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Crows and Jays

General characteristics

The members of the crow family (Corvidae) are among the world's most intelligent birds. The family has recently undergone taxonomic expansion, brought about by evidence gathered through genetic testing, and now includes such diverse species as birds-of-paradise, orioles, and drongos. Crows and jays belong to the subfamily Corvinae. The corvids comprise 113 species in 25 genera, which include ravens, crows, jays, magpies, rooks, nutcrackers, and jackdaws. Corvids are passerine or perching birds and count among their numbers the largest of the passerines. Corvids vary considerably in size, ranging from the tiny Hume's ground jay, which is 7.5 in (19 cm) long and weighs 1.5 oz (45 g), to the thick-billed raven, which is 25 in (64 cm) long and weighs 53 oz (1.5 kg).

Corvids originated in the northern and tropical areas of the Old World. From there they spread to their current geographic range; they are found around the world and are found everywhere except in the high Arctic, Antarctic, the southern part of South America, and New Zealand. Corvids vary widely in size and appearance, particularly those species found in the forests of Central and South America and Southeast Aisa. There are 27 oriental genera, which experts consider strong evidence that the corvids first evolved in Asia and then spread north and east, across the Bering land-bridge, into North America and, eventually, to Central and South America.

Crows are large to very large, robustly built birds, with tails that are short or medium length. The tail and primary feathers are stiff. The bill varies in shape from species to species, but is relatively long, although it can be stout or slender. The feet and legs are very strong, with scales on the front of the toes and smooth skin on the back. Among the crows the plumage is black, black and white, black and gray or sooty brown, while jays can also be green, blue, gray, and chestnut. The males and females appear similar; that is, there is not the sexual dimorphism found in other birds such as pheasants and ducks, where the male is brilliantly colored and the female has dull plumage. Some species of jays and magpies have crests. Common to all the corvids is a tuft of bristles at the base of the beak, just above the nostrils and there are more bristles fringing the mouth.

The personality of crows and jays can be described as aggressive, intelligent, quarrelsome, and sometimes playful. The voice of a corvid, once heard, is not easily forgotten. They produce an astounding range of harsh or more musical calls, which are part of languages, researchers also discovered. The repertoire of the blue jay (Cyanocitta cristata), for example, includes high-pitched shrieks (usually aimed at intruders such as cats, owls, or humans; a cry of jeer-jeer; a ringing, bell-like tull-ull; a call that sounds like the word "teacup'; a rapid clicking call; a soft, lisping song; a sound like a rusty gate; and imitations of the red-tailed hawk, the black-capped chickadee, the northern oriole, the grau catbird, the American goldfinch, and eastern wood pewee. Some species can even imitate human speech.

This range of imitative ability is common to several members of the crow family, and is both evidence of the family's intelligence and part of the reason these birds figure so prominently in human fiction. Experiments with captive common, or American, crows (Corvus brachyrhynchos) have proved the birds have excellent puzzle-solving abilities, can count up to three or four, have good memories, and can quickly learn to equate certain sounds or symbols with food. Caged jackdaws that were exposed to a 10-second burst of light accompanied by a four-minute recording of jackdaw distress calls, followed by two minutes of silence and darkness, soon learned to peck a key that shut off the light and the recording. A captive blue jay used a tool (a scrap of newspaper from the bottom of its cage) to reach a pile of food pellets that lay outside the cage, just out of reach of its beak. Most interesting, several other captive jays who watched this one method of problem solving soon used it too.

Although these captive experiments provide much information, observations of wild corvids provide even better evidence of the corvids' intelligence. In Norway and Sweden, springtime fishermen make holes in the ice and drop their fishing lines through them into the water. Hooded crows have been seen picking up the line and walking backward as far as they can, pulling the line out of the hole. The crow will do this as often as it needs to bring the end of the line to the surface, as well as the bait or the hooked fish—which the crow then devours.

The corvids are wary as well as smart. One bird researcher noted that blue jays' intelligence is the key to their not falling victim to the prowling cats that kill so many other species of bird. Crows also show signs of coming to one another's aid; the cawing of a common crow will bring crows from everywhere around, ready to mob the predator.

