Northern Harrier Circus hudsonius Scientific name definitions

The Northern Harrier is a slender, white-rumped, and low-flying raptor of tundra, grasslands, weedy agricultural fields, and fresh and saltwater marshes. The only representative in North America of the cosmopolitan genus Circus, the Northern Harrier was until recently considered conspecific with the Hen Harrier (Circus cyaneus) of Eurasia, but differs from that species in genetics and plumage. The Northern Harrier and Hen Harrier are the most northerly breeding Circus species and their degree of sexual dimorphism in plumage and propensity for polygyny are exceptional among birds of prey.

The Northern Harrier nests on the ground, usually in tall, dense clumps of vegetation, either alone or in loose colonies. Most males are monogamous or simultaneously bigamous, although some males pair with up to 5 mates in a season. The frequency of polygyny is influenced more strongly by the abundance of food in spring than by a female-biased sex ratio. Females incubate eggs and brood offspring, and males provide the bulk of food for their mates and nestlings.

Like most other harriers, the Northern Harrier forages on the wing, capturing a wide range of prey, mainly small- and medium-sized mammals and birds, while coursing low and buoyantly over the ground. It frequently relies heavily on auditory cues, as well as visual ones, to capture prey. Annual breeding numbers and productivity are strongly influenced by the availability of this species' principal prey in spring, usually microtine voles. During winter, individuals roost communally on the ground.