et al. 1985) and New Brunswick (Simmons et al. 1986) increased during periods of high meadow vole abundance.

Although the male, female, or both may choose the nest site, the female appears to do the majority of nest building. Both parents bring nest material (Watson 1977, Toland 1985). The nest is built on the ground and is composed of dead grasses, weeds, and small twigs (Urner 1925, Bent 1937, Hecht 1951). Nests are frequently placed in dense vegetation (Duebbert and Lokemoen 1977, Hamerstrom and Kopeny 1981, Toland 1985, Serrentino 1987). Larger and deeper nests are often built in wet or flood-prone areas (Urner 1925, Sealy 1967). Sealy (1967) measured 12 nests in upland and wetland habitats; depths of nests ranged from 5.0-24.0 centimeters, and diameters varied from 39.0-63.0 centimeters. Harriers may use the same patch of shrubs, field, or general area for several years (Sealy 1967, Balfour and Cadbury 1979, Serrentino 1987, England 1989).

Incubation and feeding of the young is done by the female only (Hamerstrom 1969). During incubation and the early portion of the nestling stage, the female rarely leaves the nest. At this time she is supplied with food by the male, accomplished by a "food pass" in which the male drops the prey to her in mid-air over or near the nest (Breckenridge 1935, Hecht 1951). When she is absent, he drops the prey into the nest and usually leaves immediately (Breckenridge 1935). When the nestlings are about two weeks old, the female leaves the nest to hunt more frequently (Hecht 1951, Schipper 1973).

NESTLING DEVELOPMENT: Newly-hatched harriers are covered with a layer of white down. Their eyes open a few hours after hatching. Mean weight at hatching is 19.8 grams (Scharf and Balfour 1971). For the first five days, the nestlings are almost continually brooded by the female (Hecht 1951). Between two and three weeks of age the young begin to make tunnels in the vegetation adjacent to the nest. These tunnels may be used as escape routes (Balfour and MacDonald 1970). Between the third and fourth weeks, the young lose most of their down and acquire their distinctive juvenal plumage (Watson 1977). The young are usually able to fly at 30 days, and have become fairly proficient flyers at 35 days (Hammond and Henry 1949). The lightest individuals and those with the most well developed flight feathers, usually the males, fledge first (Scharf and Balfour 1971).

Because hatching occurs asynchronously, the nest contains young of varying sizes. The smallest nestlings often do not survive because of competition for food with their larger nest-mates (Breckenridge 1935, Balfour and MacDonald 1970). Female nestlings are larger than males for most of the nestling period (Scharf and Balfour 1971, Picozzi 1980).

LONGEVITY: The average life span is approximately seven years in the wild (Brown and Amadon 1968). The longest life span of a banded, free-ranging, individual was 16 years, 5 months (Clapp et al. 1982). Juvenile mortality has been attributed to starvation and malnutrition (Craighead and Craighead 1956). In Great Britain, mortality was highest for first-year birds (Balfour and Cadbury 1975, Watson 1977). In the Orkney Islands, survival of hen harriers increased from 32% in the first year to 70% in the following year (Balfour and Cadbury 1975).

NESTING SUCCESS: Hatching success varies greatly both among years and study areas. In Michigan, yearly hatching success varied from 0-78% (Craighead and Craighead 1956) and in Canada from 23-89% (Sealy 1967). Fledgling production, i.e., the number of young fledged per female (monogamous females only) varied as follows: 1.5-2.3 for all nests, including those that failed (Craighead and Craighead 1956, Picozzi 1978, Balfour and Cadbury 1979, Hamerstrom et al. 1985, England 1989), and 2.7-3.1 for successful nests (Picozzi 1978, Balfour and Cadbury 1979, Hamerstrom et al. 1985, England 1989). For data on fledgling production for polygynous females, see Balfour and Cadbury (1979), Hamerstrom et al. (1985), Simmons et al. (1986), and England (1989).

The frequency of renesting after nest failure is low. Renesting has been documented in populations studied in New Brunswick (Simmons 1984), Michigan (Craighead and Craighead 1956), and the Dakotas (Duebbert and Lokemoen 1977). In Wisconsin (Hamerstrom 1969) and New York (England 1989), harriers did not lay replacement clutches. In Wisconsin, the adults left the study area within 24 hours of nest failure (Hamerstrom 1969).

POLYGYNY: Polygyny has been well documented (Breckenridge 1935; Hecht 1951; Clark 1972; Balfour and Cadbury 1979; Hamerstrom et al. 1985; Simmons et al. 1986; England 1989). In mainland Scotland, the frequency of polygynous matings was low (Picozzi 1978). However, in the Orkney Islands in Scotland, polygyny accounted for a majority of the mating associations in some years (Balfour and Cadbury 1975, Balfour 1979; Picozzi 1984). In Wisconsin and New Brunswick, the occurrence and frequency of polygyny was related to meadow vole abundance. High vole numbers led to increases in (1) the numbers nesting, (2) the number of yearlings nesting, and (3) the occurrence of polygyny. Simmons et al. (1986) concluded that the frequency of polygynous matings increased during high vole years because males were able to provision more females successfully. In the Orkney Islands and on Long Island, New York, the occurrence of polygyny was related to an unbalanced sex ratio that resulted in a shortage of male breeders (Picozzi 1984, England 1989). Balfour and Cadbury (1979) noted that polygyny was fairly rare until the 1950s, when the population began to increase from a low point. Between the 1950s and 1960s more females than males were reared in the population (Picozzi 1984); during recent years, more males than females have fledged.

