Hen harrier

Hen harrier
Adult female, American subspecies
Adult male
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Accipitriformes
Family: Accipitridae
Genus: Circus
Species: C. cyaneus
Binomial name
Circus cyaneus
(Linnaeus, 1766)
Range of C. cyaneus      Breeding summer visitor     Breeding resident     Winter visitor
Synonyms

Circus hudsonius

The hen harrier (Circus cyaneus) or northern harrier (in the Americas) is a bird of prey. It breeds throughout the northern parts of the northern hemisphere in Canada and the northernmost USA, and in northern Eurasia. This species is polytypic, with two subspecies. Marsh hawk is a historical name for the American form.[2] The term "hen harrier" refers to its former habit of preying on free-ranging fowl.[3]

It migrates to more southerly areas in winter. Eurasian birds move to southern Europe and southern temperate Asia, and American breeders to the southernmost USA, Mexico, and Central America. In the mildest regions, such as France, Great Britain, and the southern US, hen harriers may be present all year, but the higher ground is largely deserted in winter.

Description

Bird in flight at an altitude over 12,500 ft in Pangolakha Wildlife Sanctuary in East Sikkim district, India in the month of November.
Juvenile flying at Bosque del Apache National Wildlife Refuge, USA
In flight
Adult female flying in California

The hen harrier is 41–52 cm (16–20 in)[2] long with a 97–122 cm (38–48 in) wingspan.[4][5] It resembles other harriers in having distinct male and female plumages. The sexes also differ in weight, with males weighing 290 to 400 g (10 to 14 oz), with an average of 350 g (12 oz), and females weighing 390 to 750 g (14 to 26 oz), with an average of 530 g (19 oz).[2][5] Among standard measurements, the wing chord is 32.8 to 40.6 cm (12.9 to 16.0 in), the tail is 19.3 to 25.8 cm (7.6 to 10.2 in) and the tarsus is 7.1 to 8.9 cm (2.8 to 3.5 in).[5] It is relatively long winged and long tailed, having the longest wing and tail relative to its body size of any raptor occurring in North America.[5]

The male of the nominate race, C. c. cyaneus (Linnaeus, 1766), which breeds in Europe and Asia, is mainly grey above and white below except for the upper breast, which is grey like the upperparts, and the rump, which is white; the wings are grey with black wingtips. The female is brown above with white upper tail coverts, hence females, and the similar juveniles, are often called "ringtails". Their underparts are buff streaked with brown.[2]

The race C. c. hudsonius (Linnaeus, 1766) breeds in North America and is sometimes considered a distinct species, C. hudsonius.[5] The male's plumage is darker grey than that of C. c. cyaneus and the female is also darker and more rufous.[2] In both North American and Eurasia, the adult male is sometimes nicknamed the "Grey Ghost", because of his striking plumage and spectral aura.

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.[4]

Behaviour

This medium-sized raptor breeds on moorland, bogs, prairies, farmland coastal prairies, marshes, grasslands, swamps and other assorted open areas.[6] A male will maintain a territory averaging 2.6 km2 (1.0 sq mi), though male territories have ranged from 1.7 to 150 km2 (0.66 to 57.92 sq mi).[7]

These are the only hawk-like birds known to practice polygyny – one male mates with several females. Up to five females have been known to mate with one male in a season.[8] The nest is built on the ground or on a mound of dirt or vegetation. Nests are made of sticks and are lined inside with grass and leaves. Four to eight (exceptionally 2 to 10) whitish eggs are laid.[2][6] The eggs measure approximately 47 mm × 36 mm (1.9 in × 1.4 in).[9] The eggs are incubated mostly by the female for 31 to 32 days. When incubating eggs, the female sits on the nest while the male hunts and brings food to her and the chicks.[6] The male will help feed chicks after they hatch, but does not usually watch them for a greater period of time than around 5 minutes.[10] 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.[7] The chicks fledge at around 36 days old, though breeding maturity is not reached until 2 years in females and 3 years in males.

