The Northern Harrier quarters low (generally less than 10 feet [3.1 meters]) over marsh and field, employing an unsteady "tipsy" style of flap and glide flight, utilizing the slightest breezes over rough terrain. It will crisscross natural and man-man-made edges like run-off channels and fences, double-back on its path, and habitually suddenly pull up to hover a few feet above the grass, with long legs dangling, and then may drop into the vegetation to seize prey. This type of flight is most often associated with hunting and is characterized by more than five sharp turns per minute. During migration, the Northern Harrier is capable of direct gliding or flap-and-glide flight, often at high elevations. Occasionally, both during the breeding season and in migration, the bird will soar on thermals with wings and tail spread. The Northern Harrier habitually perches both on the ground and on low perches like posts, stumps, and rocks.
The Northern Harrier hunts all day long, and in some locations show peaks of hunting activity in the early morning and in the hour before dusk. The rate of prey capture diminishes during windy or rainy weather. It cruises low over open ground and upon sighting, or hearing prey, may hover above it, drop pouncing upon it after a few seconds. The crisscross flight path increases the element of surprise in the harrier's flight which would be minimized if the hawk simply flew straight down a ditch or along an embankment. Some authorities differentiate between "quartering" and "border following", the main difference appearing to be that quartering occurs over non-border areas. Borders include the edges of certain vegetative patches, fence lines, ridges, shorelines, and other borders. The male harrier tends to fly lower and faster than females. The harrier also "foot-stabs" to flush prey from cover, lowering a foot into grass while hovering. The harrier also habitually flushes prey to "test" its condition, seldom pursuing large active prey. The harrier's grasp is relatively weak so prey is killed with the beak while the bird feeds. The Northern Harrier has hearing at least four times more acute than other hawks and is able to locate prey by sound alone. The harrier will hunt newly mown fields for uncovered prey, and attend prairie fires and sometimes follow mammal predators such as red foxes, perhaps using the animal as a beater. The harrier will also hunt from the ground, waiting to surprise prey or from a low perch. It occasionally strikes waterfowl on the surface of the water, often snatches ducklings and American Coot chicks, and only rarely takes fish like an Osprey. Occasionally the harrier will feed on carrion.
The Northern Harrier defends home ranges, breeding territories, and winter territories. This species commonly roosts communally within the span of October to April but individuals may defend winter territories distant from their roost. It establishes hunting and nesting territories by the time of egg- laying. Nonbreeders also can establish territories and build dummy nests. Territories vary in size depending upon whether nesting is colonial or solitary. Ditches, windrows, and roads often become territorial boundaries between neighbors. Territorial conflicts are most frequent early in the nesting cycle, and involve aerial chases and talon grappling.
Larger birds like the Ring-necked Pheasant and Greater Prairie Chicken will stand their ground against Northern Harriers. Harriers carrying prey are often mobbed by songbirds. Chases and stoops between harriers and Short-eared Owls are common. Harriers will also rob Short-eared Owls of their prey. Harriers will also attempt to rob other species including Peregrine Falcons and Prairie Falcons, and are robbed themselves by other raptors including the Crested Caracara, Prairie Falcon, Peregrine Falcon, and Bald Eagle. Harriers will also chase other raptors such as Red-tailed and Rough-legged hawks from their home ranges.
The Northern Harrier's primary display is called sky-dancing and is performed mostly by males, though occasionally a female will sky-dance, particularly late in the season. Harriers will sky-dance over marshes even while on migration. Breeding has taken place without sky-dancing; however, this display is a normal part of courtship. The male engages in a series of steep dives and pull ups, or U's, with the bird turning sideways at the apex of each U in a barrel roll. Tumbling may also occur with the diving bird throwing its wings over its back and tumbling like a pigeon as it descends. A male may dive, with beating, with partially retracted wings, or may actually flip over at the crest to start the descent while upside down. Copulation often follows the male presenting food to the female, sometimes in a mid-flight drop. Copulation generally takes place on the ground.
The oldest wild bird lived to be 16 years five months old. Causes of mortality include predation by Great Horned Owls and Red-tailed Hawks, predation of nests by several mammals including racoons, minks, weasels, coyotes, skunks, foxes, and by American Crows, trampling of nests by livestock, destruction of nests by mowing and haying equipment, illegal shooting, and collisions with vehicles. Harriers have also died from fowl cholera and type C botulism probably contracted from contaminated prey.
ADAPTATIONS
The Northern Harrier is the only North American hawk that has evolved an owl-like facial disk. This disk has sound gathering qualities that enable the harrier to hunt prey by sound as well as sight. Tests indicate that the harrier's hearing is at least as acute as that of most North American owls.
The harrier is also unique in its ability to respond to high populations of prey species, such as voles, by becoming a polygamous breeder. Males can have up to seven mates who each build a nest and raise young.
The Northern Harrier also adapts to its environment by diversifying its diet according to seasonal and local abundance of different prey species.
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Oppurtunistic hunter; prefers voles
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Quarters over marsh to find food
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