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Animal Detail ViewՄանրամասն` նրանց մասին

27.02.2012

Common Raven (Corvus corax)


Scientific classification:

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Aves
Order: Passeriformes
Family: Corvidae
Genus: Corvus
Species: Corvus corax

 

Description

The Common Raven is the biggest and most spread species of the Corvid family in Europe and the Northern Hemisphere. It achieves a length up to 69 centimeters and an average weight of 1157 gram. There is no sexual dimorphism but females may be slightly smaller and lighter than males. All Common Ravens have a black metallic glaring plumage and a wedge-shaped tail. Their throat is adorned with a feather ruff, the so called “hackles”, which is used for social communication. They have strong claws and bills.
Feathers of juvenile birds are brown-black and do not shine. They have no hackles which develop not until the birds achieve an age of three years.
In wild the longest lifespan of a Common Raven was recorded with 13 years. In captivity they can reach a much higher age up to 44 years.

Range and Habitat

The Common Raven has one of the largest distribution ranges of any bird species. It occurs in the Holarctic, in India and the Himalayas, in temperate habitats of Eurasia and North America, in the Near East as well as next to the deserts of North Africa and some islands in the Pacific Ocean.

Preferred are regions with open-landscape, but the species can be found in many types of habitat except rainforests. They live in the treeless tundra, at coasts and cliffs, in mountain forests, deserts and scrubby woodlands. Some subspecies are mostly found in wild areas whereas some are used to live near humans and in landscapes shaped by human impact.

Nests are built on cliffs or in trees but in urban areas also power lines and towers can be nesting sites.

Distribution range of the species includes Armenia

Behavior

All members of the Corvid family, including Common Ravens, Crows, Jays, and Magpies are famous for their intelligence and complex social behavior. They are not only able to find solutions to solve problems but they are also extremely playful. For example there are reports about ravens which are observed sliding down snow banks on their backs and playing tag, hide-and-go-seek and stick catching (while flying!).
Ravens form monogamous breeding-pairs but there are also non breeding individuals as it took sometimes three to four years until a Common Raven finds his/her mate. Out of the reproduction period Common Ravens can often be observed in large flocks. Except small movements because of unfavorable weather, the species is not migratory.
Vocalization is a very important part of their communication. A broad variety of calls is used in different situations as well as non-vocal sounds as bill snapping and wing whistles. All in all 15 to 33 different types of vocalizations are reported which, for example, occur as alarm calls, chase calls or comfort screams. The ability to mimic sounds is guessed but not proved.
Communication is also provided through different physical displays. For instance, pairs chase intruders out of their territory. Ravens were also observed to use gestures to communicate for example by offering twigs or stones to conspecifics to initiate a relationship.

Diet

Predominately Common Ravens are omnivores which mean that their diet includes animals as well as vegetable matters. Carrion attracts ravens but they feed also on insects or the afterbirth of large mammals. Grains, fruits, acorns take over the vegetarian part. Different types of human garbage are an additional food source. The food is picked from the ground and can be stored.

Reproduction

Much of Common Raven’s behavior is related to mating and reproduction. Juveniles begin to court at a very early age, but may not bond for another 2-3 years. Aerial acrobatics and displays of intelligence and ability to provide food are key behaviors of courting ravens. Common Ravens are monogamous and a breeding pair stays in its territory most probably for its entire life time. They construct enormous nests of twigs and other found objects that can measure more than one meter across. Copulation is accepted when the female invites the male by dropping wings and shaking its tail.
Most eggs are laid in March or April, even if the breeding season varies from region to region. The 3 to 7 eggs are incubated by the female for 20 to 25 days. Rearing the nestlings by regurgitating food and water stored in throat pouches is the duty of both parents..
5 to 7 weeks after hatching the little Common Ravens leave the nest and some weeks later may leave the family or sometimes stay with their parents. They achieve sexual maturity at the age of three years.

Conservation Status

The accusation that Common Ravens often prey on lambs and crops caused a high persecution rate. Whether poisoned, shot or captured in traps - often the birds were killed by humans to protect other species or because they were simply perceived as competitors for example by hunters. At some places hunting of Common Ravens reached such a high extent that the birds get almost locally extinct. Fortunately some of these populations have recovered due to strict protection laws. Altogether the species is very widespread and the population size seems to be quite large and stable. Therefore it is evaluated as Least Concern on the IUCN List of Threatened Species.

Ecosystem Roles

Only few animals actually try to prey upon ravens because they are quite capable of defending themselves. Because they scavenge garbage, steal dog food, and try to snatch bait from traps, ravens living near settled communities may be harassed or persecuted by humans who view them as pests. Sometimes raven nestlings are caught by large hawks and eagles. Adult Common Ravens are quite successful at defending their nests and offspring by chasing predators away. Positive for humans and the ecosystem is the fact that ravens feed on carrion. While removing the carcasses of dead animals they help to prevent diseases. Furthermore they control populations of their prey as other birds, mammals and insects. Humans may feel negatively affected by ravens because they eat grains, nuts and other agricultural plants or reduce livestock.

Ravens in culture

Humans were always fascinated by these large, black and obviously intelligent birds. Thus the raven has a place in many cultures and legends. Often the bird was linked with gods as in Siberia or northeast Asia. In the Norse mythology Odin is referred to as the “raven god” as he is always accompanied by the ravens Huginn and Muninn. Odin sends these two birds off around the world at daybreak, to bring him the daily news.

In several parts of the Bible’s Old Testament the raven is also mentioned. For example it was the first animal that was released from Noah's ark though it showed disobedience by failing to return to the ark after being sent to search for land. In the British Isles the raven was a symbol of the Celts. Especially in Western traditions ravens were perceived as being dark messengers of doom, diseases and death as well as a symbol for black magic and witchcraft (very similar to black cats!). Maybe this negative reputation was connected to its black color or because of the fact that ravens feed on carrion. More generally one can say that in many cultures the raven is a messenger and a trickster which can cross the border between this world and the after world.

Many famous poets and writers used the raven as a symbol or metaphor among them William Shakespeare, Edgar Allen Poe or J. R. R. Tolkien.

Short Facts

·         The Common Raven is the national bird in Bhutan.

·         Worldwide Common Ravens are one of the most widespread bird species in nature. This is possible because it has a very flexible diet and can learn very fast.

·         A legend tells that England would not fall to a foreign invader as long as there are ravens at the Tower of London.

·         The raven is the largest species of songbird and largest all-black bird in the world.

 



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