In winter, the hen harrier is a bird of open country, and will then roost communally, often with merlins and marsh harriers. There is now an accepted record of transatlantic vagrancy by the American subspecies, with a juvenile being recorded in Scilly, Great Britain from October 1982 to June 1983.[11]

Hunting behavior

This is a typical harrier, which hunts on long wings held in a shallow V in its low flight during which the bird closely hugs the contours of the land below it. Northern or hen 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 comprises small mammals.[12] 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).[5] The species has been observed to hunt bats if these are available.[13] Larger prey, such as rabbits and adult ducks are taken sometimes and harriers have been known to subdue these by drowning them in water.[5] Harriers hunt by surprising prey while flying low to the ground in open areas, as they drift low over fields and moors.[2][6] The harriers circle an area several times listening and looking for prey.[6] Harriers use hearing regularly to find prey, as they have exceptionally good hearing for diurnal raptors, this being the function of their owl-like facial disc.[5] This harrier tends to be a very vocal bird while it glides over its hunting ground.

Mortality and competition

Little information is available on longevity in hen or northern harriers. The longest lived known bird is 16 years and 5 months. However, adults rarely live more than 8 years. Early mortality mainly results from predation. Predators of eggs and nestlings include raccoons, skunks, badgers, foxes, crows and ravens, dogs and owls. Fledglings are also predated regularly, especially by great horned owls in North America.[14] Both parents attack potential predators with alarm calls and striking with talons. Short-eared owls are natural competitors 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.[15]

Status

This species has a large range, with an estimated global extent 1,000,000–20,000,000 km2 (390,000–7,720,000 sq mi), and a population estimated at 1.3 million individuals. There is evidence of a population decline, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations). It is therefore classified as "least concern".[1] In the United Kingdom, however, hen harrier populations are in a critical condition, due to habitat loss and illegal killing on grouse moors.[16] In 2012 only 617 pairs remained, representing a fall of 20% from 2004.

Relationship with humans

In some parts of Europe people believed that seeing a harrier perched on a house was a sign that three people would die; on a happier note, some Native American tribes believe that seeing a hawk on your wedding day is a sign of a long, happy marriage. Unlike many raptors, hen or northern harriers have historically been favorably regarded by farmers because they eat predators of quail eggs and mice that damage crops. Harriers are sometimes called "good hawks" because they pose no threat to poultry as some hawks do. Heavy pesticide use in the 1970s and 1980s caused a decline in harrier populations.[6]

Forestry and hen harriers

Eggs, Collection Museum Wiesbaden

The hen harrier is a bird of open habitats such as heather moorland and extensive agriculture. However, much of its range, particularly in Ireland and parts of western Britain, has been (and continues to be) afforested, predominantly with non-native conifers such as Sitka Spruce (Picea sitchensis) from North America.[17][18] Hen harriers nest and forage in commercial forestry when it is young, before the canopy closes (typically at between 9–12 and years old), but do not make much use of thicket and subsequent growth stages,[19][20] which typically comprise between 2⁄3 and 3⁄4 of the commercial growth cycle. Where forests replace habitats that were used by hen harriers they will therefore tend to reduce overall habitat availability.[21] However, where afforestation takes place in areas that were previously underutilised by hen harriers, it may increase the value of such areas to this species in the long-term.[22][23] Areas dominated by forestry may remain suitable to hen harriers provided that a mosaic of age classes is maintained within the forest, such that areas of young, pre-thicket forest are always available.