Ecology Comments: NONBREEDING: May aggregate in communal roosts in winter in areas of high prey density (Evans 1982; see also Palmer 1988). In winter, may hunt in same area for several consecutive days (see Palmer 1988). In the nonbreeding season, females may defend preferred feeding areas against males. Vegetation structure affects harrier habitat selection and hunting behavior. Harriers often increase flight altitude with increasing vegetation height, enabling them to "see" into the vegetation (Schipper 1977, Serrentino 1987). In a freshwater marsh in Florida, harrier hunting success was negatively affected by the dense marsh grasses that concealed their primary prey, the cotton rat (SIGMODON HISPIDUS) (Collopy and Bildstein 1987).

BREEDING DENSITY AND DISPERSION: Breeding density about 0.8-6.4 females per ten square kilometers (see Serrentino 1992). Breeding density and dispersion of are affected by the abundance of prey species (Hamerstrom 1979), the occurrence of polygyny (Balfour and Cadbury 1979, Simmons et al. 1986), nest site fidelity (Sealy 1967, Balfour and Cadbury 1979), and habitat quality (Picozzi 1984, Simmons and Smith 1985). The number of nesting harriers increases during high meadow vole abundance in those populations that prey primarily on voles (Hamerstrom 1969, 1979; Clark 1972; Simmons et al. 1986). In Wisconsin (Hamerstrom 1979) and New Brunswick (Simmons et al. 1986), nest densities increased more than twofold when vole abundance rose from low to high. Polygyny tends to increase the degree of nest clumping in breeding populations (Balfour and Cadbury 1979, Simmons et al. 1986, England 1989). In Orkney, the distance between nests decreased with increasing harem size (Picozzi 1984). Harriers often occupy the same nest sites or nesting territories, but not the nest itself, for several years (Sealy 1967, Balfour and Cadbury 1979, Serrentino 1987, England 1989). In New Hampshire, a pair nested in the same field for a minimum of five years (Serrentino 1987).

Both Picozzi (1984) and Simmons and Smith (1985) noted that high densities of breeding harriers in some areas were probably a reflection of habitat quality. At a moorland site in mainland Scotland (Picozzi 1978), nest densities were much lower than densities on the Orkney Islands (Balfour and Cadbury 1979). Differences between the two areas included an abundance of prey in the farmlands and wetlands at Orkney (Picozzi 1984). Simmons and Smith (1985) postulated that harrier nest densities at a predominantly wet marsh in New Brunswick were higher than those reported in other areas because of increased availability of nest sites and high densities of meadow voles.

HUNTING RANGE SIZE: The sizes of hunting ranges vary widely during the breeding season in different areas, presumably because of differences in habitat types, availability of prey species, distribution of nest sites, and stage of the breeding cycle (Craighead and Craighead 1956, Balfour and MacDonald 1970, Balfour and Cadbury 1979, Serrentino 1992). In two midwestern studies, the range sizes for pairs varied from 2.6-5.5 kilometers squared (Breckenridge 1935, Craighead and Craighead 1956). Males usually have larger hunting ranges than females (Hecht 1951, Schipper 1977, Watson 1977). Schipper (1977) reported range sizes from 1.8-12.3 kilometers squared for males in the Netherlands, and Martin (1987) observed range sizes from 9.7-17.7 kilometers squared for males in Idaho. Hunting range sizes of approximately 0.8-5.4 kilometers squared for females were observed in both the Netherlands and New Hampshire (Schipper 1977, Serrentino 1987). In North Dakota, breeding harriers were found only in grassland patches greater than 100 hectares, and were encountered in large patches more often than statistically expected (Johnson and Igl 2001).

Little data are available on the range sizes of nonbreeding harriers. In Michigan, wintering birds flew up to eight kilometers from roost sites to hunting ranges (Craighead and Craighead 1956). The number hunting in a particular area decreased with increasing distance from the roost, and hunting range size varied from 0.12-2.6 kilometers squared. In the Netherlands, appeared to have fixed hunting ranges of unidentified sizes (Schipper et al. 1975).

WEATHER: Cold or rainy weather may negatively affect breeding success. Egg-laying may be delayed by cold weather (Watson 1977, Schipper 1979). Prolonged periods of rainy weather, particularly during the incubation and nestling stages, may cause nest desertion or death of nestlings from exposure (Follen 1986, Simmons et al. 1986). Abnormally high tides have destroyed nests in coastal areas (Dunne 1986).

PARASITES: Raptors are susceptible to a number of bacterial and viral diseases. Numerous species of endoparasites, blood protozoans, and ectoparasites have been recorded in raptors. Little is known of the effects of diseases and parasites on wild populations because of the scarcity of data and the difficulty associated with separating the direct causes of death from diseases and parasites with the indirect causes (e.g., birds weakened by disease may succumb to death from predation, starvation and severe weather) (Newton 1979). External and internal parasites have been found on free-living northern harriers (Peters 1936, Scharf 1966, Hamerstrom 1969, Anderson and Freeman 1969, Pence 1973).

