Northern Harrier – Circus Cyaneus

From a considerable distance, the Northern Harrier is distinctive. It is the  slim, long-tailed hawk gliding low, seeking prey. It holds its wings in a V-shape and has a white patch at the base of its tail. Up close, its face is positively owlish, with prominent ears that assist it in detecting mice beneath vegetation.
Also known as “marsh hawks” or “hen harriers,” northern Harriers breed throughout the northern parts of the northern hemisphere in Canada and the northernmost USA, on moorland, bogs, prairies, farmland coastal prairies, marshes, grasslands, swamps and other assorted open areas. They sojourn south for the winter, bringing some of them to Southern California and San Bernardino County.
The northern harrier is 16 to 20 inches in length with a 38 to 48 inch wingspan. It resembles other harriers in having distinct male and female plumages. The tail is 7.6 to 10.2 inches and the tarsus is 2.8 to 3.5 inches. harriers are relatively long winged and long tailed, having the longest wing and tail relative to body size of any raptors in North America.
The promiscuous gray-and-white males will mate with several females, which are larger and brown. Juveniles are brown above and plain orange-brown below.
The sexes also differ in weight, with males weighing 10 to 14 oz, with an average of 12 oz, and females weighing 14 to 26 oz, with an average of 19 oz.
The female gives a whistled piih-eh when receiving food from the male, and her alarm call is chit-it-it-it-it-et-it. The male calls chek-chek-chek, with a more bouncing chuk-uk-uk-uk during his display flight.
These  raptors  build  nests of sticks lined inside with grass and leaves on the ground or on a mound of dirt or vegetation. Two to ten exceptionally whitish eggs are laid, which measure  approximately 1.9 in × 1.4 in. These are the only hawk-like bird known to practice polygyny – one male mates with several females. When incubating eggs, the female sits on the nest while the male hunts and brings food to her and the chicks. Up to five females have been known to mate with one male in a season. A male will maintain a territory averaging one square mile, though male territories have ranged from 0.66 to 57.92 square miles. The eggs are incubated mostly by the female for 31 to 32 days. The male will help feed chicks after they hatch, but doesn’t usually watch them for a greater period of time than around 5 minutes. The male usually passes off food to the female, which she then feeds to the young, although later the female will capture food and simply drop into the nest for her nestlings to eat. The chicks fledge at around 36 days old, though breeding maturity isn’t reached until 2 years in females and 3 years in males.
As noted, in hunting these harriers will hunt with their wings held in a shallow V in  low flight during which the bird closely hugs the contours of the land below. Northern harriers hunt primarily small mammals, as do most harriers. Preferred prey species can include voles, cotton rats and ground squirrels. Up to 95% of the diet is comprised by small mammals. However birds are hunted with some regularity as well, especially by males. Preferred avian prey include passerines of open country (i.e. sparrows, larks, pipits), small shorebirds and the young of waterfowl and galliforms. Supplementing the diet occasionally are amphibians (especially frogs), reptiles and insects (especially orthopterans). Larger prey, such as rabbits and adult ducks are taken sometimes and harriers have been known to subdue these by drowning them underwater. Harriers hunt by surprising prey while flying low to the ground in open areas, as they drift low over fields and moors. The harriers circle an area several times listening and looking for prey. Harriers use their superior hearing regularly to find prey, This harrier tends to be a very vocal bird while it glides over its hunting ground.
The longest lived known northern harrier is 16 years and 5 months.Adults rarely live more than eight years. Early mortality mainly results from predation. Predators of eggs and nestlings include raccoons, skunks, badgers, foxes, crows and ravens, dogs and owls. Fledgings are also predated regularly, especially by great horned owls. Both parents attack potential predators with alarm calls and striking with talons. Short-eared owls are natural enemies of this species that favor the same prey and habitat, as well as having a similarly broad distribution. Occasionally, both harriers and Short-eared Owls will harass each other until the victim drops its prey and it can be stolen, a practice known as kleptoparasitism. Most commonly, the harriers are the aggressors pirating prey from owls.

Leave a Reply