Crows live in varied habitats, including forests, grasslands, deserts, steppes, farms, and urban areas. They are mostly tree-dwelling, but the ground-jays have adapted to a life on the ground so much that they will run from a threat rather than fly.

They are highly gregarious birds. A flock may consist of as few as six to as many as a few hundred birds. Within the flock is a social hierarchy, particularly among the crows, the pinyon jays, scrub jays, and Mexican jays. However, mated pairs nest on their own. Corvids are generally aboreal nesters, building a nest of twigs lined with soft materials, although some species nest in holes or build domed nests. The female incubates the eggs (two to eight, depending on the species) alone for 16 to 22 days (again, the length of incubation depends on the species), and her mate feeds her while she does so and helps feed the young after they are born. Corvids do not carry food in their beaks, but rather in their throat or in a small pouch within the chin, under the tongue. Although the members of the crow family are known to be raucous, they become secretive near their nests, drawing as little attention as possible to themselves and their nestlings.

Young common crows fledge between 28 and 35 days old; among the family the nestling period ranges from 20 to 45 days. Although captive crows have been known to live 20 years or more, most wild corvids do not live that long.

A Steller's jay (Cyanocitta stelleri) in California. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission.

The diet of crows and jays is varied both among and within species. The American, or common, crow eats insects, spiders, crustaceans, snails, salamanders, earthworms, snakes, frogs, the eggs and chicks of other birds, and carrion. The crows will crack the shells of clams, mussels, and other bivalve mollusks by picking them up, flying with them to a height, and then dropping them to rocks below (herring gulls and crows were seen practicing this tactic at the same time, but the gulls dropped the mollusks onto the mud; the crows figured out much sooner that aiming for the rock was a better, more certain, method). The corvids are not solely carnivorous, however; the blue jay eats about three times as much vegetable matter—including acorns, corn, berries, currants, sorrel, and even cultivated cherries—as it does animal matter. Blue jays have been known to eat mice, small fish, and even bats. Another common North American crow, the fish crow of the eastern United States, also eats shrimp, fiddler crabs, crayfish, and turtle eggs.

Most wild corvids that have been studied have been seen hiding food for future use. Small prey items, such as insects and earthworms, are not usually hidden, but unexpected "bonuses" are hidden away in small holes or under fallen leaves, although hiding places in trees or buildings will also be used. The Canada jay would be unable to recover ground-buried food during the harsh northern winter, so instead hides food in pine and fir trees, sticking it to the branches with saliva (this species has developed accordingly large salivary glands for this task).

Ravens and crows have both been reported to hide some of a large amount of food before settling down to eat the remainder. The apparently excellent memories of crows serve them well in rediscovering these food caches, although success varies among species. Many of the acorns hidden by blue jays in the fall are never recovered. The nutcrackers, on the other hand, have been known to recover 70% of the seeds they store.

Their natural enemies include owls, eagles, and buzzards, and they have had a long-running battle with human beings. In the United States, common crows are fond of corn and other cultivated crops, and as a result have been shot at and poisoned. The house crow of India—a tremendously successful commensal species which has tied its life so tightly with that of man that its survival alone would be unlikely—has been destroyed in several places because its large flocks caused it to be considered a health threat.

Despite this animosity, most cultures have tales to tell about the corvids. Ravens figure prominently in Inuit legend. Two ravens, Huginn and Munnin, were the companions of the Norse god Odin. A legendary Celtic warrior god named Bran was also accompanied by a raven, and the bird is known by his name (Cigfran) in Celtic Welsh, Cornish, and Breton. In Cornwall, legend has it that the raven and another corvid, the red-billed chough, hold the spirit of King Arthur, and woe to he who harms either of these birds! From far back the raven has been associated with death, particularly with foretelling it—perhaps because of its close association with the Vikings, this raven-death association was particularly strong in western Europe.

And the legends are not all just in the past: even in the late twentieth century captive ravens are kept in the Tower of London. The belief is that when the last raven leaves it, the monarchy will fall.

Despite the success of the family as a whole, at least 22 species of corvids are endangered, including the Hawaiian crow (Corvus tropicus) and the Marianas crow (C. kubaryi).

F. C. Nicholson

Additional topics

Science EncyclopediaScience & Philosophy: Cosine to Cyano group