Non-Migrant: N
Locally Migrant: Y
Long Distance Migrant: Y
Mobility and Migration Comments: Generally arrives in northern breeding areas in March-April (and May in Alaska). Northward migration may continue in an area even after local nesting has begun. Southward migration in the U.S. and Canada occurs August-November. Northern breeders may migrate farther south than do some more sedentary populations breeding at lower latitudes (Palmer 1988). In Costa Rica, arrives in early October, departs by early May (Stiles and Skutch 1989).

During migration, harriers move in a broad front at heights up to 770 m (Kerlinger 1989). They have been observed traveling along both coastal and inland ridges at numerous sites in eastern North America (Nagy 1977, Bildstein et al. 1984, Heintzelman 1986, Dunne and Sutton 1986). Sattler and Bart (1984) stated that harriers may not be as conspicuous as other raptors during migration because of their frequent use of flapping flight versus soaring, and their tendency to migrate individually or in small flocks. Harriers do not appear to avoid crossing water during migration. They have been seen "island hopping" in Maine, and have been observed in Bermuda, the Bahamas, and the West Indies (Bildstein 1988, Kerlinger 1989).

Most of the information on harrier migration comes from the autumn season. In the Northeast, the peak of fall migration occurs during September in Maine (Appell 1986), from the last week in September to the first week in October in Rhode Island (C. Raithel, pers. comm.), and from early October to mid-November in Maryland (Stewart and Robbins 1958). In West Virginia, one or two harriers are usually observed migrating over the eastern mountain ridges from September to early October (Hall 1983). At Hawk Mountain in Pennsylvania, the peak period for harrier migration is October and November, although their entire migratory period ranges from August to November (Broun 1939, Spofford 1969, Nagy 1977). During August and September, immature harriers are the most common, followed by both adults and immatures in varying numbers in October. Adult males are predominant later in the season (Nagy 1977). Using data from four raptor banding stations (Cape May Point and Kittatinny Mountain, New Jersey; Hawk Cliff, Ontario; and Duluth, Minnesota), Bildstein et al. (1984) found similar trends in the timing of migration with respect to sex and age as that observed by Nagy (1977) at Hawk Mountain.

During the spring migration in central Wisconsin, adult males preceded both adult females and immatures, and adult females arrived before immatures at potential breeding areas (Hamerstrom 1969). On Long Island, New York, males also arrived at breeding sites before females (England 1989).

RECOVERIES: Hammond and Henry (1949) banded 150 nestling harriers in North Dakota and received returns on 12 (8%). The birds had dispersed in a general southern direction, with recoveries from North Dakota (one), Kansas (one), Texas (six), Louisiana (one), Mexico (one), and British Columbia (one). More than half the birds were recovered within one year (seven of 12). Between 1959 and 1977, 12 returns were received from harriers banded as nestlings on the Buena Vista Marsh in Wisconsin (F. Hamerstrom, pers. comm., cited by Beske 1982). The birds had migrated in a general south-southeasterly direction and all were recovered during their first fall and winter. Returns were from the following states: Wisconsin (one), Michigan (two), Illinois (two), Tennessee (one), Mississippi (one), Alabama (one), Georgia (one), Florida (one), South Carolina (one), and North Carolina (one).

Estuarine Habitat(s): Herbaceous wetland
Palustrine Habitat(s): Bog/fen, HERBACEOUS WETLAND
Terrestrial Habitat(s): Alpine, Cropland/hedgerow, Grassland/herbaceous, Tundra
Habitat Comments: BREEDING: Marshes, meadows, grasslands, and cultivated fields. Perches on ground or on stumps or posts. Nests on the ground, commonly near low shrubs, in tall weeds or reeds, sometimes in bog; or on top of low bush above water, or on knoll of dry ground, or on higher shrubby ground near water, or on dry marsh vegetation.

NORTHEAST: A wide range of open habitats and vegetative associations are used, including abandoned fields, upland maritime heaths, wet hayfields, salt marshes, and cattail marshes (Serrentino 1992). Nests are placed on the ground, usually in dense cover. Nesting sites have included abandoned fields in dense stands of meadowsweet (Spiraea latifolia) or red-osier dogwood (Cornus stolonifera) in New Hampshire (Serrentino 1987), upland maritime heaths comprised of northern bayberry (Myrica pensylvanica), black huckleberry (Gaylussacia baccata) and wild rose (Rosa spp.) in Massachusetts (Holt and Melvin 1986), and in wet hayfields dominated by reed canary grass (Phalaris arundinacea) in Vermont (Laughlin and Kibbe 1985). Breeding sites in New Jersey saltmarshes on the Atlantic coast have been found in pure stands of common reed (Phragmites australis), as well as in salt hay grass (Spartina patens) and smooth cordgrass (Spartina alterniflora) (Dunne 1984). On Long Island, nests were found in stands of common reed and poison ivy (Toxicodendron radicans) (England 1989).

