The Revered, Reviled Crow Clan
by Howard Youth
For centuries, a dark specter haunted the bloody battlefields of Europe. Waiting to feast on the dead, common ravens lined up at bloody clashes between invaders and invaded, tribes and kingdoms. War-weary observers could not ignore the jet-black scavengers, with their four-foot-wide wingspreads and cross-shaped flight profiles. Ravens, not surprisingly, were branded harbingers of bad luck, or death.
Away from the carnage, common ravens (Corvus corax) also coasted into folklore, legend, and language, strongly hinting that these creatures and their 100-plus brethren in the family Corvidae are not your average birds. Two ravens, Hugin (Thought) and Munin (Memory), rode the broad shoulders of the Norse god Odin. In Inuit legend, the raven became creator and trickster. In the Bible, Noah sent not only a dove but also a raven to seek land, as did many ancient mariners. Tame ravens still stroll within the Tower of London's walls, where for centuries they've been sequestered as guardians against invasion.
One reason why ravens, crows, jackdaws, rooks, magpies,
treepies, choughs, nutcrackers, and jays stand out is
that they have above-average brains—proportionately,
they possess the largest cerebral 
hemispheres
of the feathered set. Plucky, crafty, curious, social,
vocal, and adaptable, corvids, as family members are
known, are among our most familiar yet enigmatic neighbors.
On all continents save Antarctica, they flourish in
backyards and wilderness, although more than 20 species
barely hang on within shrinking habitats. Ethiopia's
thick-billed raven (Corvus crassirostris), bigger
than a red-tailed hawk, is the world's largest songbird,
while the dun-colored Hume's ground-jay (Pseudopodoces
humilis) of the Tibetan plains is the smallest family
member. In between lies a broad spectrum of glossy,
splashy, and plume-tailed characters.
The Smart and the Damned
Are ravens the most intelligent of birds? Many think
so. But comparing ravens with other birds such as parrots
is "…like saying what is better, apples or
oranges," says Bernd Heinrich, a field biologist
and University of Vermont biology professor who for
the last 16 years has studied the private lives of wild
and captive common ravens. In his book, Mind of the
Raven, Heinrich writes, "I have become skeptical
that the interpretations of all ravens' behavior can
be shoehorned into the same programmed and learned responses….Ultimately,
knowing all that goes on in their brains is, like infinity,
an unreachable destination."
After widespread persecution and decline over the last century, common ravens are rebounding. They nest on transmission towers and telephone poles and dine at landfills, on roadkills, and even on threatened species, including the eggs and young of desert tortoises (Gopherus agassizii), least terns (Sterna antillarum), and snowy plovers (Charadrius melodus). In the eastern U.S., the raven rebound has been less steady than in the West. Locally, these graceful birds can be easily seen in Shenandoah National Park and other parts of the Appalachians. A few pairs breed at and around Sugarloaf Mountain in Frederick County, Maryland, from which visitors, and most likely the ravens, can see downtown Washington, D.C., on a clear day.
While ravens stick to the outskirts of many cities, other large black corvids thrive within them. Each region seems to have one or two super-abundant species. "The [American] crow is the bold bad swashbuckler of the avian world," wrote Bert Popowski in his 1946 book Crow Shooting, a call-to-arms against crows, which he castigated for destroying desirable gamebirds and vacuuming up crop fields of their tender shoots. (While crows do take young birds and eat some crops, they also eat many pest insects.) Even Popowski had to admit that much of the "problem" with crows stemmed from their adaptability and wiles. He quotes the great naturalist Henry David Thoreau, who wrote "…if men had wings and bore black feathers, few of them would be wise enough to be crows."
When Popowski's book was published, crows were under constant fire: "There is no state in which the crow is not listed as a varmint bird, making it a favorite out-of-game-season target for both rifle and shotgun enthusiasts." Many states offered bounties. Roosts were sometimes blown apart with dynamite. Since the mid-1970s, however, crow hunting has been regulated. The birds are now treated as native birds instead of worthless pests that can be killed indiscriminately. Regardless, hunting does not seem to have much impact on crow populations, which keep growing along with the human population.
