Red-billed chough
The red-billed chough, Cornish chough or simply chough is a bird in the crow family, one of only two species in the genus Pyrrhocorax. Its eight subspecies breed on mountains and coastal cliffs from the western coasts of Ireland and Britain east through southern Europe, North Africa and Middle East to Central Asia, India and China.
This bird has glossy black plumage, a long curved red bill, red legs, and a loud, ringing call. It has a buoyant acrobatic flight with widely spread primaries. The red-billed chough pairs for life and displays fidelity to its breeding site, which is usually a cave or crevice in a cliff face. It builds a wool-lined stick nest and lays three eggs. It feeds, often in flocks, on short grazed grassland, taking mainly invertebrate prey.
Although it is subject to predation and parasitism, the main threat to this species is changes in agricultural practices, which have led to population decline, some local extinction and range fragmentation in Europe; however, it is not threatened globally. The red-billed chough, which derived its common name 'chough' from the jackdaw, was formerly associated with fire-raising, and has links with Saint Thomas Becket and Cornwall.
Taxonomy
The red-billed chough was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae as Upupa pyrrhocorax. It was moved to its current genus, Pyrrhocorax, by Marmaduke Tunstall in his 1771 Ornithologia Britannica. The genus name is derived from Greek πυρρός , "flame-coloured", and κόραξ , "raven". The only other member of the genus is the Alpine chough Pyrrhocorax graculus; hybrids with Alpine chough are known.Traditionally, the closest relatives of the choughs have been thought to be the typical crows Corvus and the jackdaws Coloeus, but more recent genetic studies have suggested the choughs are basal to a group of Asian jay genera, or most recently, basal in the entire Corvidae.
Subspecies
There are eight extant subspecies, although differences between them are slight.- P. p. pyrrhocorax, the nominate subspecies and smallest form, is endemic to the British Isles, where it is restricted to Ireland, the Isle of Man, and the west of Wales, southwest Scotland, and Cornwall, which it recolonised in 2001 after an absence of 50 years.
- P. p. erythroramphos, described by Louis Pierre Vieillot in 1817 as Coracia erythrorhamphos, occurs in the red-billed chough's continental European range, excluding Greece. It is larger and slightly greener than the nominate race.
- P. p. barbarus, described by Charles Vaurie under its current name in 1954, is resident in North Africa and on La Palma in the Canary Islands. Compared to P. p. erythroramphos, it is larger, has a longer tail and wings, and its plumage has a greener gloss. It is the longest-billed form, both absolutely and relatively.
- P. p. baileyi described by Austin Loomer Rand and Charles Vaurie under its current name in 1955, is a dull-plumaged subspecies endemic to Ethiopia, where it occurs in two separate areas. The two populations could possibly represent different subspecies.
- P. p. docilis, described by Johann Friedrich Gmelin as Corvus docilis in 1774, breeds from Greece to Afghanistan. It is larger than the African subspecies, but it has a smaller bill and its plumage is very green-tinted, with little gloss.
- P. p. himalayanus, described by John Gould in 1862 as Fregilus himalayanus, is found from the Himalayas to western China, but intergrades with P. p. docilis in the west of its range. It is the largest subspecies, long-tailed, and with blue or purple-blue glossed feathers.
- P. p. centralis, described by Erwin Stresemann in 1928 under its current name, breeds in Central Asia. It is smaller and less strongly blue than P. p. himalayanus, but its distinctness from the next subspecies has been questioned.
- P. p. brachypus, described by Robert Swinhoe in 1871 as Fregilus graculus var. brachypus, breeds in central and northern China, Mongolia and southern Siberia. It is similar to P. p. centralis but with a weaker bill.
Detailed analysis of call similarity suggests that the Asiatic and Ethiopian races diverged from the western subspecies early in evolutionary history, and that Italian red-billed choughs are more closely allied to the North African subspecies than to those of the rest of Europe.
There is one known prehistoric form of the red-billed chough. P. p. primigenius, a subspecies that lived in Europe during the last ice age, which was described in 1875 by Alphonse Milne-Edwards from finds in southwest France.
Etymology
"Chough" was originally an alternative onomatopoeic name for the jackdaw Coloeus monedula, based on its call. The similar red-billed species, formerly particularly common in Cornwall, became known initially as "Cornish chough" and then just "chough", the name transferring from one species to the other.The Australian white-winged chough Corcorax melanorhamphos, despite its similar shape and habits, is in a separate family Corcoracidae only moderately related to the Corvidae and not notably to the true choughs, and is an example of convergent evolution.