Other nesting habitats in the Northeast are cattail marshes (Laughlin and Kibbe 1985, Serrentino 1989), bogs (Hall 1983, Laughlin and Kibbe 1985, Andrle and Carroll 1988), native grassland prairies (Genoways and Brenner 1985), and dwarf conifer forest (England 1989). In other regions of North America, harriers nest in a variety of upland and wetland habitats such as willow (SALIX spp.) swales and meadows (Hamerstrom and Kopeny 1981), pure stands of blackberry (RUBUS spp.) (Toland 1985), hayfields and cropland (Duebbert and Lokemoen 1977, Follen 1986) and undisturbed grass/legume vegetation (Duebbert and Lokemoen 1977).

CALIFORNIA: In California, habitats include freshwater marshes, brackish and saltwater marshes, wet meadows, weedy borders of lakes, rivers and streams, annual and perennial grasslands (including those with vernal pools), weed fields, ungrazed or lightly grazed pastures, some croplands (especially alfalfa, grain, sugar beets, tomatoes, and melons), sagebrush flats, and desert sinks (MacWhirter and Bildstein 1996, J. Silveira in litt., J. Seay in litt.) (Shuford and Gardali 2008). Harriers nest on the ground, mostly within patches of dense, often tall, vegetation in undisareas (MacWhirter and Bildstein 1996).

NON-BREEDING: In the Northeast, winter in greatest numbers in the saltmarshes of the Atlantic coast, with the winter population exhibiting a tendency to increase from north to south (National Audubon Society 1971-74, 1982-83, 1985-87). Although harriers appear to prefer coastal regions in the Northeast, they will range inland during the winter when suitable open habitats are available (Root 1988), though avoiding the mountainous interior. Other habitats used by harriers during the nonbreeding season in both coastal and inland areas include agricultural fields (croplands, hayfields, and pastures), abandoned fields, and freshwater wetlands. Elsewhere in North America, wintering harriers have been observed in habitats similar to those in the Northeast (Craighead and Craighead 1956, Bildstein 1978, Temeles 1986, Collopy and Bildstein 1987, Littlefield and Thompson 1987).

WINTER ROOSTS: Communal roosting flocks may be formed during the nonbreeding season, beginning in October and often breaking up at the onset of spring migration (Bildstein 1979). Harriers roost on the ground in open habitats such as agricultural and abandoned fields, and saltmarshes (Weller et al. 1955, Mumford and Danner 1974, Bildstein 1979, Evans 1982, Bosakowski 1983). The same roost may be used for several nights or for several months (Bent 1937, Craighead and Craighead 1956). The number of birds using roosts varies from several to 60 individuals, and roosts may be shared with short-eared owls (Asio flammeus). Roost sites may be abandoned during periods of flooding or heavy snow (Bildstein 1979) or when prey becomes depleted in areas adjacent to roosts (Craighead and Craighead 1956, Bildstein 1979).

HUNTING HABITAT: Selection of hunting habitat is affected by several parameters including proximity to the nest site (Schipper 1977, Martin 1987, Serrentino 1987), sex and age of the individual (Schipper et al. 1975, Bildstein 1978, Marquiss 1980), prey abundance and availability (Schipper et al. 1975), vegetation structure (Schipper et al. 1975, Temeles 1986), and the presence of competitors (Temeles 1986). During the breeding season, females often hunt in areas adjacent to the nest site (Schipper 1977, Martin 1987, Serrentino 1987). Males hunt farther from the nest where they may encounter habitat types different than those located adjacent to nests.

Differences in habitat selection have been observed among adult females, adult males, and juveniles. In Ohio, intersexual differences in habitat selection were related to prey choice (Bildstein 1978). Females were observed significantly more often than males in fallow fields where small mammals were common. Adult males preferred corn stubble where avian prey was predominant. Males took more birds than females (40% vs. 4%), while females were principally small mammal specialists (93% for females versus 56% for males). Unsexed juveniles relied primarily on mammals.

Harriers select habitats on the basis of the availability and abundance of prey species. In the Netherlands, harriers preyed upon common voles (Microtus arvalis) in agricultural areas when voles were accessible and populations were high (Schipper et al. 1975). However, when voles became concealed by heavy snowfall, harriers hunted in reedbeds where avian prey was common.

During the nonbreeding season harriers may defend hunting territories (Temeles 1986). In California, females defended hunting territories against other females and males, and aggressively excluded males from preferred hunting habitats such as fallow fields. The substantial size difference between male and female harriers is probably responsible for female dominance of males.

Adult Food Habits: Carnivore
Immature Food Habits: Carnivore
Food Comments: Depending on availability, eats small mammals (especially voles and cotton rats), small and medium-size birds (especially passerines), and some reptiles, amphibians, large insects, carrion. Hunts over open land or marshes; usually flies low when hunting, captures prey on ground.(Palmer 1988) During the breeding season, young are fed primarily small mammals and birds. In Pennsylvania, a variety of birds, mostly juvenile, were important prey for the young, and included northern flickers (Colaptes auratus), eastern meadowlarks (Sturnella magna), red-winged blackbirds (Agelaius phoeniceus), bobolinks (Dolichonyx oryzivorus), American robins (Turdus migratorius), and mourning doves (Zenaida macroura) (Randall 1940). Other prey taken were several species of mice (Microtus, Peromyscus, and Zapus spp.), frogs (Rana spp.), and garter snakes (Thamnophis sirtalis). In New Hampshire, microtine rodents and small and medium-sized birds were the most common prey of harriers (Serrentino 1987). When prey could be identified, the following were noted; shorttail shrew (Blarina brevicauda), meadow vole (Microtus pennsylvanicus), meadow jumping mouse (Zapus hudsonius), ruffed grouse (Bonasa umbellus), northern flicker, American robin, bobolink, and garter snake. In a population breeding on the barrier beaches of Long Island, New York, the meadow vole was the primary prey, with avian species being of secondary importance (England 1989). Waders and passerine birds were the avian groups represented in greatest frequency in prey remains.

