Animals / Birds

Common raven

Синонимы

Ворон (ру.)

Northern raven (en.)

Kolkrabe (de.)

Cuervo grande, cuervo común, corneja (es.)

Классификация

Order — Passeriformes.

Family — Corvidae.

Genus — Corvus.

Species — Corvus corax.

Ареал

Common ravens can thrive in varied climates; indeed this species 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, northern England and the west of Ireland. 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—described as Corvus corax laurencei(also spelt lawrencii or laurencii) by Allan Octavian Hume but more often considered synonymous with subcorax — is restricted to the Sindh district of Pakistan and adjoining regions of northwestern India. Except in Arctic habitats, they are generally resident within their range for the whole year. Young birds may disperse locally.

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.

Внешний вид

Length: 64 cm.

Wingspan: 120-150 cm.

Weight: 0.8-1.5 kg.

Necks are thick.

Ravens have beard of shaggy throat feathers, which is particularly evident when calling.

Bill is stout and very powefur looking.

On closer inspection the black feathers have a purplish sheen.

Bill and legs are black.

Juveniles are like the adults but browner and have paler eyes.

In flight, the tail is diamond-shaped, and the wing beat is very slow and purposeful.

Despite their size they are remarkably agile and perform allsorts of aerobatic tumbles, dives and even flip upside down, especially in the springtime.

Характер

The brains of common ravens count among the largest of any bird species. Specifically, their hyperpallium is large, for a bird. They display ability in problem-solving, as well as other cognitive processes such as imitation and insight.

Кормление

Common ravens are omnivorous and highly opportunistic: their diet may vary widely with location, season and serendipity. For example, those foraging on tundra on the Arctic North Slope of Alaska obtained about half their energy needs from predation, mainly of microtine rodents, and half by scavenging, mainly of caribou and ptarmigan carcasses.

In some places they are mainly scavengers, feeding on carrion as well as the associated maggots and carrion beetles. With large-bodied carrion, which they are not equipped to tear through as well as birds such as hook-billed vultures, they must wait for the prey to be torn open by another predator or flayed by other means. Plant food includes cereal grains, berries and fruit. They prey on small invertebrates, amphibians, reptiles, small mammals and birds. Ravens may also consume the undigested portions of animal feces, and human food waste. They store surplus food items, especially those containing fat, and will learn to hide such food out of the sight of other common ravens. Ravens also raid the food caches of other species, such as the Arctic fox. They sometimes associate with another canine, the grey wolf, as a kleptoparasite, following to scavenge wolf-kills in winter. Ravens are regular predators at bird nests, brazenly picking off eggs, nestlings and sometimes adult birds when they spot an opportunity. They are considered perhaps the primary natural threat to the nesting success of the critically endangered California condor, since they readily take condor eggs and are very common in the areas where the species is being re-introduced.

Common ravens nesting near sources of human garbage included a higher percentage of food waste in their diet, birds nesting near roads consumed more road-killed vertebrates, and those nesting far from these sources of food ate more arthropods and plant material. Fledging success was higher for those using human garbage as a food source. In contrast, a 1984–1986 study of common raven diet in an agricultural region of south-western Idaho found that cereal grains were the principal constituent of pellets, though small mammals, grasshoppers, cattle carrion and birds were also eaten.

One behavior is recruitment, where juvenile ravens call other ravens to a food bonanza, usually a carcass, with a series of loud yells. In Ravens in Winter, Bernd Heinrich posited that this behavior evolved to allow the juveniles to outnumber the resident adults, thus allowing them to feed on the carcass without being chased away. A more mundane explanation is that individuals co-operate in sharing information about carcasses of large mammals because they are too big for just a few birds to exploit. Experiments with baits however show that such recruitment behaviour is independent of the size of the bait.

Furthermore, there has been research suggesting that the common raven is involved in seed dispersal. In the wild, the common raven chooses the best habitat and disperses seeds in locations best suited for its survival.

Особенности
Болезни

Salmonella, Trichomoniasis, Aspergillosis, Avian pox, Mites and Lice, Lyme Disease.

Разведение

Juveniles begin to court at a very early age, but may not bond for another two or three years. Aerial acrobatics, demonstrations of intelligence, and ability to provide food are key behaviors of courting. Once paired, they tend to nest together for life, usually in the same location. Instances of non-monogamy have been observed in common ravens, by males visiting a female's nest when her mate is away.

Breeding pairs must have a territory of their own before they begin nest-building and reproduction, and thus aggressively defend a territory and its food resources. Nesting territories vary in size according to the density of food resources in the area. The nest is a deep bowl made of large sticks and twigs, bound with an inner layer of roots, mud, and bark and lined with a softer material, such as deer fur. The nest is usually placed in a large tree or on a cliff ledge, or less frequently in old buildings or utility poles.

Females lay between three and seven pale bluish-green, brown-blotched eggs. Incubation is about 18 to 21 days, by the female only. However, the male may stand or crouch over the young, sheltering but not actually brooding them. Young fledge at 35 to 42 days, and are fed by both parents. They stay with their parents for another six months after fledging.

In most of their range, egg laying begins in late February. In colder climates, it is later, e.g. April in Greenland and Tibet. In Pakistan, egg-laying takes place in December. Eggs and hatchlings are preyed on, rarely, by largehawks and eagles, large owls, martens and canids. The adults, which are very rarely predated, are often successful in defending their young from these predators, due to their numbers, large size and cunning. They have been observed dropping stones on potential predators that venture close to their nests.

Common ravens can be very long-lived, especially in captive or protected conditions; individuals at the Tower of London have lived for more than 40 years. Lifespans in the wild are considerably shorter at typically 10 to 15 years. The longest known lifespan of a banded wild common raven was 23 years, 3 months.

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