Throughout human folklore, the raven has been closely associated with death, frequently regarded by early civilisations as an ill omen and portent of mortality, yet it has also occupied a more complex symbolic role. In Norse mythology, the raven served as a loyal companion and messenger to Odin, the god of war and death, who was himself often known as Hrafngud, the Raven God. Literary tradition reflects this duality: the eponymous protagonist of Charles Dickens's Barnaby Rudge is constantly accompanied by his pet raven, Grip. In Britain, enduring legend holds that the security of the kingdom depends upon the continued presence of ravens at the Tower of London; apocryphal accounts claim that when Charles II was advised to remove the birds -- allegedly because they interfered with the work of the astronomer John Flamsteed in the White Tower -- he was warned that doing so would have catastrophic consequences for the monarchy. Linguistically, the word raven derives from the Old English hræfn or ræfen, while the species' binomial nomenclature draws upon the Latin corvus and the Greek corax, both meaning raven.
Eleven subspecies are tentatively recognised, albeit with some authors arguing as few as four - the type, Corvus corax corax, is found in the UK.
Size: The largest of the corvids, ravens stand 30-40 cm (12-16 in.) tall, measure up to 70 cm (28 in.) in length, and have a wingspan of 115-153 cm (46-60 in.). In the literature there is considerable variation in recorded weights for mature birds -- from 690 g to 2.2 kg (1.5-5 lbs) -- with habitat and location important considerations. The smallest birds seem to be those from North Africa (subspecies tingitanus), while the largest hail from the Himalayas (subspecies tibetanus).
Appearance: Very large birds, matching or exceeding the size of common buzzards in most regions, with jet black plumage that sheens green or bluish-lilac in direct sunlight. The beak/bill is very thick, much more so than other corvids, and its upper section covered with fine feathering for half its length (nasal bristles). Loose feathers around the throat can be expanded as a "beard". Indeed, the feathers on the head, chin, and throat can be expanded to exaggerate the size of the bird's head, particularly while calling. The long tail forms a diamond shape while the bird is in flight, differentiating it from the blunt and curved in-flight tail of the carrion crow and rook, respectively. The feet and legs are black. Moulting runs from July to October in Britain.
Distribution: A very widely distributed species, ravens range throughout the Holarctic, from Arctic and temperate habitats in North America and Eurasia to the deserts of North Africa, and several Pacific islands. In Britain the species is similarly widespread away from eastern and central-eastern England and eastern Scotland. The BTO have reports of non-breeding sightings from East Anglia and eastern coastal England, but these are sparse and there are no breeding records despite a significant increase in the population since the mid-1990s. Eastern England appears suitable for ravens and there are historic breeding records from here, so their continued absence is unexpected, although some sources suggest the birds' colonisation and persistence here is prevented by estates with gamekeeping and farming interests. Ravens are found throughout Ireland. Globally, the species is found from sea level up to 6,350 m (20,600 ft.) on Mount Everest.
Habitat: A habitat generalist to the point where the concept of habitat seems almost redundant - found from the most isolated, barren, craggiest country, including cliffs and moorland, to lowland woodland, farmland, and wetlands. Can tolerate extremes of temperature, from the Arctic to Death Valley. Typically nest on craggy outcrops and sea cliffs, occasionally in trees and on tall or pylons buildings.
Longevity: The longest-lived raven held at the Tower of London, named Jim Crow, survived to 44 years old, but the birds here are subject to veterinary care provided by the Zoological Society of London and it's unlikely wild birds would reach this age. Indeed, most wild birds probably survive a maximum of 10 to 15 years, although EURING, the coordinating organisation for European bird ringing schemes, gives the oldest wild-rung raven, a bird from Norway, as 23 years and 3 months.
Sexing: Arguably impossible visually, particularly at distance, owing to very little sexual dimorphism. Males tend to be larger than females and may have somewhat more robust bills, slightly larger head profiles, and longer, shaggier throat feathers. Some observers have suggested males have a larger throat pouch that extends further down the neck than female during the nesting season, but I'm not aware of any empirical data confirming this.
Activity: A diurnal and crepuscular species, ravens are active from dawn to dusk. One radio-tracking study from Idaho found much of their time was spent resting or in communal roosts, while feeding accounted for 10-14% of daytime hours, flying 13%, and walking around on the ground 11%.
Territory/Home Range: Where pairs hold a territory it will be aggressively defended from other ravens year-round, but not all birds are territory holders and many join flocks of varying size that move widely. Even territory-holding birds may forage over considerable distances, with one North American record covering 1,800 sq-km. A study in Wales, by contrast, found birds tended to forage within 1.5 km of the nest site. Birds may leave their territory to feed with other pairs and solitary birds at rich food sources, particularly during the winter.