Small mammals and birds were also the most important prey taken in other North American studies (Breckenridge 1935, Hecht 1951, Craighead and Craighead 1956, Toland 1985). Harriers in New Brunswick concentrated on meadow voles early in the breeding season, with juvenile birds becoming the most common prey item during the mid and late nestling stages (Barnard et al. 1987).

In Michigan and Ohio, prey taken in winter consisted primarily of meadow voles (Craighead and Craighead 1956, Bildstein 1978). In Pennsylvania, several rodent species (Microtus, Peromyscus, and Zapus spp.), cottontail rabbits (SYLVILAGUS spp.), and birds were common in the fall and winter diets of harriers (Randall 1940). At a freshwater marsh in Florida, the birds preyed primarily on cotton rats (Collopy and Bildstein 1987). Godfrey and Fedynich (1987) reported that harriers appeared to take waterfowl opportunistically in Texas.

During the breeding season, high prey densities have been associated with increased breeding success (Hamerstrom et al. 1985, Simmons et al. 1986). The number of breeding harriers increased during periods of high meadow vole abundance in Wisconsin (Hamerstrom 1979, Hamerstrom et al. 1985) and New Brunswick (Simmons et al. 1986). Hamerstrom et al. (1985) noted that nesting success showed a slightly positive relationship with vole abundance. In New Brunswick, clutch size was positively correlated with vole indices and high provisioning rates by males were associated with an increase in the number surviving to fledging (Simmons et al. 1986). The starvation of nestlings was more common during vole population lows.

Harrier density and distribution may be affected by prey abundance during the winter. The number observed at winter roosts increased during winters when meadow vole abundance was high (Weller et al. 1955, Craighead and Craighead 1956). Bildstein (1979) also observed that the placement of roost sites was related, in part, to the density of prey in the surrounding areas. Roost sites were commonly situated in the center of the birds' hunting areas.

Adult Phenology: Crepuscular, Diurnal
Immature Phenology: Crepuscular, Diurnal
Phenology Comments: May hunt throughout day; mostly in early morning and late afternoon in some areas (Evans 1982). In winter, spends much of daylight period perched, as opposed to flying.
Length: 58 centimeters
Weight: 531 grams
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Breeds in a wide range of open habitats across much of the Northeast, including abandoned fields, upland maritime heaths, wet hayfields, saltmarshes, and cattail marshes. Nesting sites are chosen based on their availability and the abundance of prey in adjacent areas. Harriers feed their young primarily small mammals and birds. In high quality habitats with abundant prey, tend to nest in greater densities and form polygynous mating associations. From August to November, northeastern harriers migrate to their wintering grounds in the saltmarshes of the Atlantic coast where they may form communal roosting flocks on the ground in open habitats.

The Northeast regional population has remained stable from 1966-87 according to data from the BBS; however, the bird may be easily overlooked during the nesting period when the female rarely leaves the nest. Population declines have been documented in several northeastern states and have been attributed primarily to habitat loss from reforestation, the filling of wetlands, and urban and industrial development in coastal areas. Limited data is available for populations in several states. Populations should be monitored across the Northeast by checking previously used or historic nesting sites for evidence of breeding at least every other year. Wintering populations should also be observed by surveying suitable hunting habitats. Both breeding and wintering habitats should be protected and managed to provide a complex of several different undisturbed habitat types for nesting and hunting (Serrentino 1992).

Preserve Selection & Design Considerations: The amount of land required to maintain a viable population has not been established. Breeding and wintering densities will vary between areas because of differences in habitat types, availability and density of prey species, availability and distribution of suitable nesting sites, and the frequency of polygyny (Craighead and Craighead 1956, Clark 1972, Picozzi 1978, Balfour and Cadbury 1979, Hamerstrom et al. 1985). F. Hamerstrom (pers. comm., cited by Hands et al. 1989) recommended that an adequate amount of habitat should be protected to support more than four females during the breeding season.

The results of several long-term studies can provide land managers with general estimates of the size requirements necessary for the maintenance of breeding populations. At a 160 sq km site in Wisconsin, between four and 34 harrier nests were found per year (Hamerstrom et al. 1985). In New Brunswick, a 60 sq km portion of the reclaimed Tantramar Marsh supported 12-37 nests over a five year period (Simmons et al. 1986). At a 120 sq km site in Scotland, between five and 15 nests per year were found (Picozzi 1978). A 26 sq km portion of barrier beach on Long Island, New York, supported from nine to 14 nests each year (England 1989).

Management Requirements: Protection of favorable habitat and of nest sites are important; nests should not be disturbed during the early part of the nesting cycle, especially prior to hatching. Wetland preservation aimed primarily at waterfowl and habitat management programs for prairie chickens are beneficial to this species (Evans 1982).

