Northern harrier (Circus cyaneus)

Also known as: Hen harrier, marsh hawk
  
French: Busard Saint-Martin
KingdomAnimalia
PhylumChordata
ClassAves
OrderFalconiformes
FamilyAccipitridae
GenusCircus (1)
SizeLength: 43 - 52 cm (2)
Wingspan: 99 - 121 cm (2)
Male weight: 290 - 400 g (3)
Female weight: 370 - 708 g (3)

Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (4).

The northern harrier is a slender, medium-sized hawk, with a long tail, wings and legs, a characteristic white rump, and a distinctive ‘facial disc’, which gives it an owl-like appearance (3) (5) (6). The male is grey above and white underneath, with obvious black wing-tips and contrasting yellow legs, eyes and facial skin. The female is larger and is quite different in appearance, being dark brown above, paler below, with dark streaks, and with bars on the wings and tail (3) (5) (7) (8). Juvenile northern harriers resemble the female, but are usually darker above and more reddish-brown below, sometimes without streaking (2) (3) (5) (8). The northern harrier uses a variety of calls, including a long, rapid series of kek notes, a piercing, descending scream, given by the female when soliciting food from the male, and a soft, chuckling call at the nest (5) (6).

The northern harrier is the most northerly breeding and one of the most widespread of all harrier species (9), occurring across much of North America, Europe and Asia. In North America, the subspecies Circus cyaneus hudsonius can be found from Alaska and Canada south to Mexico, wintering as far south as Central or South America and the Caribbean. Circus cyaneus cyaneus occurs throughout Europe and north Asia to Kamchatka, wintering as far south as northern Africa, through southern Asia, to southeast China and Japan (2) (3) (5) (10).

This species inhabits a wide variety of open habitats with low ground cover, including grassland, wetlands and marshland, estuaries, riparian woodland, meadows, moorland, pasture, cropland, scrub, steppe, and semi-desert (2) (3) (5) (8).

Typically hunting from a slow, buoyant flight, usually quite low to the ground, the northern harrier takes a variety of prey, ranging from small mammals and birds to reptiles, amphibians, insects, larger mammals and birds, and sometimes carrion (2) (3) (5) (6). Unlike other hawks, it relies heavily on sound as well as vision to detect prey, aided by the facial disc which, as in owls, is thought to help with the location of faint sounds, allowing the harrier to detect prey concealed in vegetation (3) (5) (6) (8).

The northern harrier commonly perches and even roosts on the ground, and outside of the breeding season often gathers in communal roosts, sometimes numbering tens or even, rarely, hundreds of birds. It also often nests in loose colonies, sometimes practicing an unusual degree of polygyny, with males simultaneously raising several broods with as many as seven different females (2) (3) (5) (6). Breeding usually takes place from April to July (2), the male performing a spectacular aerial ‘sky-dance’ at the start of the season, involving a series of steep climbs and near vertical plunges, with twists, rolls, spirals and loops, accompanied by much calling (3) (6).

The nest is built on the ground, usually in dense clumps of vegetation, and comprises a pile of sticks, grasses, sedges and other materials. Around 3 to 6 eggs are laid, and are incubated by the female for 29 to 31 days. During this time, and until the chicks are about two weeks old, the male brings almost all the food, transferring it to the female in impressive aerial passes, in which the food is dropped by the male and then caught by the female in mid-air (2) (3) (5) (6). The young fledge at 29 to 42 days, and are dependent on the adults for several more weeks. Sexual maturity is reached at around 2 to 3 years, and lifespan may be up to 16 years (2) (3) (5).

The northern harrier still has a large range and a large global population (10), but has been undergoing a decline during the last century, mainly as a result of habitat degradation. In particular, the draining of wetlands, reforestation of farmlands, and intensification of agriculture are thought to have reduced prey availability and nesting sites (2) (5) (6) (11). Illegal persecution is also a problem in some areas, particularly on managed grouse moors, where the northern harrier often predates grouse chicks (2) (5) (11). One study between 1988 and 1995 estimated that, on average, 11 to 15 percent of the breeding female northern harriers in Scotland were killed by humans each year on grouse moors (12). Other threats include organochloride pesticides, thought to reduce eggshell thickness and decrease reproductive success (3) (5).

The northern harrier is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning international trade in the species should be carefully controlled (4). It is also listed on Appendix II of the Convention on Migratory Species (CMS), which aims to conserve migratory species throughout their range (13), and is protected under a range of legislation in Europe (14) (15). No specific conservation measures are reported to be in place in North America, but protection of undisturbed habitats and further study of the species at its winter roosts have been recommended (5).

The scale of illegal killing of northern harriers in Britain has led to a range of initiatives, such as Natural England’s Hen Harrier Recovery Project, which aims to monitor breeding numbers and to address ongoing illegal persecution (11) (16). It is believed that without an end to such persecution, the ability of this unique bird of prey to recover in this and other areas will sadly be severely limited (16).

To find out more about the conservation of the northern harrier see:

For more information on this and other bird species please see:

Authenticated (15/10/09) by Dr Keith L. Bildstein, Sarkis Acopian Director of Conservation Science, Hawk Mountain Sanctuary.
http://www.hawkmountain.org

  1. IUCN Red List (June, 2009)
    http://www.iucnredlist.org
  2. del Hoyo, J., Elliott, A. and Sargatal, J. (1994) Handbook of the Birds of the World. Volume 2: New World Vultures to Guineafowl. Lynx Edicions, Barcelona.
  3. Ferguson-Lees, J. and Christie, D.A. (2001) Raptors of the World. Helm Identification Guides, A & C Black Publishers, London.
  4. CITES (June, 2009)
    http://www.cites.org
  5. Macwhirter, R.B. and Bildstein, K.L. (1996) The Birds of North America Online: Northern Harrier (Circus cyaneus). Cornell Lab of Ornithology, Ithaca. Available at:
    http://bna.birds.cornell.edu/bna/species/210/
  6. Snyder, N. and Snyder, H. (2006) Raptors of North America: Natural History and Conservation. Voyageur Press, Osceola, Wisconsin.
  7. Peterson, R.T., Mountfort, G. and Hollom, P.A.D. (1993) Collins Field Guide: Birds of Britain and Europe. HarperCollins Publishers, London.
  8. The Cornell Lab of Ornithology - All About Birds: Northern Harrier (June, 2009)
    http://www.allaboutbirds.org/guide/Northern_Harrier/id
  9. Bildstein, K.L. (2006) Migrating Raptors of the World: Their Ecology and Conservation. Cornell University Press, Ithaca, New York.
  10. BirdLife International (June, 2009)
    http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3407&m=0
  11. RSPB: Hen Harrier (June, 2009)
    http://www.rspb.org.uk/ourwork/conservation/species/casestudies/henharrier.asp
  12. Etheridge, B., Summers, R.W. and Green, R.E. (1997) The effects of illegal killing and destruction of nests by humans on the population dynamics of the hen harrier Circus cyaneus in Scotland. Journal of Applied Ecology, 34: 1081 - 1105.
  13. Convention on the Conservation of Migratory Species of Wild Animals (June, 2009)
    http://www.cms.int
  14. EC Birds Directive (June, 2009)
    http://www.jncc.gov.uk/page-1373
  15. Council of Europe: Bern Convention (June, 2009)
    http://www.coe.int/t/dg4/cultureheritage/conventions/bern/
  16. Natural England. (2008) A Future for the Hen Harrier in England?. Natural England, Sheffield, UK. Available at:
    http://www.naturalengland.org.uk/Images/hen_harrier_report221208_tcm6-9451.pdf