The northern harrier (Circus hudsonius) is a medium-sized bird of prey belonging to the harrier family (Circidae). It is also known as the hen harrier, marsh hawk, or northern harrier hawk. Some key facts about the northern harrier include:
- It is found throughout North America, parts of South America, and Eurasia.
- Adults have a white rump patch and long, barred tail.
- They hunt small mammals, birds, reptiles, amphibians and insects by flying low over open areas.
- Northern harriers nest on the ground in marshes, grasslands and tundra.
- They are most active at dawn and dusk.
- Some populations migrate, while others are permanent residents.
- They soar with their wings held in a distinctive V-shape.
In this article, we’ll explore the northern harrier in more detail, looking at its taxonomy, physical description, habitat, diet, hunting behavior, reproduction and conservation status.
Taxonomy
The northern harrier belongs to the following taxonomic classification:
- Kingdom: Animalia
- Phylum: Chordata
- Class: Aves
- Order: Accipitriformes
- Family: Accipitridae
- Genus: Circus
- Species: Circus hudsonius
It is one of 11 species within the genus Circus, which are medium-sized harriers characterized by long, broad wings and buoyant flight. The closest relative to the northern harrier is the hen harrier (Circus cyaneus) which occupies the same ecological niche in Eurasia.
Physical Description
The northern harrier is a slender, medium-sized raptor with long, fairly broad wings and a long, rounded tail. Some key physical features include:
- Length: 14-19 inches
- Wingspan: 40-54 inches
- Weight: 7-16 ounces
- Sexual dimorphism – females are larger than males.
- Distinctive white rump patch.
- Long tail with conspicuous black bands.
- Yellow eyes.
- Hooked bill.
- Long legs and toes.
- Males are mostly gray, females are brown.
In flight, northern harriers display a distinctive silhouette, with long wings held in a v-shape. The wings are broader than other hawks relative to their body size, allowing them to fly with slow, graceful wingbeats. The long tail helps provide lift and aids in maneuverability.
Northern harriers have facial discs like owls, indicating their acute sense of hearing. Their eyes are also large and situated to allow a wide field of view. These adaptations help them locate prey while flying low over open areas.
Habitat
Northern harriers occupy a variety of open habitats across North America, including:
- Marshes
- Wetlands
- Grasslands
- Prairies
- Fields
- Moors
- Tundra
- Savannahs
They tend to avoid dense forests and woodlands. Northern harriers generally inhabit areas with tall grasses, rushes and other emergent vegetation. The vegetation provides cover for nesting and roosting. They are commonly found in both freshwater and brackish marshes.
In the western United States, northern harriers occupy drier shrublands and grasslands. They can also be found in agricultural areas during winter, foraging over croplands and pastures.
Northern harriers that breed in Canada and Alaska migrate south in winter to open habitats across the United States and Mexico. Some southern populations are year-round residents.
Diet
Northern harriers are carnivores and eat a varied diet consisting mainly of small mammals, birds, reptiles, amphibians and insects. Their typical prey includes:
- Voles
- Mice
- Shrews
- Rats
- Rabbits
- Snakes
- Lizards
- Frogs
- Small birds
- Insects
They will also opportunistically eat fish, crabs, mollusks and carrion. Harriers hunt mostly during daylight hours, with peak activity in the early morning and late afternoon.
Northern harriers employ a distinctive hunting style, coursing low over open ground while listening for prey. Their facial discs help direct sound to their ears so they can locate prey by sound alone. They rely on stealth and surprise rather than speed when hunting.
When prey is detected, northern harriers abruptly turn or hover momentarily to plunge feet first and grab the prey with their talons. They sometimes pin larger prey to the ground with their feet. Prey is typically consumed on the ground, with indigestible parts regurgitated as pellets.
Hunting Behavior
Northern harriers have a very distinctive hunting behavior characterized by low, coursing flights over open habitats:
- They fly with wings held in a dihedral or v-shape rther than flat like most hawks.
- Legs are often lowered to hang beneath the body while flying.
- Flap-flap-glide style of flying with slow, deep wingbeats.
- They fly low, typically less than 3 feet off the ground.
- Harriers mainly hunt by sound, using their acute hearing.