In most urban and suburban areas of North America, American crows (Corvus brachyrhynchos), ravens, or magpies (Pica pica) are among the most familiar birds. Their trash-scavenging, nest-raiding, pest-eating habits are mostly ignored, or sometimes greeted with half-hearted scorn (unless large, messy roosts pop up where people live, work, or shop, in which case scorn turns to rage). Overall, crows are at times persecuted but usually tolerated. In India, for example, house crows (Corvus splendens) and jungle crows (Corvus macrorhynchos) work alongside cows and pigs to clean the streets of trash. Crow experts Steve Madge and Hilary Burn wrote in their 1994 book Crows and Jays that the house crow is "possibly the only bird species totally dependent upon man for its existence." British ornithologist Derek Goodwin, in his book Birds of Man's World, wrote that the close union between house crow and human may have emerged because both species preferred the same habitat and because "no part of [the crow's] original home is now not overrun by human beings!"
Such dependence seems to assure a bright future for this bird. During my two years living in Madras, India, I daily saw both house and larger jungle crows riding on the backs of pigs, dining on watermelon rinds and other trash, ducking in and out of bustling train station platforms, or snatching morsels through open windows. These birds took advantage of all available amenities. House crows also have what you might call wanderlust. They regularly hitchhike on ships, no doubt to find food. From time to time, birds stay onboard ships as they cruise out of Indian, Pakistani, and Sri Lankan harbors. Satellite breeding populations now inhabit port towns in the Middle East, in various Asian sites including Singapore, in East Africa, and even in Mozambique and Durban, South Africa. Shipboard stowaways have turned up as far away as Australia, Japan, and at least twice in the United States. It seems the house crow is a strong candidate for the title of the dandelion of corvids.
Fancy, and Not So Fancy, Feasts
Corvids use their guile and versatile, strong bills
to procure an amazing assortment of foodstuffs. In some
species, such as many jays, vegetable matter makes up
75 percent or more of the diet, while ravens and others
are consummate carnivores. Consider the typical menu
sought by the plush-crested jay (Cyanocorax chrysops),
South America's most widespread corvid. This gaudy bird
flashes through the subtropical and tropical forest
in noisy foraging flocks, following swarming army ants
that kick up panicked insects and small lizards, plucking
ripe berries, snatching an occasional wild bird egg
or chick, and, at the forest edge, picking up table
scraps and crop seeds.
Other corvids have far more specialized tastes. For instance, the ranges of the western U.S.'s pinyon jay (Gymnorhinus cyanocephalus) and Eurasia's northwestern populations of nutcracker (Nucifraga caryocatactes) match almost exactly the ranges of their favored food plants, pinyon pine and spruce, respectively. But even these birds indulge in other birds' nestlings and eggs, insects, and a variety of other seeds--especially during nesting season or in times of food shortage.
Of course, crows and ravens are well known as trash eaters, common loiterers of street and landfill. Mount Everest explorers even found yellow-billed corvids called alpine choughs (Pyrrhocorax graculus) scavenging kitchen scraps at 27,000 feet. In the Alps, many skiers now find these high-altitude birds loitering around resorts for the same reason.
There seem few limits on what crows can learn in their quest for food. In Finland, hooded crows (Corvus corone cornix) learned to pull up, bill to foot to bill, the ice fishing lines left by fishermen to procure fresh catches. In 1996, New Zealand biologist Gavin R. Hunt documented New Caledonian crows (Corvus moneduloides), birds unique to that far-flung Pacific archipelago, carefully snipping rigid leaf pieces and fashioning them into two types of tools. The crows carried these tools with them as they flew to feeding areas, where they used hooked and narrow-tipped tools to fish out insects from hard-to-get spots. This discovery sparked debate over whether the birds' tool making was standardized, a manufacturing feat generally only attributed to humans. While no one seems likely to step up and claim that crows are more intelligent than chimpanzees (Pan troglodytes)—which catch termites and ants using modified but not standardized twigs and stems—the discovery marks a watershed in animal tool use.
The late Indian bird expert Salim Ali wrote of the house crow: "Revels in puckish antics such as playfully tweaking tails of other birds, or ears of sleeping cow or dog, or toes of flying foxes hanging on their diurnal roosting trees, with no apparent object other than to enjoy their annoyance and discomfiture!" Common raven pairs often perform similar stunts with eagles, with food acquisition being the primary goal. One bird tugs a tail feather while the other darts in to steal the raptor's fish or other prize meal. They even use similar tactics with coyotes (Canis latrans) and gray wolves (Canis lupus). It is easy to see how play and food acquisition go hand in hand with corvids, the artful dodgers of the bird world.
That's not to rob the corvids of their fun. There is plenty of evidence that crows play when not seeking food. They'll swing upside down to hang from perches, and drop objects and fly down to snatch them. Common ravens have been seen sliding down snow banks on their backs—clearly not food-seeking behavior. Whether or not play is strictly a means of honing certain survival skills is something I'll leave for the experts to puzzle over. Clearly, a wide range of skills benefits birds that make their living off of the trappings of our civilization or food provided by other creatures.
