We've all seen them: big, black, sometimes noisy birds that hang out on telephone wires and fence posts and in trees. They're amazing aerialists, flying loop-the-loops around other birds. We may like them because they're curious and cheeky. We may dislike them because they're loud and annoying.
Through studying these birds, crow expert Kevin McGowan has found that we don't know very much about crows. It turns out they are smarter and more complicated than we imagined.
"We basically don't know anything about these birds," says Dr. McGowan from his office at Cornell University in Ithaca, N.Y. McGowan studies crows by attaching numbered leg bands and wing tags to the nestling crows so he can track them (at least until the wing tags fall off, which they do). Often he works alone, and it's a time-consuming process. It may take 30 minutes to band and tag a single bird.
What makes up a crow family? What is each bird's role in the family? Are crows territorial? That is, do they claim a particular area as their own and keep other crows out? Are there differences between city crows and country crows?
McGowan has found that crows are "cooperative breeders." In other words, several adult birds participate in hatching and rearing baby crows. Also, crows mate for life, essentially, and crow families tend to stick together. McGowan has seen up to seven generations of a crow family in one spot.
Older siblings may help build the nest, feed the parent bird sitting on the eggs, feed the hatchlings, or chase away predators such as great horned owls and red-tailed hawks.
Each breeding pair of crows has an established home territory where they build nests and raise their young. Urban territories are about 10 acres, but rural territories are much larger. Crows hold their territories year-round.
Non-breeding crows may leave the family territory for a while in the winter, but many return to their parents in the spring. Young crows don't leave to breed for two or more years, so family groups on the home territory can grow large. One crow family in Ithaca has up to 15 members. And it's not unusual to have three or more adults attending a single nest.
This can make it difficult to figure out who's who in the home territory.
McGowan tracks between 50 and 75 nests each year. One-half to three-quarters of the nests produce offspring.
"I tend to keep track of the families I've followed the longest," McGowan says. He adds new families to expand his research pool. The average number of fledglings (birds old enough to fly) per nest is three.
Owls, hawks, raccoons, and even squirrels pose a danger to eggs and young birds, so crow parents go to great lengths to conceal and protect their nests.
"Nests are not homes," McGowan stresses. "They are just temporary structures that serve a purpose." Crows rebuild their nests every year, so when McGowan starts looking for crow nests - big, messy stick structures - all he knows is that a crow won't be nesting where it nested the year before. The new nest will be somewhere in the family's territory, though.
On late afternoons in the fall and winter, you may have suddenly noticed there were no crows around. Where did they go? They all got together in areas to prepare for the night's roost. The congregated crows talk and play at these places until dusk. Then they fly to their communal roost, usually in tall trees, where they spend the night. These roosts often hold several hundred birds and sometimes up to a million of the big (17 to 21 inches long), noisy creatures.
'Crow busters' in Harrisburg
A roost of about 50,000 birds is located outside the Auburn Penitentiary in Auburn, N.Y. Lloyd Fales co-produced a television show on crow roosts for National Geographic Explorer (it airs June 2 at 8 p.m. on TBS; check local listings). He visited the Auburn roost last winter. The clamor is incredibly loud when the crows first fly in, he says. The city is still divided on the issue of the crow roost: Should they try to get rid of it or take steps to preserve it? Mr. Fales has found, through his research, that it is very difficult to discourage crows from roosting in a spot they've chosen.
Harrisburg, Pa., "had a crow roost of between 10,000 and 20,000 birds right in the capital complex," Fales says. "The city had to call in professional crow-dispersal people from the United States Department of Agriculture to deal with it." The dispersal team shot off fireworks (cracker shells and "bird bombs") every night while a truck with a sound system blared a tape of crow distress calls.
"For a couple of weeks it was like a war zone," Fales says, "but they did manage to relocate the roost to another part of the city."
Why would crows choose to roost in a city in the first place? No one knows for sure. But city parks and cemeteries have some of the biggest trees around, and crows like big, tall trees for their roosts. Crows also like to congregate near lights because their night vision is poor. Bright lights give them a better chance to elude predators.
McGowan thinks that crows exchange information at their roosts. If a crow hasn't found much to eat one day, for example, it might watch for fellow crows that look well-fed. Then the hungry crow follows his fatter friends to their feeding area in the morning. The social interaction that occurs at roosts may also be a way crows establish the pecking order of their society.
Mystery of the city crows
Are country crows different from city crows? McGowan notes that crows didn't start moving into towns and cities until the late 1950s. He was interested to see how crows have adapted to city life.
What he found surprised him. Nests in urban areas were slightly more successful in producing offspring, but the offspring were a lot smaller. City-bred nestlings weighed 50 grams (1.75 ounces) less than their rural relations' offspring did.
This was surprising. After all, there seems to be a lot more food for crows in cities, what with weekly trash pickups and dumpsters. Why weren't the city crows bigger? Then McGowan found part of the answer: drought.
Ithaca had experienced a drought several years ago. It was one of the 10 driest winters on record and the driest spring ever. According to McGowan, "the urban guys did terribly." That made McGowan realize how dependent even urban crows are on a particular food source - earthworms. Dry earth meant fewer worms, and smaller crows.
McGowan also suspects that city territories are just too small because urban crows have not figured out how large a territory needs to be to ensure survival.
The move into towns and cities happened around the world with other corvids (crows, jays, magpies, ravens, and others). Was it a change in human behavior that made cities more hospitable to crows? In America it became illegal to discharge firearms in urban areas around the 1950s. Did this help birds overcome their fear of humans? We don't know. But we do know that crows -along with coyotes and foxes - are adapting to city life, giving us all an opportunity to coexist with nature.