Raven

The greater raven's range is wide, and the species is not in danger of extinction. In some regions, there are localized declines caused by habitat loss and persecution. Elsewhere, populations have increased significantly and have become agricultural pests. The raven can cause damage to nut and grain crops and may also harm livestock. In particular, it can kill goats, lambs, and calves. Ravens generally attack the heads of newborn cattle, but their larger scavenging behavior can be mistaken for predation by ranchers. West of the Mojave Desert, human settlement and land cultivation led to a multiplication of raven populations over a period of 16 to 25 years. Cities, garbage dumps, artificial lakes, and wastewater treatment plants create food and water sources for the birds. Ravens also use utility poles as nesting sites and are sometimes struck by roadside collisions. The population explosion in the Mojaves Desert has heightened concerns for the endangered desert tortoise. The raven is a predator of young tortoises, which have soft shells and move slowly. Controlling the large raven population includes trapping and contacting landfill managers to reduce the amount of exposed waste.

Habitat edit Most crows prefer coastal areas or forested areas with large open spaces nearby for nesting and feeding. In some regions with high concentrations of human populations, such as California in the United States, they take advantage of abundant food sources, and their numbers are increasing.

Distribution edit

Two young people in Iceland. The raven is able to thrive in a wide range of climates; indeed, this species has the widest range of any member of its class.[15] Its range extends across the Holo-Arctic, from the Arctic and temperate habitats of North America and Europe to the deserts of North Africa and the Pacific Islands. In the British Isles, it is largest in Scotland, northern England, and western Ireland. In Tibet, it has been observed at altitudes of 5,000 m and up to 6,350 m on Everest.

Migration edit The raven is generally a permanent resident throughout its range except in the Arctic. Young individuals may disperse locally.[16]

The interior is lined with softer materials such as deer hair. The nest is usually located in a large tree, on a rocky outcrop, or, more frequently, on old buildings or electricity pylons. Females lay three to seven pale blue-green eggs spotted with brown. In most of their range, laying begins in late February. In colder climates, eggs are laid later; in Greenland and Tibet, they are laid in April. In Pakistan, laying takes place in December. Only the female incubates, and incubation lasts 18 to 21 days. However, the male may sit on top of the eggs, guarding them without brooding them. The parents will feed the young that leave the nest 35 to 42 days after hatching. They will remain with their parents for six months after leaving the nest. The raven can live a long time, especially in captivity or when protected; some ravens at the Tower of London lived for over 40 years. The life span in the wild is considerably shorter: usually ten to fifteen years.[citation needed] The oldest banded wild individual was thirteen years old.[citation needed]

Juveniles begin mating rituals at an early age, but will not mate before they are two or three years old. Aerial acrobatics, intelligent displays, and foraging skills are key performances in the mating display. Once mated, pairs tend to nest together for their entire lives, usually in the same location. Pairs must possess a territory before beginning nest building and reproduction, and thus, they fiercely defend their territory and its resources. The size of nesting territories varies depending on the density of food sources in the region. The nest is a cup constructed of branches and twigs held together by an inner layer of roots, mud, and bark. The interior is lined with softer materials such as deer hair. The nest is usually located in a large tree, on a rocky outcrop, or, more frequently, on old buildings or electricity poles. Females lay three to seven pale blue-green eggs spotted with brown. In most of its range, laying begins in late February. In colder climates, eggs are laid later; in Greenland and Tibet, they are laid in April. In Pakistan, laying takes place in December. Only the female incubates, and incubation lasts 18 to 21 days. However, the male may sit on top of the eggs, guarding them without brooding them. The parents will feed the fledglings 35 to 42 days after hatching. They will remain with their parents for six months after leaving the nest. The raven can live a long time, especially in captivity or when protected; some ravens at the Tower of London lived for over 40 years. The lifespan in the wild is considerably shorter, generally 10 to 15 years.[citation needed]

This species has a distinctive call, the crascitar: a deep, cavernous "rrok-rrok," which experienced observers find distinctive from that of other corvids. Its complex vocabulary includes a "knock-knock-knock," a dry, hoarse "kraa," a low, guttural croak, and several almost musical calls. Since cras means "tomorrow" in Latin, and they are typically carrion birds, they were often considered birds of ill omen, and it was in this light that Edgar Allan Poe composed his famous poem "The Raven," whose refrain is: And the Raven said, "Nevermore." Like other corvids, the great raven can imitate the sounds of its environment, including the human voice. It has a wide range of vocalizations. Observed calls include alarm calls, flight calls, and pursuit calls. The great raven also produces non-vocal sounds, including wing noises and beak crackling. Crackling was observed more often in females than in males. If a member of the pair disappears, the mate reproduces its calls, requesting its return.

A recent study also claims that crows are able to recognize different human voices, as well as the calls of birds of other species.

