The genus Circus is a cosmopolitan genus of about ten species. They are medium-sized, slender hawks, the female being considerably larger than the male. They are characterised by long, narrow, rounded tails, small beaks and long, slender legs. The most notable characteristic is the owl-like ruff of facial feathers that cover unusually large ear openings – an adaptation not for low-light hunting, but to locate prey by their rustling and squeaking in tall grasses.
Female averages larger, dark brown above, pale below with dark streaks, from below, dark bands on primaries, secondaries and rectrices.
Juvenile very similar to female, but slightly darker above and ore rufous below. Race hudsonius has rusty markings on underparts.
Listen to the sound of Northern Harrier
Copyright remark: Most sounds derived from xeno-canto
|wingspan min.:||97||cm||wingspan max.:||118||cm|
|size min.:||45||cm||size max.:||55||cm|
|incubation min.:||29||days||incubation max.:||39||days|
|fledging min.:||32||days||fledging max.:||39||days|
Aerial displays and courtship-feeding rates appear to be the principal factors in a female’s selection of a mate. Females sometimes abandon their mates during nestbuilding or courtship if the male fails to display enough or does not provide sufficient food. Males and females do not mate for life. Males usually return to the breeding grounds before females and begin aerial displays when the females arrive. “Sky-Dancing” is intense and more frequent in years when food is abundant, and males that display the most typically attract the largest number of females. Sky-Dancing involves a series of U-shaped, undulating flights at heights that range from 10 meters to 300 meters above the surrounding countryside, and that sometimes cover distances up to a kilometer or more. Males fly to potential nest sites at the end of their display, and interested females follow them. Although they often return to and nest in the same general area, Hen Harriers do not reuse the same nest site year after year.
Harriers build their nests on the ground, almost always in open habitats. Either the male or the female selects the site and both help build the nest. Most nests are placed in areas of dense grassy or shrubby vegetation, and frequently in wet areas, to reduce the risk of predation. Nest construction takes from several days to several weeks. Pairs continue to add nesting material during incubation and, sometimes, until the nestlings are three to four weeks old.
Harriers lay one clutch of four to six eggs annually. Replacement clutches are sometimes laid if the first clutch is destroyed. Incubation begins after the first egg is laid, and the nestlings hatch asynchronously. During the 30- to 32-day incubation period, the female tends the nest continually, leaving only to receive prey deliveries from the male, collect additional nesting material, and take short “exercise” flights. Nestlings are brooded continually for the first 12 to 14 days. Thereafter, the female spends less time at the nest during the day, but continues to brood the young at night for another two weeks. The male provides food to the female when she is at the nest. Males call as they approach the nest with prey and then pass the prey to the female in an aerial transfer. When the female is not at the nest, males sometimes drop food onto the nest, but they do not directly feed the young. Females mated to polygamous males typically receive less food from their mates than their monogamous counterparts, and such females often begin hunting earlier in the nestling period. As a result, nestlings in “polygamous” nests are more susceptible to predation.
By the time the nestlings are two weeks old, they begin to walk and hop up to 15 meters from the nest. Young harriers take their first, short flights when they are four to five weeks of age. After fledging, the young typically roost near each other at night and spend most of their day on perches waiting for their parents to return with food. Siblings often fly together and chase each other, particularly when the adults return to the nest with prey. Parents transfer prey to their young in the air, and the first fledgling to intercept the returning parent usually receives the food. Parents continue to provide the fledglings with food for two to four weeks after fledging. Fledglings spend less than an hour each day hunting, and they seldom catch prey on their own before becoming independent.
The harrier’s owl-like facial ruff and tendency to fly close to the ground allows the species to hear, as well as see, potential prey, and the species often locates its prey by sound. Adult males tend to be the most successful hunters, followed by adult females.
Juveniles are decidedly less proficient hunters than adults. In summer, harriers feed on small- to medium-sized mammals (particularly rodents), as well as on birds, reptiles, amphibians, and insects. Mammals and birds comprise the majority of the species’ diet in winter, but the diets of individuals vary depending upon their location. In the northern portion of their range, voles comprise the majority of the Northern Harrier’s diet. Large prey are usually torn apart before being eaten. Small prey, including mice and insects, sometimes are swallowed whole. Harriers sometimes hide, or cache, surplus food, particularly during the breeding season
Video Northern Harrier
copyright: Don DesJardin
This harrier inhabits a great diversity of open habitats in North America, South America and a large part of Eurasia, from the British Isles to Kamchatka. Its southern populations are sedentary. Those of the north-east of the continent are wintering in the south-west. The total population of the European Union amounts to about 4400 breeding pairs (EBCC Atlas of European Breeding Birds). In some areas it is slightly increasing, but overall it is decreasing.