Circus cyaneusnorthern harrier(Also: hen harrier; marsh hawk)

Geographic Range

Northern harriers are found throughout the northern hemisphere. In the Americas they breed throughout North America from Alaska and Canadian provinces south of tundra regions south as far as Baja California, New Mexico, Texas, Kansas, and North Carolina. They are only rarely seen breeding in parts of the Atlantic coastal states, such as Vermont, Rhode Island, and Maine and are similarly rare in the arid and mountainous western interior, including most of California, Oregon, and Washington. Their winter range is from southern Canada to the Caribbean and Central America. (Macwhirter and Bildstein, 1996)

In the Palearctic, northern harriers breed throughout Eurasia, from Portugal in the west, to Lapland and Siberia in the north, and east through China. They winter in northern African and tropical Asia. (Macwhirter and Bildstein, 1996)

Habitat

Northern harriers are found mainly in open habitats such as fields, savannas, meadows, marshes, upland prairies, and desert steppe. They also occur in agricultural areas and riparian zones. Densest populations are found in large expanses of undisturbed, open habitats with dense, low vegetation. In eastern North America northern harriers are found most frequently in wetland habitats. In western North America they are most abundant in upland habitats such as desert steppe. Northern harriers avoid forested and mountainous areas. (Eastman, 1999; Macwhirter and Bildstein, 1996; Wheeler and Clark, 1987)

Physical Description

Northern harriers have several characteristics which distinguish them from other birds. Specialized feathers around their face in the shape of a disk focus sound into their ears. Their wings form a dihedral when in gliding flight, and they have a distinctive white rump patch which is obvious during flight. (Wheeler and Clark, 1987)

Adult harriers have yellow eyes. Adult males are gray on their dorsal side. Ventrally, they are white, except for spots on their chest, and black wingtips. Adult females are a brown color, except for underneath their wings, where there are white stripes. Immature males and females resemble the adult female, but they have a darker shade of brown covering the dorsal side and a brownish rusty color underneath. Immature harriers have brown eyes. (Wheeler and Clark, 1987)

The length of adult males varies between 41 and 45 cm (16 to 18 in). The length of adult females varies between 45 and 50 cm (18 to 20 in). Typically the wingspan of adult males varies between 97 and 109 cm (38 to 43 in). The wingspan of adult females varies between 111 and 122 cm (44 to 48 in). The weight of adult males is approximately 290 to 390 grams(1/2 to 1 lb). The average weight of adult females is approximately 390 to 600 grams(1 to 1.3lbs). (Wheeler and Clark 1995,Weidensaul 1996,Ryser 1985,Wheeler and Clark 1987) (Wheeler and Clark, 1987)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range mass
    290 to 600 g
    10.22 to 21.15 oz
  • Range length
    41 to 50 cm
    16.14 to 19.69 in
  • Range wingspan
    340 to 384 mm
    13.39 to 15.12 in

Reproduction

Adult males show interesting behaviors during mating season. During mating season the male courts the female by flying high in the air and then dives down twirling and spinning. Males are sometimes polygynous and have 1 to 3 mates. During incubation the male provides food for the female, but he doesn't approach the nest. When he is near the nest he will call out, and as she comes to him he drops the food to her. During the breeding season northern harriers become very territorial and will attack other hawks, birds, or humans that approach their nesting areas. (Burton and Burton, 1989; Chinery, 1992; Eastman, 1999; Ryser, 1985)

Most males are monogamous, although some males are polygynous, having been known to pair with up to five mates in a season. Females are monogamous. This is due, not only to the female-biased sex ratio, but also to the abundance of food during the spring. (Macwhirter and Bildstein, 1996)

Harriers often nest in loose colonies of 15 to 20 individuals. The nest, built mostly by the female, is made out of sticks and padded on the inside with grass. The nest is built on the ground, often on raised mounds of dirt or clumps of vegetation. (Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; 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Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987; Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987)

Eggs are laid from mid-May to early June. They are white with a blue tint, and occasionally have brown spots. The eggs are approximately 47 x 36mm. Three to five eggs are laid, and incubation is only by the female. (Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987)

The eggs hatch in approximately 31 to 32 days. Male harriers will contribute to the feeding of their offspring during the time they are in the nest and will watch over the nest for a maximum of 5 minutes when the female is away. (Baicich and Harrison, 1997; Burton and Burton, 1989; Eastman, 1999; Terres, 1980; Wheeler and Clark, 1987)

  • Breeding interval
    Northern harriers breed once per season.
  • Breeding season
    Primary females breed from April through July, while secondary females breed from May through September.
  • Range eggs per season
    3 to 5
  • Average eggs per season
    4.4
  • Average eggs per season
    5
    AnAge
  • Range time to hatching
    28 to 36 days
  • Range fledging age
    30 to 35 days
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    3 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

Female investment in her offspring begins with the provisioning of yolk to her eggs. After laying, the female will spread her wings to shelter her young from rain and extreme sun. Her mate will provide food for her for about two weeks after the eggs hatch, then departs. Food is transferred to the female via the male by aerial-pass, and then the female feeds her young. When young reach fledgling stage and are able to fly sufficiently well, food transfer is made to them by their mother, also via aerial-pass. (Macwhirter and Bildstein, 1996; Macwhirter and Bildstein, 1996; Macwhirter and Bildstein, 1996)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

There is very little information known concerning the lifespan of northern harriers. The longest lifespan reported is 16 years and 5 months. The average lifespan, however, is 16.6 months. The oldest reported breeding female was 8 years old.

  • Range lifespan
    Status: wild
    16.19 (high) years
  • Average lifespan
    Status: wild
    16.6 months
  • Average lifespan
    Status: wild
    197 months
    Bird Banding Laboratory

Behavior

Besides flying, northern harriers walk and hop. They use this method of locomotion while retrieving prey, collecting nesting materials, and retrieving nestlings that have strayed from the nest. (Macwhirter and Bildstein, 1996; Macwhirter and Bildstein, 1996)

Harriers typically fly slow and low to the ground, gliding often, and sometimes seeming to hover. They occasionally soar. Males fly faster and are more agile in flight than either females or juveniles and have been seen overtaking prairie falcons. (Macwhirter and Bildstein, 1996; Macwhirter and Bildstein, 1996)

Northern harriers may nest alone or in loose assemblages. Territorial behavior is minimal especially during the breeding season, except at the nest site where both males and females will defend their territory against conspecific intruders. In winter, however, females aggressively exclude males from prime feeding territories. Despite this strong territoriality on the part of females, individuals of both sexes roost on the ground communally during the non-breeding season. During migration, northern harriers, like other raptors, prefer not to fly over open water. (Macwhirter and Bildstein, 1996)

Northern harriers are active during the day and spend much of their time hunting.

  • Range territory size
    1.7 to 150 km^2

Home Range

During breeding season both sexes tend to be territorial around the nests, but otherwise, home ranges tend to overlap. Monogamous male territories tend to be approximately 260 ha (2.6 km square) in size, ranging from 170 (1.7 km square) to 15,000 (150 km square) ha. (Macwhirter and Bildstein, 1996)<