The implementation of a management plan in the Northeast requires more detailed and accurate data on abundance and current population trends, habitat and area requirements, and more specific information, such as prey selection and predation rates. The following discussion of management recommendations for the northern harrier is based, in part, on Serrentino and England (1989); however, most of the information necessary to design a concise and scientific plan is currently lacking.

HABITAT PRESERVATION: Habitat loss and degradation are most likely the primary causes of the decline of the harrier in the northeastern region (Dowhan and Craig 1976, Laughlin and Kibbe 1985, Robbins and Boone 1985, England 1989, Serrentino and England 1989). If the current trend of land use patterns continues, open land will decline and the amount of developed area will increase (Brooks 1989). Habitat preservation is imperative in states where remnant populations are (1) confined to islands or small areas of suitable habitat on the mainland, or (2) threatened by development of coastal areas, drainage of wetlands, reforestation, and other forms of habitat loss (Serrentino and England 1989).

HABITAT MANAGEMENT: Harriers will breed and winter in a wide range of open lands provided that the following are available: (1) suitable breeding sites (e.g., cattail marshes, wet meadows, and shrub uplands and wetlands); (2) hunting habitats, such as early successional fields, grasslands, and wet meadows; and (3) an adequate prey base, comprised primarily of small mammals and birds. Harriers breed in areas managed for prairie chickens (TYMPANUCHUS spp.) that consist of early successional fields and dry and wet habitats (Hamerstrom 1969, 1979; Hamerstrom et al. 1985). Harrier breeding habitat in New Brunswick is composed of cattail marshes, wet meadows, upland hayfields, and abandoned fields (Simmons and Smith 1985). In northern New Hampshire, harriers continue to nest in an area where dairy farming and timber harvesting are the primary forms of land use (Serrentino 1987). Crops are rarely grown, and hayfields, abandoned fields, and shrub wetlands are common. Harriers breed in areas managed for waterfowl in the Dakotas, where fields are maintained in early successional stages composed of planted grass and legume species (Duebbert and Lokemoen 1977).

Management areas consisting of a complex of several different habitat types, such as dense shrublands and grasslands (dry and wet) and marshes may benefit breeding harriers. Nests have been found in areas where the dominant shrubs ranged from 0.5-2.0 meters (Holt and Melvin 1986, Toland 1985, Serrentino 1987). In grasslands in the Dakotas, harriers nested in vegetation ranging in height from 30 centimeters to more than 60 centimeters (Duebbert and Lokemoen 1977). The dead vegetation remaining from previous growing seasons was an important component in nest site selection. At least one harrier nest was present in fields ranging in size from 11-54 hectares. Harriers have nested in wet meadows comprised of bluejoint (CALAMAGROSTIS CANADENSIS) and prairie cordgrass (SPARTINA PECTINATA) (Simmons and Smith 1985). Cattail marshes are also important nest sites and, in some studies, predation rates were lower in these habitats compared to drier areas (Sealy 1967, Simmons and Smith 1985).

Harrier hunting habitats must be capable of providing an adequate prey base for breeding, wintering, and migrating birds. The maintenance of early successional stages is recommended. Small mammals prefer abandoned fields and other disturbed habitats with vegetation cover consisting of dense grasses and weeds (Birney et al. 1976, Baker and Brooks 1981). In contrast, extensive croplands and hayfields that are subjected to several annual cuttings may depress small mammal populations. Burning, grazing, mowing, and disking may be used to encourage early successional stages. The timing and frequency of these treatments would depend on characteristics of the particular site (e.g., location or successional stage).

PROTECTION OF NEST SITES: Nests should be protected from disturbance by recreational activities (e.g., off-road vehicle use), timber operations (cutting and bulldozing), certain agricultural operations (mowing, plowing, etc.), and unnecessary nest visitations from both researchers and the public. Nest visitations should be avoided during the early part of the nesting cycle, especially from the pre-laying and egg-laying stages up to hatching (Hamerstrom 1969, Fyfe and Olendorff 1976). Predation of harrier young has occurred when predators followed humans to nests (Watson 1977, Toland 1985). In agricultural areas, haying and tilling has destroyed nests and young (Craighead and Craighead 1956, Thomas 1987).

The use of buffer zones around nest sites may be necessary in areas where human-related disturbance is likely to occur. The size of these buffers has not been established and would most likely vary with the habitat type surrounding the nest, nature of the disturbance, stage of the nesting cycle, and the individual behavior of the pair (White and Thurow 1985; P. Serrentino, pers. obs.). Harriers will tolerate some agricultural activities during the breeding season. In New Hampshire, harriers nested in shrub wetlands and uplands adjacent to hayfields (Serrentino 1987) and did not seem disturbed by haying operations, perhaps because of familiarity with the activity. In addition, the availability of suitable nesting habitat adjacent to agricultural fields may have prevented the birds from using the hayfields as nest sites. In Wisconsin, farmers left the area around nests unmowed or unplanted (Follen 1986). Follen, 1986, also reported that nests in agricultural fields were abandoned or females left eggs or young for long periods during rainy weather when farmers were plowing.