Once food is found, corvids do not always wolf it down.
Most corvid species hoard food, at least from time to
time. This helps them survive and even nest during lean
times. Clark's nutcrackers (Nucifraga columbiana),
for instance, may tuck 30,000 pine seeds into the 
ground
from late summer to fall in preparation for winter.
Meanwhile, blue jays (Cyanocitta cristata) and
Eurasian jays (Garrulus glandarius) are famed
for burying acorns. Any forgotten larder often shoots
up as tender young saplings the next spring. Some species
carry their booty in throat pouches, which they empty
when they reach their hiding places. The Clark's nutcracker
model holds as many as 90 pine seeds.
A Family Affair
Ravens, which may live up to 30 years, and many crows
and magpies mate for life, while most jays seek new
mates each breeding season. Unlike cardinals, orioles,
and many other familiar songbirds, corvids are monomorphic—males
and females have similar coloration. This, of course,
does not keep these birds from breeding. Pair bonds
grow through bobbing courtship displays, feeding and
bill-tapping rituals, swooping and diving flights, mutual
preening, and special vocalizations. (Ravens have at
least 30 documented calls, crows more than 20—and
some of these are only heard during courtship.)
Many species build bulky, stick-jumbled nests, which are usually cupped and in some cases domed, as in those made by some magpies. In most species, both sexes share nest-building duties. Females generally incubate an average of four to six eggs, but when it comes to feeding young, both parents usually share the work. Often, males also feed incubating females.
While some corvids, notably Eurasia's rooks (Corvus frugilegus), nest colonially, most set up defended territories and go it alone. However, the nesting pair, depending upon the species, is not always completely alone. Biologist Lawrence Kilham, studying American crows on a Florida ranch, found that these birds, unlike other known crows (except occasionally the northwestern crow, Corvus caurinus, of the Pacific Northwest), often breed cooperatively. Yearling birds assist adults at all nesting stages, helping to build nests, spot predators, and feed incubating females and young. "Remaining on natal territory gives juveniles and yearlings a chance to learn which predators are most dangerous, where to find food in various seasons, and other aspects of life important to survival, at less risk than if they were on their own," writes Kilham in his book The American Crow and the Common Raven.
Some jays also do this. Nesting Florida scrub jays (Aphelocoma coerulescens), endemic to the Sunshine State's stunted oak woods, are assisted by one to six young helpers. These assistants, previous nestlings, apparently help guarantee better survival rates for the next generation, while getting valuable life experience themselves. Cooperative breeding has also been found in azure-winged magpies [see "Cave Secrets Solve Magpie Mystery" sidebar] and Taiwan magpies (Urocissa caerulea).
There are other twists too. Mexican jays (Aphelocoma ultramarina) in Arizona may shuttle between several nests maintained by a flock. Flocks of Mexican and Central American brown jays (Psilorhinus morio) maintain only one nest at a time, in which one or several females lay their eggs.
Many corvids, once the young are out of the nest, travel around in small or large, frequently noisy, post-breeding flocks. These groups scour countryside, streets, or forests for food. Winter roosts of crows form from fall until early spring. At these night roosts, up to 50,000 birds may be packed into one acre. Rockville, Maryland's famous fall and winter roost now gathers in trees lining large parking lots along a stretch of Rockville Pike. The dawn and dusk goings and comings of countless crows against a rose sky is perhaps the city's most awesome natural spectacle.
Death and Disease
Nowadays, we look to our crow neighbors to help us gauge
the spread of a much-feared illness. The West Nile virus,
a sickness widespread in the Old World, first reached
U.S. soil in New York in 1999. American crows soon became
important indicators of the mosquito-borne virus because
crow die-offs occurred as the birds were exposed to
the new pathogen. To date, dead crows found as far south
as North Carolina have tested positive for West Nile.
In a paper published in 2000 in the National Center
for Infectious Disease's journal, National Zoo Conservation
& Research Center biologists John H. Rappole and
Scott R. Derrickson and their Czech colleague Zdenek
Hubalek wrote that migratory birds, including crows,
could contribute to the virus's spread, and that longer-distance
migrants such as ducks or gulls may, in the future,
help facilitate outbreaks throughout the Western Hemisphere.
