Habitat

Grassland

Breeding Northern Harriers are most common in large, undisturbed tracts of wetlands and grasslands with low, thick vegetation. They breed in freshwater and brackish marshes, lightly grazed meadows, old fields, tundra, dry upland prairies, drained marshlands, high-desert shrubsteppe, and riverside woodlands across Canada and the northern United States. Western populations tend to breed in dry upland habitats, while northeastern and Midwestern populations tend to breed in wetlands. During winter they use a range of habitats with low vegetation, including deserts, coastal sand dunes, pasturelands, croplands, dry plains, grasslands, old fields, estuaries, open floodplains, and marshes.

Food

Mammals

Northern Harriers forage on the wing, coursing low over the ground. Unlike other hawks, they rely heavily on their sense of hearing to capture prey. In the breeding season they eat small mammals, reptiles, amphibians, and birds. During winter, harriers in the northern part of the range feed almost exclusively on meadow voles; they also eat deer mice, house mice, shrews, rabbits, and songbirds (including meadowlarks, Northern Cardinals, and Song Sparrows). Harriers wintering in the southern part of their range eat cotton rats, house mice, harvest mice, rice rats, shrews, and songbirds.

Nesting

Nest Placement

Ground

Either the male or the female chooses the nest site, which is on the ground and usually in a dense clump of vegetation such as willows, grasses, sedges, reeds, bulrushes, and cattails.

Behavior

Soaring

Northern Harriers usually fly slowly and low over the ground, their wings held in a V-shape as they glide. Most males have either one mate or two mates at a time, but some have up to five mates when food is abundant. Each male courts females and advertises his territory by performing sky-dancing displays: undulating, rollercoaster-like flights up to 1,000 feet off the ground, sometimes covering more than half a mile. Although they don’t protect large territories, both males and females vigorously defend the nest itself. Nesting females usually chase away other females, and males chase other males. Females incubate eggs and brood chicks, while males provide most of the food for the females and nestlings. Nest predators include coyotes, feral dogs, striped skunks, raccoons, red foxes, American Crows, Common Ravens, and Great Horned Owls. Livestock and deer sometimes trample eggs and nestlings underfoot. Juvenile harriers play (and hone their hunting skills) by pouncing on inanimate objects like vole-sized corncobs. In winter, Northern Harriers roost in groups on the ground, sometimes with Short-eared Owls. The larger females are dominant to the males.

Conservation

Least Concern

Northern Harriers are fairly common, but their populations are declining. The North American Breeding Bird Survey records a steady decline of 0.8 percent per year from 1966 to 2010, with Canadian populations declining more than U.S. populations. Partners in Flight estimates there are about 1.4 million Northern Harriers in the world, with 35 percent of the population in the U.S., 17 percent in Canada, and 10 percent in Mexico. The species is not on the Partners in Flight 2012 Watch List. Habitat loss has contributed to reduced harrier populations as people have drained wetlands, developed land for large-scale agriculture, and allowed old farmland to become reforested. The small mammals that harriers prey upon have been reduced because of overgrazing, pesticides, and reduced shrub cover from crop field expansion. Because they eat small mammals, Northern Harriers are susceptible to the effects of pesticide buildup as well as direct effects by eating poisoned animals. In the mid-twentieth century their populations declined from contamination by DDT and other organochlorine pesticides, but rebounded after DDT restrictions went into effect in the 1970s. Northern Harriers have been mostly safe from hunting because of their reputation for keeping mouse populations in check, but they are still sometimes shot at communal winter roosts in Texas and the southeastern United States.

Credits

• MacWhirter, R. B., and K. L. Bildstein. 1996. Northern Harrier (Circus cyaneus). In The Birds of North America, No. 210 (A. Poole and F. Gill, eds.). The birds of North America Online, Ithaca, New York.
• Partners in Flight. 2012. Species assessment database.
• Sauer, J.R., J.E. Hines, J.E. Fallon, K.L. Pardieck, D.J. Ziolkowski Jr., and W.A. Link. 2011. The North American Breeding Bird Survey, Results and Analysis 1966–2010. Version 12.07.2011. USGS Patuxent Wildlife Research Center, Laurel, MD.
• USGS Patuxent Wildlife Research Center. 2011. Longevity Records of North American Birds.