Thehen harrier (Circus cyaneus) is abird of prey. It breeds inEurasia. The term "hen harrier" refers to its former habit of preying on free-ranging fowl.[2]
Itmigrates to more southerly areas in winter. Eurasian birds move to southern Europe and southern temperate Asia. In the mildest regions, such as France andGreat Britain, hen harriers may be present all year, but the higher ground is largely deserted in winter.
In 1758 the English naturalistGeorge Edwards included an illustration and a description of the hen harrier in the first volume of hisGleanings of Natural History. He used the English name "The blue hawk". Edwards based his hand-coloured etching on a bird that had been shot near London.[3] When in 1766 the Swedish naturalistCarl Linnaeus updated hisSystema Naturae for thetwelfth edition, he placed the hen harrier with the falcons and eagles in thegenusFalco. Linnaeus included a brief description, coined thebinomial nameFalco cyaneus and cited Edwards' work.[4] The hen harrier is now placed in the genusCircus that was introduced by the French naturalistBernard Germain de Lacépède in 1799.[5][6] The genus nameCircus is derived from theAncient Greekkirkos, referring to a bird of prey named for its circling flight (kirkos, "circle"). The specific epithetcyaneus is fromLatin and means "dark blue".[7] The species ismonotypic: nosubspecies are recognised.[6]
The hen harrier is 41–52 cm (16–20 in)[10] long with a 97–122 cm (38–48 in) wingspan.[11][12] It resembles otherharriers 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).[10][12] Among standard measurements, thewing chord is 32.8 to 40.6 cm (12.9 to 16.0 in), thetail is 19.3 to 25.8 cm (7.6 to 10.2 in) and thetarsus is 7.1 to 8.9 cm (2.8 to 3.5 in).[12] It is relatively long winged and long tailed.[12]
The male 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 with brown barring.[10] Juveniles resemble females but with less distinct barring, dark brown secondaries dark brown and less-barred belly.[13]
The female gives a whistledpiih-eh when receiving food from the male, and her alarm call ischit-it-it-it-it-et-it. The male callschek-chek-chek, with a more bouncingchuk-uk-uk-uk during his display flight.[11]
These are one of the few raptorial birds known to practicepolygyny – one male mates with several females. Up to five females have been known to mate with one male in a season. A supplementary feeding experiment on the Orkney islands showed that rates of polygyny were influenced by food levels; males provided with extra food had more breeding females than 'control' males that received no extra food.[14]
The nest is constructed 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) whitisheggs are laid. The eggs measure approximately 47 mm × 36 mm (1.9 in × 1.4 in). 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. 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.[15] 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 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 withmerlins andmarsh harriers. There is now an accepted record oftransatlantic vagrancy by the northern harrier, with a juvenile being recorded inScilly,Great Britain from October 1982 to June 1983.[16]
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 smallmammals, as do most harriers. Up to 95% of the diet comprises small mammals. However,birds are hunted with some regularity as well, especially by males. Preferred avian prey includepasserines of open country (i.e.sparrows,larks,pipits), smallshorebirds and the young ofwaterfowl andgalliforms. Supplementing the diet occasionally areamphibians (especiallyfrogs),reptiles andinsects (especiallyorthopterans).[12] The species has been observed to huntbats if these are available.[17] Larger prey, such asrabbits and adultducks are taken sometimes and harriers have been known to subdue these by drowning them in water.[12] Harriers hunt by surprising prey while flying low to the ground in open areas, as they drift low over fields and moors.[10] The harriers circle an area several times listening and looking for prey. Harriers use hearing regularly to find prey, as they have exceptionally good hearing for diurnal raptors, this being the function of theirowl-like facial disc.[12] This harrier tends to be a very vocal bird while it glides over its hunting ground.
Little information is available on the longevity in hen harriers. The longest-lived known bird is 16 years and 5 months. However, adults rarely live beyond 8 years. Early mortality is mainly due to predation. Predators of eggs and nestlings includeraccoons,skunks,badgers,foxes,crows and ravens,dogs andowls. Both parents attack potential predators with alarm calls and striking with talons.Short-eared owls are natural competitors of this species, preferring the same prey and habitat, and having a similar geographic 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 askleptoparasitism. Most often, the harriers are the aggressors, stealing prey from the owls.[18]
This species has a wide geographical distribution and, although there is evidence of a population decline, it is not thought to be approaching the thresholds for theIUCN Red List criterion of population decline (i.e., a decline of more than 30% in ten years or three generations). It is therefore classified as "least concern".[1] However, in Britain and Ireland, hen harrier populations are in a critical state, mainly due to habitat loss and illegal shooting ongrouse moors.[19][20] There is sufficient suitable habitat to support over 300 breeding pairs of hen harriers in England alone, yet only 34 successful nests were recorded in 2022. Furthermore, many of the young birds do not survive beyond their first year, before the onset of sexual maturity at the age of two. Most UK Hen Harriers are found in Scotland, but even there the population declined by 27% between 2004 and 2016.
In some parts of Europe people believed that seeing a hen harrier perched on a house was a sign that three people would die. Unlike many raptors, hen harriers have historically been looked upon favorably by farmers because they eat predators of quail eggs and mice that damage crops. Harriers are sometimes called "good hawks" because they do not pose a threat to poultry as some hawks do.[citation needed]
The hen harrier is a bird of open habitats such as heather moorland and extensive agricultural land. However, much of its range, particularly in Ireland and parts of western Britain, has been (and continues to be) afforested, mainly with non-native conifers such asSitka spruce (Picea sitchensis) from North America.[21][22] Hen harriers nest and forage in commercial forestry plantations before the canopy closes (typically at between 9 and 12 years old), but do not make much use of thicket and later growth stages,[23][24] which typically comprise between2⁄3 and3⁄4 of the commercial growth cycle. Where afforestation replaces habitats previously used by hen harriers they will therefore tend to reduce overall habitat availability.[25] However, where afforestation takes place in areas that were previously underutilised by hen harriers, it may increase the value of such areas to the species in the long-term.[26][27] Areas dominated by forestry may remain suitable to hen harriers provided that a mosaic of age classes is maintained within the forest so that areas of young, pre-thicket forest are always available.
^Mikula, P.; Morelli, F.; Lučan, R. K.; Jones, D. N.; Tryjanowski, P. (2016). "Bats as prey of diurnal birds: a global perspective".Mammal Review.46 (3):160–174.doi:10.1111/mam.12060.
^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.
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