In the East, intensive spraying campaigns, feared by many to be harmful to wildlife and potentially to humans, aim to control the disease's spread by combating mosquitoes in affected areas. Crows are not suspected to have brought the virus, since North American corvids do not migrate across the Atlantic. A trans-Atlantic migrant species (such as a duck called the Eurasian wigeon, Anas penelope) would be more likely, but more likely still would be birds legally or illegally imported into New York.
So far, the disease has killed thousands of birds and eight people. In October 2000, the U.S. Geological Survey (USGS) revealed that lab experiments proved what had been previously feared—that birds can spread the disease among themselves without the presence of a mosquito vector. "We know that crows are highly susceptible to the virus and that they are more likely than other bird species that live in close contact with one another to transmit the disease to other crows," said Robert McLean, director of the USGS National Wildlife Health Center. "We know that the virus attacks the crow's entire body and often affects all the major organs. So far we don't know how sensitive other bird species are to the West Nile virus."
Another introduced pathogen could finish off an endemic crow that lives in the United States' most far-flung state. The Hawaiian crow (Corvus hawaiiensis), or 'Alala, is one of the world's most endangered species. In the past, these forest crows flourished, but they have since declined due to large-scale, human-wrought habitat change, introduced diseases and predators, and shooting. Today, fewer than 30 individuals remain, 26 of which live in a breeding facility on the island of Hawaii. There, an endangered species recovery team that includes the Zoo’s Scott Derrickson puzzles over ways to save the species. Toxoplasmosis, a disease usually fatal to the island crows, has been spread by feral cats, which are difficult to control in Hawaii's lush forests. Meanwhile, the crows' traditional predators, endangered 'Io (Buteo solitarius), or Hawaiian hawks, find the few remaining disease-addled wild crows to be easy targets.
Other corvids lead precarious lives due to habitat destruction in their limited ranges, including the Ceylon magpie (Urocissa ornata), Mexico's dwarf jay (Cyanolyca nana), the Sichuan jay (Perisoreus internigrans), and the white-necked crow (Corvus leucognaphalus) of Haiti and the Dominican Republic. Little is known about most of these threatened birds. In many ways, even the natural histories of the commonest crows remain a bit murky. For example, many would like to know how the expansive breeding range of the gray-and-black hooded crow became sandwiched between that of the species' all-black populations, called the carrion crow (Corvus corone corone). Many experts believe that the last ice ages cleaved and isolated the black crow populations, and that mutation produced the hooded population in one of the enclaves. Then, after glaciation, the once-separated populations merged. Russian biologist Alexei Kryukov has toiled over this issue for years, and studied these birds at one of their hybridization zones in Siberia. "According to my recent molecular data, both forms—black and gray—are very similar," he says. "I speculated that their origin was in East Asia, and that the black spread to Western Europe, then divided to three forms [two black and one gray and black], which formed two hybrid zones recently."
Recent findings paint a somewhat similar picture for California's ravens. A December 2000 USGS press release declares that "ravens from Minnesota, Maine, and Alaska are more similar to ravens from Asia and Europe than they are to ravens from California." The reason: genetic testing yielded dramatic differences between the populations, suggesting that California's ravens might have become marooned from other raven populations perhaps two million years ago. Similarly, the American West's black-billed magpie is now considered by many experts to be the American magpie (Pica hudsonia) because it exhibits more genetic similarities to California's yellow-billed magpie (P. nuttalli) than the widespread magpie (P. pica) of Eurasia, with which it once shared species status.
Other mysteries relating to common corvid distribution await resolution. Many birders and scientists, for example, puzzle over the coexistence of two eastern North American crows that are virtually indistinguishable in the field when silent. Some experts theorize that fish crows (Corvus ossifragus) form a "superspecies" with two Mexican crow species and are not as closely related to American crows as they might appear. The two species can only be identified in the field by their different calls—“caw" in American crow and "cu-uh" in fish crow. However, even this identification tool is not 100-percent sure. Members of both species feed and breed at the Zoo and in Rock Creek Park; they winter together in huge roosts.
As human cities and suburbs grow, so do populations of many of the world's scrappy corvids. As any successful businessperson will tell you, when it comes to survival, flexibility is key. You must adapt to the market, and find your niche. So it goes with both corporate or corvid survival. While many still disdain the sight of crows, few can deny that their widespread presence is testimony to their success, and ours.
—Contributing editor Howard Youth currently lives in downtown Madrid, where magpies expertly navigate rooftop forests of television antennae.
ZooGoer 30(3) 2001. Copyright 2001 Friends of the National Zoo. All rights reserved.