- They frequently hover into the wind and plunge feet-first to catch prey.
- Most hunting occurs during dawn and dusk.
- Hunting flights average 15-20 minutes.
Northern harriers coursing low over the landscape are a distinctive sight. Their flight style allows them to hunt by ear and spot prey moving in grass and vegetation. The slow flight and v-shaped wings provide good maneuverability and lift at low speeds.
Male and female northern harriers often hunt together during breeding season, with one bird flushing prey towards its mate. During winter migrations and at wintering grounds, northern harriers occasionally hunt in loose groups, coordinating to increase prey captures.
Young harriers go through an extended fledgling period, during which adults train them to hunt effectively. Juveniles initially make short practice flights and are fed by parents, eventually progressing to longer flights and independent hunting.
Reproduction
Northern harriers breed between April and July, with the timing synchronized to match peak prey availability:
- Courtship: Spectacular aerial displays including loop-de-loops, spirals and food transfers.
- Nest: Built on ground in marsh vegetation, grasses or shrubs. Sticks lined with grasses.
- Eggs: Clutch of 4-6 dull white/blue eggs. Incubation lasts 31-38 days.
- Young: Precocial, covered in white down. Fledge after 30-40 days.
- Fledging: Juveniles dependent on parents for several weeks after fledging.
Nests are built solely by females, usually close to foraging areas with tall cover and concealment. Males pass food to females during courtship and deliver most food to nest and young.
Young fledge at 4-5 weeks but remain close to nest and adults. They make increasingly longer practice flights to build stamina and hunting skills. Juveniles become independent at 10-11 weeks old.
Northern harriers can breed at one year old. They are usually monogamous within breeding seasons but may choose new mates in subsequent years. Average lifespan in the wild is 12 years.
Migration
Northern harrier populations exhibit a variety of migratory strategies:
- Northernmost breeders are long-distance migrants, wintering to the south.
- Birds at mid-latitudes are medium-distance migrants.
- Southern populations may be year-round residents.
- Males begin fall migration before females and juveniles.
- Spring migration peaks in March through May.
- Males arrive at breeding sites first to establish territories.
Northern harriers breeding in Canada and Alaska migrate south into the United States and Mexico for winter. Some winter as far south as northern South America.
At more southern latitudes, northern harriers may migrate shorter distances or be permanent residents. There is evidence that juveniles disperse farther distances than adults.
Migratory populations complete their spring migration by May to establish breeding territories early. Males arrive before females to display and defend nesting sites.
Conservation Status
According to the International Union for Conservation of Nature (IUCN), the northern harrier has a global conservation ranking of Least Concern:
- Still has a large global population and range.
- Population trend currently appears to be stable.
- Does adapt well to agricultural areas and some human disturbance.
- Has declined in some regions from habitat loss and chemical use.
- Loss of native grasslands and wetlands is an ongoing threat.
In portions of its range, the northern harrier has seen population declines linked to:
- Drainage of wetlands
- Conversion of grasslands for agriculture
- Declines in small mammal populations
- Increased pesticide use reducing prey
- Disturbance of nesting habitats
Conservation actions needed to sustain northern harrier populations include:
- Protection of remaining grasslands and wetlands
- Sustainable agricultural practices
- Limits on chemical use
- Prevention of disturbances around nest sites
- Monitoring populations
While still relatively common, habitat loss does pose long-term threats to northern harrier populations. Preserving suitable breeding and foraging habitats will be key to conservation of this unique raptor species.
Conclusion
In summary, the northern harrier is a distinctive raptor adapted to hunting over open country by coursing low to the ground. Some of its key traits and behaviors include:
- Graceful low flight with wings in a v-shape.
- Acute hearing to locate prey while flying.
- Plunging feet-first to seize prey on the ground.
- Nests on ground in concealed marsh vegetation.
- Migratory populations winter in the southern U.S and Mexico.
- Habitat loss and chemical use pose conservation threats.
The northern harrier’s specialized hunting behavior and role as a wetland and grassland specialist make it a species of conservation concern. Protecting its habitats and monitoring populations will help ensure the marsh hawk continues gliding low over fields and marshes for years to come.
