Red-billed chough

Appearance

The adult of the "nominate" subspecies of the red-billed chough, "P. p. pyrrhocorax", is 39–40 centimetres in length, has a 73–90 centimetres 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

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.

Habitat

Its main habitat is high mountains; it is found between 2,000 and 2,500 metres in North Africa, and mainly between 2,400 and 3,000 metres in the Himalayas. In that mountain range it reaches 6,000 metres in the summer, and has been recorded at 7,950 metres 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.

Reproduction

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 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.

Food

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 reflects the thin soils which it feeds on, and the depths at which many invertebrates occur, but it may dig to 10–20 cm 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.

Predators

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.

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.