Northern Harrier Life History

Habitat

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.Back to top

Food

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.Back to top

Nesting

Nest Placement

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.

Nest Description

Males sometimes start building a nest platform and the female finishes it. Later, both sexes bring in nesting material but the female takes charge of arranging them to form the nest. The nest platform is made with thick-stalked plants like cattails, alders, and willows. The inner lining uses grasses, sedges, and rushes. Nest building takes 1–2 weeks. The outside of the nest measures 16–24 inches wide by 1.5–8 inches high, while the interior is 8–10 inches wide by 2–4 inches deep.

Nesting Facts

Behavior

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.Back to top

Conservation

Northern Harriers are fairly common, but their populations are declining. From 1966 to 2019, the North American Breeding Bird Survey records a steady decline of over 1% per year, resulting in a cumulative loss of about 34%. Partners in Flight estimates the global breeding population at 820,000 and rates them 11 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. 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 from 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

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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