Red-billed chough

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 (pyrrhos), "flame-coloured", and κόραξ (korax), "raven". The only other member of the genus is the Alpine chough, Pyrrhocorax graculus. The closest relatives of the choughs are the typical crows, Corvus, especially the jackdaws in the subgenus Coloeus.

"Chough" was originally an alternative onomatopoeic name for the jackdaw, Corvus 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 only distantly related to the true choughs, and is an example of convergent evolution.

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 far west of Wales and Scotland, although it recolonised Cornwall in 2001 after an absence of 50 years.
• P. p. erythropthalmus, described by Louis Jean 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. erythropthalmus, 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.

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.

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.

Description

The adult of the "nominate" subspecies of the red-billed chough, P. p. pyrrhocorax, is 39–40 centimetres (15–16 inches) in length, has a 73–90 centimetres (29–35 inches) wingspan, and weighs an average 310 grammes (10.9 oz). 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 (although adults can be sexed in the hand using a formula involving tarsus length and bill width) 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, southern Europe and the Mediterranean basin, the Alps, 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 2,000 and 2,500 metres (6,600 and 8,200 ft) in North Africa, and mainly between 2,400 and 3,000 metres (7,900 and 9,800 ft) in the Himalayas. In that mountain range it reaches 6,000 metres (20,000 feet) in the summer, and has been recorded at 7,950 metres (26,080 feet) 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.

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; in central Asia, the hair may be taken from live Himalayan tahr. 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 3.9 by 2.8 centimetres (1.5 by 1.1 inches) in size and weighing 15.7 grammes (0.55 oz), 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. The Central Asian subspecies P. p. centralis will perch on the backs of wild or domesticated mammals to feed on parasites. 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 2–3 cm (1–1 in) reflects the thin soils which it feeds on, and the depths at which many invertebrates occur, but it may dig to 10–20 cm (4–8 in) 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.

Natural threats

The red-billed chough's predators include the peregrine falcon, golden eagle and Eurasian eagle-owl, while the common raven will take nestlings. In northern Spain, red-billed choughs preferentially nest near lesser kestrel colonies. This small insectivorous falcon is better at detecting a predator and more vigorous in defence than its corvid neighbours. The breeding success of the red-billed chough in the vicinity of the kestrels was found to be much higher than that of birds elsewhere, with a lower percentage of nest failures (16% near the falcon, 65% elsewhere).

This species is occasionally parasitised by the great spotted cuckoo, a brood parasite for which the Eurasian magpie is the primary host. Red-billed choughs can acquire blood parasites such as Plasmodium, but a study in Spain showed that the prevalence was less than one percent, and unlikely to affect the life history and conservation of this species. These low levels of parasitism contrast with a much higher prevalence in some other passerine groups; for example a study of thrushes in Russia showed that all the fieldfares, redwings and song thrushes sampled carried haematozoans, particularly Haemoproteus and Trypanosoma.

Red-billed choughs can also carry mites, but a study of the feather mite Gabucinia delibata, acquired by young birds a few months after fledging when they join communal roosts, suggested that this parasite actually improved the body condition of its host. It is possible that the feather mites enhance feather cleaning and deter pathogens, and may complement other feather care measures such as sunbathing, and anting—rubbing the plumage with ants (the formic acid from the insects deters parasites).

Status

The red-billed chough has an extensive range, estimated at 10 million square kilometres (3.8 million sq mi), and a large population, including an estimated 86,000 to 210,000 individuals in Europe. Over its range as a whole, the species is not believed to approach the thresholds for the global population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations), and is therefore evaluated as least concern.

However, the European range has declined and fragmented due to the loss of traditional pastoral farming, persecution and perhaps disturbance at breeding and nesting sites, although the numbers in France, Great Britain and Ireland may now have stabilised. The European breeding population is between 12,265–17,370 pairs, but only in Spain is the species still widespread. Since in the rest of the continent breeding areas are fragmented and isolated, the red-billed chough has been categorised as "vulnerable" in Europe.

In Spain, the red-billed chough has recently expanded its range by utilising old buildings, with 1,175 breeding pairs in a 9,716 square kilometres (3,751 square miles)mi) study area. These new breeding areas usually surround the original montane core areas. However, the populations with nest sites on buildings are threatened by human disturbance, persecution and the loss of old buildings. Fossils of both chough species were found in the mountains of the Canary Islands. The local extinction of the Alpine chough and the reduced range of red-billed chough in the islands may have been due to climate change or human activity.

A small group of wild red-billed chough arrived naturally in Cornwall in 2001, and nested in the following year. This was the first English breeding record since 1947, and a slowly expanding population has bred every subsequent year.

In Jersey, the Durrell Wildlife Conservation Trust, in partnership with the States of Jersey and the National Trust for Jersey began a project in 2010, aimed at restoring selected areas of Jersey's coastline with the intention of returning those birds that had become locally extinct. The red-billed chough was chosen as a flagship species for this project, having been absent from Jersey since around 1900. Durrell initially received two pairs of choughs from Paradise Park in Cornwall and began a captive breeding programme. In 2013, juveniles were released onto the north coast of Jersey using soft-release methods developed at Durrell. Over the next five years, small cohorts of captive-bred choughs were released, monitored, and provided supplemental food.