THE SECRET LIVES OF CROWSCrows. They're often portrayed in literature and movies as harbingers of doom (who can forget the Black Menace in the movie Bill and Coo?) or as crafty pests (the heckling crow flock in Dumbo). We like them because they are curious and cheeky; we dislike them because they're loud and annoying. In our minds, we all think we can characterize and pigeonhole crows as we assign them a lot of humanlike attributes. But through a decade of research, crow expert Kevin McGowan has found that we don't know as much as we think we know, and through the fascinating process of trying to unravel and interpret crow behavior he has opened up a whole new set of questions.
"We basically don't know anything about these birds," says McGowan from his office at Cornell's Vertebrate Collections, where he serves as curator of the ornithology and mammalogy collections. Outside, the late afternoon winter sun is starting to set, and as McGowan gets up from his desk to fetch me a copy of some data, he pauses at his window and looks through a spotting scope trained on some distant trees. He can't help himself.
Although the American Crow is one of the best-known and most common birds in North America, only a handful of researchers are studying the species. "When I started looking at American Crows in the late 1980s," says McGowan, "the most cited source was an unpublished Ph.D. thesis from the 1950s about crows in rural Ohio." Ten years later, there is still a dearth of material about these birds.
"They"re hard to keep track of," he says. "Initially, I wanted to test questions about cooperative breeding, but I had trouble following the adults--they fly too far and are too wary." And catching adult crows is difficult at best. The birds are intelligent and suspicious. Though some Australian researchers have devised a trap specifically for crows, it's big, tricky to operate, and not very portable. McGowan thinks that a cannon net might be effective--but only once in any particular area before the birds catch on and stay away--and it couldn't be used in a city, where it would probably come under the same laws that govern discharging firearms.
So McGowan decided to study the basic nesting biology of American Crows. This involves banding and placing wing-tags on nestlings in hopes of later recording and studying the movements of the birds as they grow up and disperse. Although McGowan usually has field assistants, this time-consuming process--it takes up to half an hour to band and tag each bird--sets limits on the size of his research sample. He can only process four or five nests a day. Additionally, he has only a very narrow window of time in which to tag the birds--when the nestlings have nearly full-grown feathers but can't yet fly--which further limits the sample size. "There are just so many hours of daylight in the day," McGowan laments.
|The typical crow's nest is a well-built structure of sticks and twigs woven tightly together and lined with grasses. A number of the nests McGowan studies are located in urban settings (above). Comparing urban nests with rural nests, McGowan found that the city crows produce one fewer young than the country crows and their offspring are significantly smaller. At right, a clutch of crow eggs.|
Kevin McGowan grew up in Ohio, receiving bachelor of science and master of science degrees in zoology from Ohio State University and a Ph.D. in biology from the University of South Florida for his work on the social development of young Florida Scrub-Jays. He came to Cornell University in 1988 as a curatorial and research associate in the Section of Ecology and Systematics. In 1994, he was promoted to senior research associate and is the principle caretaker of Cornell's bird and mammal collections.
McGowan became interested in crows while he was still in Florida, but when he moved to Ithaca he knew he had hit crow heaven. Through a small grant from the United States Department of Agriculture he began his decade-long study of crows, which have historically been regarded as agricultural pests. One of McGowan's findings is that although crows can be local crop pests--which can be more than a nuisance to individual farmers--they have a very minimal impact on overall agricultural devastation, which dispels a popular misconception.
As he began studying crows (primarily American Crows, though he has also been following a small population of Fish Crows in Ithaca), all sorts of questions started to emerge. Are crows territorial? What constitutes a crow family? What is each bird's role in the family group? Do differences exist between rural and urban crows?
McGowan has tagged 651 individual crows from 560 nests over the past 10 years. And he has made some basic discoveries. First, American Crows are cooperative breeders. They apparently mate for life, or until a mate becomes incapacitated, and often several generations of a single family can be found helping at a nest. Older siblings, known as helpers, may take part in building the nest, feeding the incubating female, feeding the hatchlings, and chasing away predators. "Some of these families are amazing," says McGowan. "One marvelously successful crow family lives at St. Catherine's Church in Ithaca--a breeding pair and up to seven generations of siblings live on or next to the home territory there."
According to McGowan, each breeding pair has an established home territory (averaging about 10 acres in the city and much larger in the country), where they build their nests and raise young. And they hold these territories throughout the year. Nonbreeders or helpers associated with the territory may leave for a while in the winter, but many of them eventually return to their parents and their home territories. Young crows wait at least two or more years before breeding, so family groups can grow quite large--the family at St. Catherine's Church has up to 15 individuals--and it's not unusual to have three or more adults attending a single nest. This can make the demographics of the home territory pretty complicated.
Crows have several ways to become breeders: they can leave home; they can wait for another crow in the neighborhood to die and then take its territory; they can take over a portion of their parents' territory; or they can essentially inherit their parents' territory when they die. McGowan found that American Crow family groups are dominated by males--male offspring tend to stay close to home whereas their sisters disperse.