Diet: Omnivorous, although notoriously wary of novel food sources - one study in Yellowstone found ravens attended all wolf kills, feeding alongside the canids, but avoided carcasses left by the research team. Part of their establishment in human folklore comes from their appearance on battlefields where they fed on human corpses. Typically, ravens will catch small mammals and birds but will also take invertebrates (especially insects, spiders, and shoreline molluscs) and plant matter, notably cereals, nuts, and fruit. Rabbit and hare fur is often reported from pellets, but these may be scavenged roadkill. Frequently observed scavenging, particularly on dead livestock in upland areas and on road killed deer. May take larger birds, including wading birds up to the size of curlews, which has raised concerns that increasing/recovering raven populations may detrimentally impact local wader populations. A 2010 study found no significant negative spatial or temporal relationships between ravens and any of the five species of waders studied, however. Will take eggs from nests as well as human refuse. Surplus food is cached (stored), as are other objects of value (e.g., toys) by captive individuals.
Reproduction: An early nesting species, monogamous with life-long pair bonds. Nest construction may begin as early as mid-February in the UK, and birds reusing existing nests may lay during the first week of February and have full clutches by the end of the month. Most females in Britain and Ireland will be incubating by the end of March. Nests are deep, composed of large sticks, and constructed in inaccessible spots such as crags, cliff faces, and occasionally in tall trees, pylons, or bridges. Nests are lined with softer materials such as moss, wool, deer fur, grass, and heather – mud is occasionally also used. A pair may have several nests in their territory and cycle between them through successive breeding seasons. Eggs measure about 50x34 mm (2x1.3 in.) and are pale pink to off-white in colour, spotted and blotched with brown/olive markings. Clutches are generally produced between February and March, with 4 to 7 eggs laid at one day intervals such that the clutch is normally complete in 8-14 days.
Incubation typically starts when the clutch is complete, but may start sooner, and is carried out entirely by the female, who is provided with food and water (carried in the throat pouch) by the male. Incubation takes 17-21 days and chicks hatch naked, blind, pot-bellied and entirely dependent on their parents. The male remains the sole provider of food, although both parents may feed the brood. Fledging happens around 45-50 days (6-7 weeks) old and the parents will routinely leave food on the ground to encourage the young away from the nest. The family remains together for most of the summer before the young are chased away ahead of the next breeding season. Age of first breeding is unknown but assumed to be at least 2 years.
Only a single brood will be raised in any given year, but loss of a clutch will usually result in an attempt at rebreeding about 2 weeks later.
Behaviour & Sociality: A supremely intelligent and highly social species, ravens have a wide behavioural repertoire that includes flying upside down; apparently a purely playful activity. Large flocks numbering up to 2,000 birds reported in parts of North America, but usually found either solitarily, in pairs, or small groups. Non-breeders appear to associate in small flocks of 50-60 birds and may cover several hundred square kilometres. Pairs will preen one another (allopreening) and engage in beak-holding (one member of the pair holds the bill of their partner in their own beak). Well-established hierarchy, with paired birds holding higher positions than single individuals. Communally roosting birds may assemble near roost ahead of sunset to play (chasing and aerobatics) before settling. Fighting may ensue at food sources, and there are records of flocks ousting territory holders and destroying nest sites, scattering sticks over a wide area. Various vocalisations have been reported – primarily a loud, abrupt, echoing cronk or prruk, typically issued in a series of three or four repetitions. A metallic tonk is known, along with a range of clicks, rattles, and quiet musical notes. With practice birds can mimic other animals, including humans. Generally wary of humans where they're shot but can be remarkably bold in areas with little or no persecution.
Threats/Conservation: Young, unguarded chicks are probably at risk from several predators, including other corvids, gulls, and foxes, but it's unlikely adults are vulnerable to much other than humans, weather, and disease. Potentially prey to Golden eagles (Aquila chrysaetos) and ravens appear to nest at least 1 km (0.6 mi.) from active eyries. Buzzards (Buteo buteo) appear dominant at carcasses and there's one report of remains of a raven chick at a Red kite (Milvus milvus) nest, although this may have been scavenged given there's a report of a pair of ravens killing an adult male kite. The raven is fully protected in law by the Wildlife and Countryside Act 1981 (as amended). The Act offers the species general protection, meaning it is illegal to kill a raven, although some conservation charities maintain illegal persecution persists, notably on gamekeeping and lambing estates. The Act also contains provision for issuing licences to control ravens, with strict conditions.