Common Raven

Description

A mature common raven ranges between 54 and 71 cm (21 and 28 in) and has a wingspan of 116 to 153 cm (46 to 60 in). Recorded weights range from 0.69 to 2.250 kg (1.52 to 4.96 lb), thus making the common raven one of the heaviest passerines. Birds from colder regions such as the Himalayas and Greenland are generally larger with slightly larger bills, while those from warmer regions are smaller with proportionally smaller bills. Representative of the size variation in the species, ravens from California weighed an average of 0.784 kg (1.73 lb), those from Alaska weighed an average of 1.135 kg (2.50 lb) and those from Nova Scotia weighed an average of 1.230 kg (2.71 lb). The bill is large and slightly curved, with a culmen length of 5.7 to 8.5 cm (2.2 to 3.3 in), one of the largest bills amongst passerines (only the thick-billed raven and white-necked raven have larger bills). It has a longish, strongly graduated tail, at 20 to 26.3 cm (7.9 to 10.4 in), and mostly iridescent black plumage, and a dark brown iris. The throat feathers are elongated and pointed and the bases of the neck feathers are pale brownish-grey. The legs and feet are stout and strong, with a tarsus length of 6 to 7.2 cm (2.4 to 2.8 in). The juvenile plumage is similar but duller, with a blue-grey iris, and pinkish gape at first. Apart from its greater size, the common raven differs from related crows by having a larger and heavier black beak, shaggy feathers around the throat, longer bristles above the beak, and a longer, wedge-shaped tail. Flying ravens are distinguished from crows by their tail shape, larger wing area, and more stable soaring style, which generally involves less wing flapping. Despite their bulk, ravens are easily as agile in flight as their smaller cousins. In flight the feathers produce a creaking sound that has been likened to the rustle of silk. The voice of ravens is also quite distinct, its usual call being a deep croak of a much more sonorous quality than a crow's call, though the calls of other ravens like the fan-tailed raven and brown-necked raven can be confused where they occur together with common ravens in parts of southwest Asia and northern Africa; of these two, the fan-tailed raven is more similar in calls but has a very different shape with its broad wings and very short tail, while the brown-necked raven can be very hard to distinguish on plumage, but has somewhat more crow-like calls. In North America, the Chihuahuan raven (C. cryptoleucus) is fairly similar to the relatively small common ravens of the American southwest and is best distinguished by the still relatively smaller size of its bill, beard and body and relatively longer tail. The all-black carrion crow (C. corone) and rook (C. frugilegus) in Europe may suggest a raven due to their largish bill but are still distinctly smaller and have the wing and tail shapes typical of crows. In the Faroe Islands, a now-extinct pied colour morph of this species existed, known as the pied raven; the ordinary black-coloured common ravens remain widespread in the archipelago. White ravens are occasionally found in the wild. Some in British Columbia lacked the pink eyes of an albino, and were instead leucistic, a condition where an animal lacks any of several different types of pigment, not simply melanin. Common ravens have a wide range of vocalizations which are of interest to ornithologists. Gwinner carried out important studies in the early 1960s, recording and photographing his findings in great detail. Fifteen to 30 categories of calls have been recorded for this species, most of which are used for social interaction. Calls recorded include alarm calls, chase calls, and flight calls. The species has a distinctive, deep, resonant prruk-prruk-prruk call, which to experienced listeners is unlike that of any other corvid. Its very wide and complex vocabulary includes a high, knocking toc-toc-toc, a dry, grating kraa, a low guttural rattle and some calls of an almost musical nature. Like other corvids, the common raven can mimic sounds from their environment, including human speech. Non-vocal sounds produced by the common raven include wing whistles and bill snapping. Clapping or clicking has been observed more often in females than in males. If a member of a pair is lost, its mate reproduces the calls of its lost partner to encourage its return.

Range & habitat

The common raven can thrive in varied climates; it has the largest range of any member of the genus, and one of the largest of any passerine. They range throughout the Holarctic from Arctic and temperate habitats in North America and Eurasia to the deserts of North Africa, and to islands in the Pacific Ocean. In the British Isles, they are more common in Scotland, Wales, western England and Ireland, having been eradicated from other areas by gamekeeping interests. In Tibet, they have been recorded at altitudes up to 5,000 m (16,400 ft), and as high as 6,350 m (20,600 ft) on Mount Everest. The population sometimes known as the 'Punjab raven', part of the subspecies Corvus corax laurencei (sometimes misnamed C. c. subcorax) occurs in the Sindh district of Pakistan and adjoining regions of northwestern India. They are generally resident within their range for the whole year. In his 1950 work, Grønlands Fugle [Birds of Greenland], noted ornithologist Finn Salomonsen indicated that common ravens did not overwinter in the Arctic. However, in Arctic Canada and Alaska, they are found year-round. Young birds may disperse locally. In the United Kingdom, the range is currently increasing after improved legal protection, but illegal persecution by gamekeepers remains a problem in many areas. It favours mountainous or coastal terrain, but can also be found in parks with tall trees suitable for use as habitation. Its population is at its most dense in the north and west of the country, though the species is expanding its population southwards. Most common ravens prefer wooded areas with large expanses of open land nearby, or coastal regions for their nesting sites and feeding grounds. In some areas of dense human population, such as California in the United States, they take advantage of a plentiful food supply and have seen a surge in their numbers. On coasts, individuals of this species are often evenly distributed and prefer to build their nest sites along sea cliffs. Common ravens are often located in coastal regions because these areas provide easy access to water and a variety of food sources. Also, coastal regions have stable weather patterns without extreme cold or hot temperatures. In general, common ravens live in a wide array of environments but prefer heavily contoured landscapes. When the environment changes in vast degrees, these birds will respond with a stress response. The hormone known as corticosterone is activated by the hypothalamic–pituitary–adrenal axis. Corticosterone is activated when the bird is exposed to stress, such as migrating great distances.

Behaviour

Common ravens usually travel in mated pairs, although young birds may form flocks. Relationships between common ravens are often quarrelsome, yet they demonstrate considerable devotion to their families.

Adapted from Common raven on Wikipedia, used under CC BY-SA 4.0.