McGowan's research area includes the City of Ithaca and its surrounding suburbs, then north to the Tompkins County Airport and east to Willow Glen cemetery outside of Dryden, a village about eight miles from Ithaca. He tracks between 50 and 75 nests each year, and between 45 and 75 percent of them successfully produce young. "I tend to keep track of the crow families I've followed the longest,Ó says McGowan, but he also adds new families each year to expand his research pool. Each nest produces on average four-and-one-half eggs annually, from which three birds usually fledge. Great Horned Owls, Red-tailed Hawks, raccoons, and even squirrels prey on crow eggs and nestlings, so crow parents go to great lengths to conceal and then protect their nests.
"Nests are not homes," stresses McGowan. "They're just temporary structures that serve a purpose." It behooves the young birds to get out of the nest as quickly as possible, so that they will be less vulnerable to nest predators. Compared to the nest-success rate of birds that build small open-cup nests (only one-third of their young fledge), the nest-success rate of American Crows is high. Crows rebuild their nests every year, so in March, when McGowan starts looking for crow nests, he knows that a nest won't be in the same location as it was the previous year, but that it will be somewhere on the family's territory.
From late summer until the following spring, a lot more activity takes place away from the territory because the need to feed and defend the young is gone. Some crows migrate to Ithaca from northern Canada and join the nonbreeding flocks that spend their days foraging around the countryside. But toward dusk, you'll notice all of a sudden that no crows are around--they've all gone to congregation areas to prepare for the night's roost. "There's a lot of talking back and forth and playing around at these preroosting sites," says McGowan. Then as it gets dark, they take off and head into the trees and their roost. Even the breeders sleep in the roost and leave early in the morning to head back to their territories. McGowan found a roost in Cayuga Heights, a suburb of Ithaca, that had about 1,200 birds in it, which is actually not that large compared to some. Apparently a roost at the state penitentiary in Auburn, New York, numbers between 25,000 and 40,000 crows. And these are big, noisy birds.
|Each young crow in McGowan's study nests is banded and also equipped with a lettered and colored tag on each wing (above). The letters are unique for each individual, and the color indicates the year of its birth. At right, McGowan poses with a newly tagged young crow just before returning it to its nest.|
A couple of winters ago, McGowan censused the large flock of crows that congregated at Cornell University's Game Farm each day to feed on the constant food source of manure and corn. He wondered which crows these were and where they came from. The birds were coming and going constantly. He censused the flock 32 times, and of the approximately 200 individuals that were there at any one time, he counted and identified 67 tagged crows. But half of them were there only once. "It's just like going to the mall," he said. "Although it's packed with people every day, the individuals change." Ithaca and its suburbs have about 200 crow territories, but in the rural parts of the county, the nests probably number in the thousands. McGowan began wondering whether any differences exist between urban and rural crows, so he started tracking 10 to 20 rural crow families each year. "Crows didn't move into towns and cities until the late 1950s," says McGowan. And although crows are opportunistic, he was curious about how well they were adapting to city life. What he found surprised him. "The urban nests are marginally, though not significantly, more likely to succeed," says McGowan. "But the rural crows produce one more young per successful nest and the nestlings are substantially larger--50 grams larger--than urban nestlings."
This finding surprised McGowan. After all, the city birds have a constant food source with the weekly trash pickups. Then he found part of his answer. Several years ago a drought hit the area--it was among the top 10 driest winters on record and one of the driest springs ever--and, according to McGowan, the urban crows fared poorly. That led him to realize how dependent even the urban crows are on one particular food source: earthworms, which were extremely scarce and rarely came to the surface during the drought.
McGowan also suspects that city territories are too small and that urban crows are not getting reliable cues about how large a territory needs to be to ensure survival. But to McGowan this just illustrates how little we know about the rules crows follow about territories--for example, how are they established, who stays, and who leaves?
As I write this article, it is still winter in Ithaca. Six inches of snow blanket the ground, and the temperature is hovering in the low thirties. Now, of course, everywhere I look I see crows. I search each flock for "Kevin's crows"--ones with square plastic wing tags marked with large block letters to identify the family group and individual and different colors for each generation. I tell him I don't see many tagged crows around. McGowan laughs. "Remember, my crows disperse into a population of 125,000 crows," he says, "and I've only tagged 651 of them."
A VISIT WITH SOME CORNELL CROWS
It is a warm morning in early May, and
we are congregated in the parking lot above Cornell University's Synchrotron lab.
Kevin McGowan is here, along with two student assistants, Living Bird editor Tim
Gallagher, and myself. Quickly donning hardhats, we follow McGowan to the
nest site--a tall, straight pine tree at the edge of a picturesque gorge. Below us,
Fall Creek flows swiftly past, roaring as it crashes over a waterfall a few hundred feet
--Rachel J. Dickinson
Rachel J. Dickinson is a freelance writer based in Freeville, New York. Her articles frequently appear in this magazine.
| BACK | BECOME A LAB MEMBER | LAB SPONSORS | FEEDBACK |