• Organism

Harrier

The northern harrier and hen harrier are two birds of prey in the harrier subfamily. Some scientists consider them distinct species, while others view them as conspecific (same species).

Overview.

Status: Least-concern
Scientific name: Hen Harrier: Circus cyaneus, Northern Harrier: Circus hudsonius
Average weight: Male: 350g, Female: 530g
Average Size: 16–20 in (length), 38-48 in (wingspan)
Habitat: Open grasslands
Diet: Small birds/mammals

The Northern Harrier breeds in Canada and northern USA, and then migrates to southern USA, Mexico and Central America. The Hen Harrier breeds across Eurasia, wintering in Western Europe and Central Asia. Harriers will breed on moorland, prairies, marshes, grasslands, swamps and other open areas, and males can have territories ranging from 1.7 to 150 sq km.

As birds of prey, harriers will hunt along open areas by quartering fields and use their vision and hearing to detect prey. Preferred prey includes small birds (swallows, larks, young waterfowl) and mammals (squirrels, voles), but they will also supplement their diet with insects, frogs and reptiles. Once captured, they eat their prey on the ground or from perches on low trees or posts.

Harriers are known for being one of the few raptors to engage in polygamy, with a male being able to mate with up to five females in one breeding season. Nests built out of sticks and lined with grass and leaves are set up on mounds, and the female will incubate eggs in them for around a month until they hatch. Both the female and male will help bring food to the chicks until 36 days when they fledge.

Scientific significance.

Birds of prey are a group of birds that are often persecuted. Conflicts often arise if their natural diet is ‘farmed’ on private areas such as grouse moorland, fish stock lakes, poultry farms, etc. Though illegal, poisoning of birds of prey is so commonplace that important populations have all but vanished in many regions.

It is important to understand the diversity, habits, behaviour and ecosystems of species to truly understand how changes in the environment will affect their survival.

Conservation.

Harriers are classified as Least Concern by the IUCN, and in most countries aren’t undergoing severe population decline. An exception is the UK, where the hen harrier was hunted to extinction on mainland Britain in the 19th century. Whilst it made a comeback in the 20th century, it has remained vulnerable and its population has declined throughout the UK.

This has resulted in it becoming the target of conservation programmes, with there only being 4 breeding pairs in England in 2016. Breeding pairs in Scotland fell from 505 to 460 between 2010-2016, while in Wales they declined from 57 to 35 pairs and 59 to 46 pairs in Northern Ireland. This decline has been attributed to habitat loss and the illegal killings of harriers; conservation efforts have conflicted with gamekeepers who rear grouse on moorlands and often illegally set poison traps for birds of prey.

What Earlham Institute is doing.

The Earlham Institute have recently published research on the evolution of Hen and Northern Harriers, resulting in the two populations being reassigned as separate species.

Learn more.

More information can be found at All About Birds.

If you’re interesting in learning more about British conservation efforts for the hen harrier, then you can read about it on the RSPB.

Related reading.