PUBLIC EDUCATION: A public education campaign would benefit harriers by increasing the awareness of this raptor's status in the region.

Monitoring Requirements: Populations should be monitored in areas where decreases have occurred or when the status of the population is unknown (Serrentino and England 1989). Surveys of suitable habitats should be undertaken to look for previously unknown populations of birds. These areas can be chosen from analyses of aerial photographs, investigations of historical breeding sites, the results of Breeding Bird Atlases and Christmas Bird Counts, and contacts with local birders.

To monitor breeding populations, data on density and fledgling production should be collected. Previously used or historic nesting sites should be checked for evidence of breeding activity since harriers may occupy the same site for several years. Because harriers may be polygynous, the total number of nests or females should be used to determine density and breeding success, and not the number of pairs. Surveys should be conducted at a minimum of every other year. In areas where severe declines have occurred, yearly surveys may be required. Because nest density may track small mammal populations, a decrease in the number of nesting birds may be the result of a low vole year and not the beginning of a serious decline, provided that habitat availability remains constant (Serrentino and England 1989).

Wintering populations should also be monitored. Information provided by Christmas Bird Counts can be used to identify areas that support high numbers of birds. Surveys of suitable hunting habitats should be conducted by experienced observers throughout the winter. Data collected on surveys should include: (1) the number of birds observed, and sex and age (juvenile vs. adult) when possible; (2) weather variables, since flight activity is affected by weather conditions (Bildstein 1978); and (3) if time permits, hunting habitat and roost site selection (Serrentino 1992).

Management Research Needs: Regional Management Program. - A regional management program should be implemented in the Northeast for species that remain threatened by continued habitat loss. It may also be possible to design a management plan that would include other threatened species with similar habitat requirements such as the short-eared owl (S. Melvin and G.R. Tate, pers. comms.). Particular question which need to be researched before a regional plan can be implemented include: (1) can populations be maintained in areas where agriculture is declining; (2) should management efforts concentrate on breeding and wintering populations that occur in traditional habitats such as inland and coastal wetlands; and (3) how can key habitats be preserved in areas where the cost of land acquisition may already be prohibitive? In addition, cooperation and communication among biologists in the Northeast are urgently needed to prevent the duplication of research efforts and to disseminate information on current harrier protection efforts (Serrentino 1992). RESEARCH NEEDS:

Determine the amount and type of disturbances that breeding harriers will tolerate, especially for populations located in coastal areas with high human densities (Serrentino and England 1989).

Investigate the relationship between wintering distribution and abundance in coastal Massachusetts, Rhode Island, and Connecticut, and the decline or lack of breeding birds in these same areas.

Determine the effect of saltmarsh ditching on populations and their major prey species (Serrentino and England 1989).

Collect data on hunting habitat and roost site selection in various habitats such as saltmarshes, freshwater wetlands, agricultural habitats, and maritime heaths.

Conduct analyses of pellets and prey remains found at roost sites to determine the prey selection of nonbreeding harriers.

Determine the causes of breeding failure and mortality in young and adults.

Monitor the current levels of biocides and compare with the results of previous studies.

Determine the sizes of hunting ranges of birds during the breeding and nonbreeding season at sites with varying densities and habitat types.

Implement accurate and standardized survey methods to determine the population trends on a regional level. Currently, the status of most populations in the Northeast is unknown because of the lack of reliable estimates of their abundance.

Conduct studies on the techniques used to maintain early successional habitats. Comparisons between treatments and the cost-effectiveness of each treatment are especially needed.

Biological Research Needs: Some important research needs include the following: Determine the extent of breeding range (MacWhirter and Bildstein 1996). Research tolerance to disturbances, especially for populations located in coastal areas with high human densities (Serrentino and England 1989). Investigate the relationship between wintering distribution and abundance and the decline of breeding birds in coastal Massachusetts, Rhode Island, and Connecticut. Determine the effect of saltmarsh ditching on populations and their primary prey (Serrentino and England 1989). Collect data on hunting habitat and roost site selection in various habitats such as saltmarshes, freshwater wetlands, agricultural habitats, and maritime heaths. Conduct analyses of pellets and prey remains found at roost sites to determine the prey selection of nonbreeding harriers. Determine the causes of breeding failure and mortality in young and adults. Monitor the current levels of biocides and compare with the results of previous studies. Conduct studies on the techniques used to maintain early successional habitats; compare treatments and the cost-effectiveness of each treatment.
Population/Occurrence Delineation
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Group Name: Hawks and Falcons