References

  1. 1 2 BirdLife International (2013). "Circus cyaneus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
  2. 1 2 3 4 5 6 7 del Hoyo, J.; Elliott, A.; Sargatal, J., eds. (1994). Handbook of the Birds of the World. Volume 2: New World Vultures to Guineafowl. Barcelona: Lynx Edicions. ISBN 84-87334-15-6.
  3. ↑ "Hen harrier". RSPB. Retrieved 2016-01-19.
  4. 1 2 Mullarney, Killian; Svensson, Lars; Zetterstrom, Dan; Grant, Peter (1999). Collins Bird Guide. London: HarperCollins. p. 86. ISBN 0-00-219728-6.
  5. 1 2 3 4 5 6 7 8 Ferguson-Lees, J.; Christie, D.A. (2001). Raptors of the World. London: Christopher Helm. ISBN 0-7136-8026-1.
  6. 1 2 3 4 5 6 "Northern Harrier (Circus cyaneus)". Wildlife Fact Sheets. Texas Parks and Wildlife Department. Retrieved 25 June 2012.
  7. 1 2 Macwhirter, R.; Bildstein, K. (1996). Northern Harrier. The Birds of North America. pp. 1–25.
  8. ↑ "Northern Harrier". All About Birds. Cornell Lab of Ornithology. Retrieved 23 August 2012.
  9. ↑ Baicich, P.; Harrison, C. (1997). A Guide to the Nests, Eggs, and Nestlings of North American Birds. New York, NY: Academic Press. ISBN 0120728311.
  10. ↑ Weidensaul, Scott (1996). Raptors: the birds of prey. Lyons & Burford. ISBN 978-1-55821-275-6.
  11. ↑ Fraser, P.A.; et al. (2007). "Report on rare birds in Great Britain in 2006" (PDF). British Birds 100 (12): 707.
  12. ↑ Ryser, F. (1985). Birds of the Great Basin: A Natural History. Reno, Las Vegas: University of Nevada Press. ISBN 087417080X.
  13. ↑ Mikula, P.; Morelli, F.; Lučan, R. K.; Jones, D. N.; Tryjanowski, P. (2016). "Bats as prey of diurnal birds: a global perspective". Mammal Review. doi:10.1111/mam.12060.
  14. ↑ Wheeler, B.; Clark, W. (1995). A Photographic Guide to North American Raptors. San Diego: Academic Press Inc. ISBN 071366763X.
  15. ↑ "Short-eared Owl – Asio flammeus". owlpages.com. 24 July 2013. Retrieved 1 December 2015.
  16. ↑ "Welcome to the hen harrier LIFE project". RSPB. Retrieved 2016-02-12.
  17. ↑ Barton, C.; Pollock, C.; Norriss, D.W.; Nagle, T.; Oliver, G.A.; Newton, S. (2006). "The second national survey of breeding hen harriers Circus cyaneus in Ireland". Irish Birds 8: 1–20.
  18. ↑ Fielding, A.; Haworth, P.; Whitfield, P.; McLeod, D. (2010). "Raptor species conservation frameworks: Hen Harrier framework project final report". Edinburgh: Scottish Natural Heritage.
  19. ↑ Madders, M. (2000). "Habitat selection and foraging success of hen harriers (Circus cyaneus) in west Scotland". Bird Study 47: 32. doi:10.1080/00063650009461158.
  20. ↑ O'Donoghue, B. (2004). The Hen Harrier in Ireland (Master's thesis). University College Dublin.
  21. ↑ O’Flynn, W.J. (1983). "Population changes of the hen harrier in Ireland". Irish Birds 2: 337–343.
  22. ↑ Wilson, M.W.; Irwin, S.; Norriss, D.W.; Newton, S.F.; Collins, K.; Kelly, T.C.; O'Halloran, J. (2009). "The importance of pre-thicket conifer plantations for nesting Hen Harriers (Circus cyaneus) in Ireland". Ibis 151 (2): 332. doi:10.1111/j.1474-919X.2009.00918.x.
  23. ↑ Haworth, P.F.; Fielding, A.H. (2009). An assessment of woodland habitat utilisation by breeding hen harriers. SNH Project No. 24069 (Edinburgh: Scottish Natural Heritage).

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