Common Raven, Corvus corax
Note: this post, while published, is a work in progress, as are all posts in this series, My Photo Life List. My goal is to photograph every species of bird that is seen on a regular basis here in Michigan, working from a list compiled by the Michigan chapter of the Audubon Society. This will be a lifelong project, that I began in January of 2013, and as I shoot better photos of this, or any other species, I will update the post for that species with better photos when I can. While this series is not intended to be a field guide per se, my minimum standard for the photos in this series is that one has to be able to make a positive identification of the species in my photos. The information posted here is from either my observations or the Wikipedia, the online free encyclopedia, however, I have personally shot all the photos appearing in this series.
Common Raven, Corvus corax
The Common Raven (Corvus corax), also known as the Northern Raven, is a large all-black passerine bird. Found across the Northern Hemisphere, it is the most widely distributed of all corvids. There are at least eight subspecies with little variation in appearance, although recent research has demonstrated significant genetic differences among populations from various regions. It is one of the two largest corvids, alongside the Thick-billed Raven, and is possibly the heaviest passerine bird; at maturity, the Common Raven averages 63 centimetres (25 inches) in length and 1.2 kilograms (2.6 pounds) in mass. Common Ravens can live up to 21 years in the wild, a lifespan exceeded among passerines by only a few Australasian species such as the Satin Bowerbird and probably the lyrebirds. Young birds may travel in flocks but later mate for life, with each mated pair defending a territory.
Common Ravens have coexisted with humans for thousands of years and in some areas have been so numerous that people have regarded them as pests. Part of their success as a species is due to their omnivorous diet; they are extremely versatile and opportunistic in finding sources of nutrition, feeding on carrion, insects, cereal grains, berries, fruit, small animals, and food waste.
A mature Common Raven ranges between 56 and 78 cm (22 to 30 inches) in length, with a wingspan of 100 to 150 cm (40 to 59 in). Recorded weights range from 0.69 to 2 kg (1.5 to 4.4 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. The bill is large and slightly curved, with a culmen length of 5.7 to 8.5 cm (2.2 to 3.3 in), easily one of the largest bills among passerines (perhaps only the Thick-billed Raven has a noticeably larger bill). It has a longish, strongly graduated tail, at 20 to 26.3 cm (7.9 to 10.4 in), and mostly black iridescent 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 good-sized, with a tarsus length of 6 to 7.2 cm (2.4 to 2.8 in). Juvenile plumage is similar but duller with a blue-grey iris.
Apart from its greater size, the Common Raven differs from its cousins, the crows, by having a larger and heavier black beak, shaggy feathers around the throat and above the beak, and a wedge-shaped tail. In flight the feathers produce a creaking sound that has been likened to the rustle of silk.
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 vocalization 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, Ravens 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.
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. 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.
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 before they can eat themselves. 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.
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.
Linguist Derek Bickerton, building on the work of Bernd Heinrich, has recently argued that ravens are one of only four known animals (the others being bees, ants, and humans) who have demonstrated displacement, the capacity to communicate about objects or events that are distant in space or time from the communication. Young, unmated Common Ravens roost together at night, but usually forage alone during the day. However, when one discovers a large carcass guarded by a pair of adult ravens, he will return to the roost and communicate his find. The next day, a flock of young ravens will fly to the carcass, and chase off the adults. Bickerton argues that the advent of linguistic displacement was perhaps the most important event in the evolution of human language, and that ravens are the only other vertebrate to share this with humans.
One experiment designed to evaluate insight and problem-solving ability involved a piece of meat attached to a string hanging from a perch. To reach the food, the bird needed to stand on the perch, pull the string up a little at a time, and step on the loops to gradually shorten the string. Four of five Common Ravens eventually succeeded, and “the transition from no success (ignoring the food or merely yanking at the string) to constant reliable access (pulling up the meat) occurred with no demonstrable trial-and-error learning.” This supports the hypothesis that Common Ravens are ‘inventors’, implying that they can solve problems. Many of the feats of Common Ravens were formerly argued to be stereotyped innate behavior, but it now has been established that their aptitudes for solving problems individually and learning from each other reflect a flexible capacity for intelligent insight unusual among non-human animals.
Common Ravens have been observed to manipulate other parties into doing work for them, such as by calling wolves and coyotes to the site of dead animals. The canines open the carcass, leaving the scraps more accessible to the birds. They watch where other Common Ravens bury their food and remember the locations of each other’s food caches, so they can steal from them. This type of theft occurs so regularly that Common Ravens will fly extra distances from a food source to find better hiding places for food. They have also been observed pretending to make a cache without actually depositing the food, presumably to confuse onlookers.
Common Ravens are known to steal and cache shiny objects such as pebbles, pieces of metal, and golf balls. One theory is that they hoard shiny objects to impress other ravens. Other research indicates that juveniles are deeply curious about all new things, and that Common Ravens retain an attraction to bright, round objects based on their similarity to bird eggs.
In recent years, biologists have recognized that birds engage in play. Juvenile Common Ravens are among the most playful of bird species. They have been observed to slide down snowbanks, apparently purely for fun. They even engage in games with other species, such as playing catch-me-if-you-can with wolves, otters and dogs. Common Ravens are known for spectacular aerobatic displays, such as flying in loops or interlocking talons with each other in flight.
They are also one of only a few wild animals who make their own toys. They have been observed breaking off twigs to play with socially.
On to my photos:
This is number 144 in my photo life list, only 206 to go!
That’s it for this one, thanks for stopping by!