Description
The adult of the "nominate" subspecies of the red-billed chough, P. p. pyrrhocorax, is in length, has a wingspan, and weighs an average 310 grammes. Its plumage is velvet-black, green-glossed on the body, and it has a long curved red bill and red legs. The sexes are similar but the juvenile has an orange bill and pink legs until its first autumn, and less glossy plumage.The red-billed chough is unlikely to be confused with any other species of bird. Although the jackdaw and Alpine chough share its range, the jackdaw is smaller and has unglossed grey plumage, and the Alpine chough has a short yellow bill. Even in flight, the two choughs can be distinguished by Alpine's less rectangular wings, and longer, less square-ended tail.
The red-billed chough's loud, ringing chee-ow call is clearer and louder than the similar vocalisation of the jackdaw, and always very different from that of its yellow-billed congener, which has rippling preep and whistled sweeeooo calls. Small subspecies of the red-billed chough have higher frequency calls than larger races, as predicted by the inverse relationship between body size and frequency.
Distribution and habitat
The red-billed chough breeds in Ireland, western Great Britain, the Isle of Man, Brittany, the Alps, La Palma in the Canary Islands, across southern Europe and the Mediterranean basin, northern Arabia, northern Iraq, Iran, Afghanistan, and in mountainous country across Central Asia, India and China, with two separate populations in the Ethiopian Highlands. It is a non-migratory resident throughout its range.Its main habitat is high mountains; it is found between in North Africa, and mainly between in the Himalayas. In that mountain range it reaches in the summer, and has been recorded at altitude on Mount Everest. In the British Isles and Brittany it also breeds on coastal sea cliffs, feeding on adjacent short grazed grassland or machair. It was formerly more widespread on coasts but has suffered from the loss of its specialised habitat. It tends to breed at a lower elevation than the Alpine chough, that species having a diet better adapted to high altitudes.
Behaviour and ecology
Breeding
The red-billed chough breeds from three years of age, and normally raises only one brood a year, although the age at first breeding is greater in large populations. A pair exhibits strong mate and site fidelity once a bond is established. The bulky nest is composed of roots and stems of heather, furze or other plants, and is lined with wool or hair. The nest is constructed in a cave or similar fissure in a crag or cliff face. In soft sandstone, the birds themselves excavate holes nearly a metre deep. Old buildings may be used, and in Tibet working monasteries provide sites, as occasionally do modern buildings in Mongolian towns, including Ulaanbaatar. The red-billed chough will utilise other artificial sites, such as quarries and mineshafts for nesting where they are available.The chough lays three to five eggs in size and weighing 15.7 grammes, of which 6% is shell. They are spotted, not always densely, in various shades of brown and grey on a creamy or slightly tinted ground.
The egg size is independent of the clutch size and the nest site, but may vary between different females. The female incubates for 17–18 days before the altricial downy chicks are hatched, and is fed at the nest by the male. The female broods the newly hatched chicks for around ten days, and then both parents share feeding and nest sanitation duties. The chicks fledge 31–41 days after hatching.
Juveniles have a 43% chance of surviving their first year, and the annual survival rate of adults is about 80%. Choughs generally have a lifespan of about seven years, although an age of 17 years has been recorded. The temperature and rainfall in the months preceding breeding correlates with the number of young fledging each year and their survival rate. Chicks fledging under good conditions are more likely to survive to breeding age, and have longer breeding lives than those fledging under poor conditions.
Feeding
The red-billed chough's food consists largely of insects, spiders and other invertebrates taken from the ground, with ants probably being the most significant item. Although invertebrates make up most of the chough's diet, it will eat vegetable matter including fallen grain, and in the Himalayas has been reported as damaging barley crops by breaking off the ripening heads to extract the corn. In the Himalayas, they form large flocks in winter.The preferred feeding habitat is short grass produced by grazing, for example by sheep and rabbits, the numbers of which are linked to the chough's breeding success. Suitable feeding areas can also arise where plant growth is hindered by exposure to coastal salt spray or poor soils. It will use its long curved bill to pick ants, dung beetles and emerging flies off the surface, or to dig for grubs and other invertebrates. The typical excavation depth of reflects the thin soils which it feeds on, and the depths at which many invertebrates occur, but it may dig to in appropriate conditions.
Where the two chough species occur together, there is only limited competition for food. An Italian study showed that the vegetable part of the winter diet for the red-billed chough was almost exclusively Gagea bulbs, whilst the Alpine chough took berries and hips. In June, red-billed choughs fed on Lepidoptera larvae whereas Alpine choughs ate cranefly pupae. Later in the summer, the Alpine chough mainly consumed grasshoppers, whilst the red-billed chough added cranefly pupae, fly larvae and beetles to its diet. Both choughs will hide food in cracks and fissures, concealing the cache with a few pebbles.