Circus cyaneus

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.

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.

• Biogeographic Regions
• nearctic nearctic
  • native native
• palearctic palearctic
  • native native
• oriental oriental
  • native native

• Other Geographic Terms
• holarctic holarctic

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.

• Habitat Regions
• temperate temperate
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• chaparral chaparral

• Wetlands
• marsh marsh

• Other Habitat Features
• agricultural agricultural
• riparian riparian

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.

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.

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)

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes colored or patterned differently

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.

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.

• Mating System
• monogamous monogamous
• polygynous polygynous

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.

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.

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.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

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.

• Parental Investment
• altricial 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.

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.

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 .

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.

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

• Key Behaviors
• flies
• glides
• diurnal diurnal
• motile motile
• migratory migratory

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.

Communication and Perception

Northern harriers are especially vocal around the nest. Sounds of courtship are reflected by rapid kek, quik, or ek notes in series. Calls of distress are urgent and high pitched, also in rapid succession. This call is more nasal-sounding in males than in females.

There also exists a "food call", which is observed most frequently during breeding season. Females issue a piercing eeyah, eeyah scream, which may be repeated for several minutes. This is responded to by a barely audible purrduk chuckle by the male, which solicits the female from the nest.

Young harriers emit a "begging call" when they hear their parents or in response to seeing their parents fly overhead. This sound is often referred to as a pain call, and it is a series of chit notes. This sound only becomes more emphatic with increasing age.

Northern harriers, like most raptors, have a keen sense of vision. Northern harriers are unusual in that their owl-like facial ruff enhances their sense of hearing, which they use extensively in finding prey.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

The diet is variable, depending on dominant prey types in the area. In areas with large populations of small mammals, they make up 95% of the diet. In northern grasslands, the diet may be almost exclusively Microtus voles. Northern harriers also eat other small vertebrates, including snakes, frogs, passerine birds, and small waterfowl. When hunting for food, harriers glide at a slow pace close to the ground until prey is found. Harriers then dive quickly to capture it. They may also hide in vegetation, waiting to pounce on prey. They sometimes store extra prey to eat later.

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates

• Animal Foods
• birds
• mammals
• amphibians
• reptiles

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Northern harriers have many predators, including raccoons, skunks, American crows, common ravens, coyotes, feral dogs, red foxes, and great horned owls. American crows and common ravens prey on eggs, while other raptors, especially great horned owls, target nestlings.

Northern harriers with young generally respond aggressively to predators. Defense ranges from aggressive distress calls to striking the intruder with closed talons. Males and females contribute equally to defense.

Northern harriers often compete with short eared owls for the same food source. Food shortages can occur because both hunt the same prey. Northern harriers have a tendency to steal prey away from short eared owls by harassing them until the owl drops its prey. Short eared owls have been known to hunt both at night and during the day, while northern harriers hunt only during the day.

Ecosystem Roles

Predation by northern harriers can have significant effects on populations of field mice and other rodents.

As prey, northern harriers provide food for some terrestrial predators, such as coyotes Canis latrans , striped skunks Mephitis mephitis , raccoons Procyon lotor , and red foxes Vulpes vulpes .

Economic Importance for Humans: Positive

Northern harriers help protect crops by reducing populations of field mice and other rodents. Unlike some other hawk species, they do not attack poultry.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

There are no negative affects of northern harriers on humans.

Conservation Status

No conservation measures have been enacted specifically for this species, however, conservation measures for waterfowl and habitat management for game birds has increased local numbers of nesting northern harriers. The species is abundant enough to be rated "Least Concern" by the IUCN. It it protected under the Migratory Bird Treaty, and is listed in Appendix II of CITES.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Lauren Pajerski (editor), Undergraduate Research Opportunity Program, University of Michigan, George Hammond (editor), Animal Diversity Web, Tanya Dewey (editor), Animal Diversity Web.

Brian Limas (author), Fresno City College, Carl Johansson (editor), Fresno City College.

References

Baicich, P., C. Harrison. 1997. A Guide to the Nests, Eggs, and Nestlings of North American Birds . New York City, New York, USA: Academic Press.

Burton, M., R. Burton. 1989. Northern harrier. Pp. 1162 in The Marshall Cavendish International Wildlife Encyclopedia , Vol. 10. Toronto, Canada: Marshall Cavendish Corporation.

Chinery, M. 1992. Pp. 144 in The Kingfisher Illustrated Encyclopedia of Animals . New York: Kingfisher Books.

Dechant, J., M. Sondreal, D. Johnson, L. Igl, C. Goldade. 1998. "Effects of management practices on grassland birds: Northern Harrier.." (On-line). Accessed September 15, 2000 at http://www.npwrc.usgs.gov/resource/literatr/grasbird/harrier/harrier.htm .

Eastman, J. 1999. Birds of Lake, Pond, and Marsh . Pennsylvania, USA: Stackpole Books.

Macwhirter, R., K. Bildstein. 1996. Northern Harrier. The Birds of North America , 210: 1-25.

Ryser, F. 1985. Birds of the Great Basin- A Natural History . Reno, Las Vegas: University of Nevada Press.

Snyder, N., H. Snyder. 1991. Birds of Prey- Natural History and Conservation of North American Raptors . MN.: Voyageur Press Inc..

Terres, J. 1980. Pp. 483 in The Audubon Society Encyclopedia of North American Birds . New York: Alfred A.Knoph Inc..

Weidensaul, S. 1996. Raptors-The Birds of Prey . New York: Lyons and Burford.

Wheeler, B., W. Clark. 1995. A Photographic Guide to North American Raptors . San Diego: Academic Press Inc..

Wheeler, B., W. Clark. 1987. The Peterson Field Guide Series- A Field Guide to Hawks of North America . Boston: Houghton Mifflin Company.