Alpine chough

Appearance

The adult of the nominate subspecies of the Alpine chough has glossy black plumage, a short yellow bill, dark brown irises, and red legs. It is slightly smaller than red-billed chough, at 37–39 centimetres length with a 12–14 cm tail and a 75–85 cm wingspan, but has a proportionally longer tail and shorter wings than its relative.

It has a similar buoyant and easy flight. The sexes are identical in appearance although the male averages slightly larger than the female. The juvenile is duller than the adult with a dull yellow bill and brownish legs. The Alpine chough is unlikely to be confused with any other species; although the jackdaw and red-billed chough share its range, the jackdaw is smaller and has unglossed grey plumage, and the red-billed chough has a long red bill.

The subspecies "P. g. digitatus" averages slightly larger than the nominate form, weighing 191–244 grams against 188–252 g for "P. g. graculus", and it has stronger feet. This is in accordance with Bergmann's rule, which predicts that the largest birds should be found higher elevations or in colder and more arid regions. The extremities of the body, the bill and tarsus, were longer in warmer areas, in line with Allen's rule. Temperature seemed to be the most important cause of body variation in the Alpine chough.

Distribution

The Alpine Chough breeds in mountains from Spain eastwards through southern Europe and the Alps across Central Asia and the Himalayas to western China. There are also populations in Morocco, Corsica and Crete. It is a non-migratory resident throughout its range, although Moroccan birds have established a small colony near Málaga in southern Spain, and wanderers have reached Czechoslovakia, Gibraltar, Hungary and Cyprus.

Behavior

The flight of the Alpine chough is swift and acrobatic with loose deep wing beats. Its high manoeuvrability is accomplished by fanning the tail, folding its wings, and soaring in the updraughts at cliff faces. Even in flight, it can be distinguished from the red-billed chough by its less rectangular wings, and longer, less square-ended tail.

The rippling "preep" and whistled "sweeeooo" calls of the Alpine chough are quite different from the more typically crow-like "chee-ow" vocalisations of the jackdaw and the red-billed chough. It also has a rolling "churr" alarm call, and a variety of quiet warbles and squeaks given by resting or feeding birds. In a study of chough calls throughout the Palearctic region it was found that call frequencies in the Alpine chough showed an inverse relationship between body size and frequency, being higher-pitched in smaller-bodied populations.

Habitat

This is a high-altitude species normally breeding between 1,260–2,880 metres in Europe, 2,880–3,900 m in Morocco, and 3,500–5,000 m in the Himalayas. It has nested at 6,500 m, higher than any other bird species, even surpassing the Red-billed chough which has a diet less well adapted to the highest altitudes.

It has been observed following mountaineers ascending Mount Everest at an altitude of 8,200 m. It usually nests in cavities and fissures on inaccessible rock faces, although locally it will use holes between rocks in fields, and forages in open habitats such as alpine meadows and scree slopes to the tree line or lower, and in winter will often congregate around human settlements, ski resorts, hotels and other tourist facilities. Its penchant for waiting by hotel windows for food is popular with tourists, but less so with hotel owners.

Reproduction

The Alpine chough is socially monogamous, showing high partner fidelity in summer and winter and from year to year. Nesting typically starts in early May, and is non-colonial, although in suitable habitat several pairs may nest in close proximity.

The bulky nests are composed of roots, sticks and plant stems lined with grass, fine twiglets or hair, and may be constructed on ledges, in a cave or similar fissure in a cliff face, or in an abandoned building. The clutch is 3–5 glossy whitish eggs, averaging 33.9 by 24.9 millimetres in size, which are tinged with buff, cream or light-green and marked with small brown blotches; they are incubated by the female for 14–21 days before hatching. The chicks hatch with a dense covering of natal down, in contrast to those of the red-billed chough which are almost naked, and fledge in a further 29–31 days from hatching.

The young birds are fed by both parents, and may also be fed by other adults when they have fledged and joined the flock. Breeding is possible in the high mountains because chough eggs have relatively fewer pores than those of lowland species, and lose less water by evaporation at low atmospheric pressure. The embryos of bird species that breed at high altitude also have haemoglobin with a genetically determined high affinity for oxygen.

In the western Italian Alps, the Alpine chough nests in a greater variety of sites than red-billed chough, using natural cliffs, pot-holes and abandoned buildings, whereas the red-billed uses only natural cliffs. The Alpine chough lays its eggs about one month later than its relative, although breeding success and reproductive behaviour are similar. The similarities between the two species presumably arose because of the same strong environmental constraints on breeding behaviour.

A study of three different European populations showed a mean clutch size of 3.6 eggs, producing 2.6 chicks, of which 1.9 fledged. Adult survival rate varied from 83 to 92%, with no significant difference detected between males and females. Survival of first-year birds was, at 77%, lower than that of adults. The availability or otherwise of human food supplied from tourist activities did not affect breeding success.

Food

In the summer, the Alpine chough feeds mainly on invertebrates collected from pasture, such as beetles, snails, grasshoppers, caterpillars and fly larvae. The diet in autumn, winter and early spring becomes mainly fruit, including berries such as the European Hackberry and Sea-buckthorn, rose hips, and domesticated crops such as apples, grapes and pears where available. It has been observed eating flowers of "Crocus vernus albiflorus", including the pistils, perhaps as a source of carotenoids. The chough will readily supplement its winter diet with food provided by tourist activities in mountain regions, including ski resorts, refuse dumps and picnic areas. Where additional food is available, winter flocks are larger and contain a high proportion of immature birds. The young birds principally frequent the sites with the greatest food availability, such as refuse dumps. Both chough species will hide food in cracks and fissures, concealing the cache with a few pebbles.

This bird always forages in groups, which are larger in winter than summer, and have constant composition in each season. Where food resources are restricted, adults dominate young birds, and males outrank females. Foraging areas change altitudinally through the year, depending on climatic factors, food availability and food quality. During the breeding season, birds remain above the tree line, although they may use food provided by tourists at refuges and picnic areas.

Movement to lower levels begins after the first snowfalls, and feeding by day is mainly in or near valley bottoms when the snow cover deepens, although the birds return to the mountains to roost. In March and April the choughs frequent villages at valley tops or forage in snow-free patches prior to their return to the high meadows. Feeding trips may cover 20 km distance and 1,600 m in altitude. In the Alps, the development of skiing above 3,000 m has enabled more birds to remain at high levels in winter.

Where their ranges overlap, the two chough species may feed together in the summer, although 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 dug from the ground, whilst the Alpine chough took berries and hips. In June, red-billed choughs fed mainly on caterpillars whereas Alpine choughs ate crane fly pupae. Later in the summer, the Alpine chough consumed large numbers of grasshoppers, while the red-billed chough added cranefly pupae, fly larvae and beetles to its diet. In the eastern Himalayas in November, Alpine choughs occur mainly in juniper forests where they feed on juniper berries, differing ecologically from the red-billed choughs in the same region and at the same time of year, which feed by digging in the soil of terraced pastures of villages.

Predators

Predators of the choughs include the peregrine falcon, golden eagle and Eurasian eagle-owl, while the common raven will take nestlings.

Alpine choughs have been observed diving at a Tibetan red fox. It seems likely that this "mobbing" behaviour may be play activity to give practice for when genuine defensive measures may be needed to protect eggs or young.

The Alpine chough is a host of the widespread bird flea "Ceratophyllus vagabunda", two specialist chough fleas "Frontopsylla frontalis" and "F. laetus", a cestode "Choanotaenia pirinica", and various species of chewing lice in the genera "Brueelia", "Menacanthus" and "Philopterus".