Use Class: Breeding
Subtype(s): Feeding Area, Nest Site
Minimum Criteria for an Occurrence: Evidence of historical breeding, or current and likely recurring breeding, at a given location, minimally a reliable observation of one or more breeding pairs in appropriate habitat. Be cautious about creating EOs for observations that may represent single breeding events outside the normal breeding distribution.
Mapping Guidance: If nest site is separated from feeding area by more than 100 meters, map as separate polygons.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 10 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Separation distance a compromise between usually relatively small home ranges and obvious mobility of these birds. Home ranges variable, ranging from about 0.5 to about 90 square kilometers; the latter figure refers to nests where birds commuted some distance to feeding grounds. A number of studies give mean home ranges on the order of 7 square kilometers, which equates to a circle with a diameter of about 3 kilometers; three times that home range gives a separation distance of about 10 kilometers. Home ranges: Ferruginous Hawk, mean 5.9 square kilometers in Utah (Smith and Murphy 1973); range 2.4 to 21.7 square kilometers, mean 7.0 square kilometers in Idaho (Olendorff 1993); mean 7.6 square kilometers in Idaho (McAnnis 1990); mean 90 square kilometers in Washington (Leary et al. 1998); Red-tailed Hawk, most forage within 3 kilometers of nest (Kochert 1986); mean spring and summer male home ranges 148 hectares (Petersen 1979); Hawaiian Hawk, 48 to 608 hectares (n = 16; Clarkson and Laniawe 2000); Zone-tailed Hawk, little information, apparent home range 1-2 kilometers/pair in west Texas (Johnson et al. 2000); White tailed Kite, rarely hunts more than 0.8 kilometers from nest (Hawbecker 1942); Prairie Falcon, 26 square kilometers in Wyoming (Craighead and Craighead 1956), 59 to 314 square kilometers (reported by Steenhof 1998); Aplomado Falcon, 2.6 to 9.0 square kilometers (n = 5, Hector 1988), 3.3 to 21.4 square kilometers (n = 10, Montoya et al. 1997). Nest site fidelity: high in Zone-tailed Hawk; all seven west Texas nesting territories occupied in 1975 were reused in 1976 (Matteson and Riley 1981). Swainson's Hawk: In California, dispersal distances from natal sites to subsequent breeding sites ranged from 0 to 18 kilometers, mean 8.8 kilometers (Woodbridge et al. 1995); in contrast, none of 697 nestlings in Saskatchewan returned to the study area; three were found 190, 200 and 310 kilometers away (Houston and Schmutz 1995).
Inferred Minimum Extent of Habitat Use (when actual extent is unknown): 3 km
Inferred Minimum Extent Justification: Foraging range variable; 3 kilometers is the mean diameter in several species.
Date: 13Mar2001
Author: Cannings, S.

Use Class: Nonbreeding
Subtype(s): Foraging area, Roosting area
Minimum Criteria for an Occurrence: Evidence of recurring presence of wintering birds (including historical); and potential recurring presence at a given location, usually minimally a reliable observation of 5 birds (this can be reduced to 1 individual for rarer species). Occurrences should be locations where the species is resident for some time during the appropriate season; it is preferable to have observations documenting presence over at least 20 days annually. Be cautious about creating EOs for observations that may represent single events.
Separation Barriers: None.
Separation Distance for Unsuitable Habitat: 10 km
Separation Distance for Suitable Habitat: 10 km
Separation Justification: Separation distance somewhat arbitrary; set at 10 kilometers to define occurrences of managable size for conservation purposes. However, occurrences defined primarily on the basis of areas supporting concentrations of foraging birds, rather than on the basis of distinct populations.
Date: 15Apr2002
Author: Cannings, S.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 03Jan2008
NatureServe Conservation Status Factors Author: Schneider, K., & G. Hammerson
Management Information Edition Date: 01Jun1992
Management Information Edition Author: SERRENTINO, P.; REVISIONS BY K. SCHNEIDER, G. HAMMERSON, M. KOENEN, AND D.W. MEHLMAN
Management Information Acknowledgments: Parts of this abstract were originally published by the U.S. Fish and Wildlife Service in Schneider and Pence (1992). Funding for the preparation of the original document was made possible by the U.S. Fish and Wildlife Service, Newton Corner, MA. K. Bildstein, M. England, and K. Schneider for their commented on an earlier draft of the report. M. England, S. Melvin and R. Tate offered helpful discussions on various management issues. S. Droege answered questions concerning BBS data. A special thanks to A. Haro for his patience and valuable suggestions.
Element Ecology & Life History Edition Date: 01May1995
Element Ecology & Life History Author(s): HAMMERSON, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Amar, A. and S. M. Redpath. 2005. Habitat use by Hen Harriers Circus cyaneus on Orkney: implications of land-use change for this declining population. Ibis 147: 37-47.

  • American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.

  • American Ornithologists' Union (AOU). 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C. [as modified by subsequent supplements and corrections published in The Auk]. Also available online: http://www.aou.org/.

  • American Ornithologists' Union (AOU). Chesser, R.T., K.J. Burns, C. Cicero, J.L. Dunn, A.W. Kratter, I.J. Lovette, P.C. Rasmussen, J.V. Remsen, Jr., J.D. Rising, D.F. Stotz, and K. Winker. 2017. Fifty-eighth Supplement to the American Ornithologists' Union Check-list of North American Birds. The Auk 134:751-773.

  • Anderson, D. W., and J. J. Hickey. 1974. Eggshell changes in raptors from the Baltic region. Oikos 25:395-401.

  • Anderson, R. C., and R. S. Freeman. 1969. Cardiofilaria inornata (Anderson, 1956) from woodcock with a review of Cardiofilaria and related genera (Nematoda: Filarioidea). Trans. Amer. Microsc. Soc. 88:68-79.

  • Andrle, R. F., and J. R. Carrol, editors. 1988. The atlas of breeding birds in New York State. Cornell Univ., Ithaca, New York. 551 pp.

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