The greater crow has one of the largest brains of any bird species. It also displays several skills such as problem-solving, imitation, and intuition. An experiment designed to assess intuition and problem-solving featured a piece of meat tied to a string hanging from a horizontal perch. To reach the meat, the bird had to perch on the perch, pull the string in several steps, and hold the string at each step, thus shortening it. Four of the five passed the test, and the transition from no success (ignoring the food or simply not pulling the string) to consistent and predictable success (dragging the meat to the perch) occurred without apparent learning.[11] Crows have been observed directing other animals to work for them, for example, by calling wolves and coyotes to the site of a carrion. The canids then cut open the carrion, making it more accessible to the crows. They are also known to observe where other crows hide their food and remember these locations, allowing them to steal it. The great crow is known for stealing and hiding shiny objects such as pebbles, pieces of metal, and golf balls. One hypothesis is that young birds are curious about anything new and that their attraction to round, shiny objects is based on their resemblance to eggs. Adults lose this intense interest in the unusual and become neophobic. Recently, researchers have recognized that birds play. Young crows are among the most playful of all bird species. They have been observed gliding along snowdrifts, apparently for the sheer pleasure of it. They even play with other species, for example, playing cat and mouse with wolves and dogs. The crow is famous for its spectacular aerial acrobatics, such as looping.

The great raven is omnivorous and opportunistic: its diet varies depending on location, season, and what it finds by chance. For example, ravens nesting near sources of human-generated waste include a higher percentage of food waste in their diet; individuals nesting near roads consume more vertebrates that have been victims of roadkill; and individuals nesting far from these food sources consume more arthropods and plants. For example, on the Alaskan tundra, ravens obtain about half of their energy needs from predation (mainly small rodents, microtus) and the other half from scavenging (mainly caribou and ptarmigan carrion). Their plant diet includes cereals, berries, and fruits. They hunt small invertebrates, amphibians, reptiles, small mammals, and birds. However, a study conducted between 1984 and 1986 on the diet of great crows in southwestern Idaho (an agricultural region) revealed that grains were the main component of their diet, although small mammals, grasshoppers, bovine carrion, and birds were also consumed. They cache surplus food, especially food containing fat, like the Arctic fox. In winter, they may also associate with another canid, the gray wolf, as a kleptoparasite and follow it to feed on carrion. They may also consume undigested parts of animal feces and human food waste. Nest success is higher in individuals that use human waste as a food source.

A mature Greater Raven measures between 52 and 69 cm in length with a wingspan of 115 to 160 cm in Europe: 144-160 cm for the male and 124-138 cm for the female. Its weight varies from 0.7 to 1.7 kg, making it the heaviest of the passerines. Birds from colder regions such as the Himalayas and Greenland are generally larger, with a slightly larger bill, while individuals from warmer regions are smaller, with a proportionally smaller bill. The bill is strong, black, and slightly curved. The tail is relatively long, the neck is fairly thick, and the iris is dark brown. The plumage is generally black but has iridescent bluish and purple highlights. The throat feathers are elongated, and the base of the neck feathers is a pale grey-brown. The plumage of juveniles is similar to that of the adults but duller, and the iris is blue-grey. In addition to its large size, the great raven differs from the hooded crows by its stronger and thicker beak, throat feathers, and a lozenge-shaped tail, rather than almost straight like the hooded crow's.

The great raven has coexisted with humans for thousands of years, and in some regions it is so abundant that it is considered a pest species. Part of its success is due to its omnivorous diet; the great raven is extremely opportunistic, feeding on carrion, insects, food waste, grain, fruit, and small animals. Several remarkable displays of problem-solving have been observed in this species, suggesting that the great raven is highly intelligent.[3]

Throughout the centuries, the great raven has been the subject of myth, folklore, and representations in the arts and literature. In several ancient cultures—including those of Scandinavia, Ireland, Wales, Bhutan, the Northwest Coast of North America, Siberia, and Northwest Asia—it has been venerated as a god or a spiritual symbol.

The raven (Corvus corax), formerly known as the common raven by the Spanish Society of Corvids, is a passerine bird in the Corvidae family. Found throughout almost the entire Northern Hemisphere, it is the corvid species with the largest distribution area. However, the carrion crow (Corvus corax), smaller in size but very similar in external morphological appearance, is very abundant in its own range, so carrion crows are often confused with ravens. Along with the thick-billed raven, the raven is the largest of the corvids and probably the heaviest passerine; at maturity, the raven measures between 52 and 69 cm in length and weighs between 0.69 and 1.7 kg. Ravens generally live from ten to fifteen years, but some individuals have lived for forty years. Juveniles may travel in groups, but pairs remain together throughout their lives, each pair defending a territory. There are eight known subspecies that differ very little apparently, although recent studies have shown significant genetic differences between populations in different regions.