It seemed like the crow could recognize Marzluff’s face, but of course it could have been something else: his scent, the curve of his shoulders, the particular cadence of his walk. So Marzluff bought a Halloween mask of a bald and bucktoothed caveman with a massive ledge of forehead hanging over the eyes and had his students wear it while capturing birds at the University of Washington. Sure enough, after that, whenever anyone wore the mask the crows would go crazy. Just to make sure they hadn’t accidentally discovered that crows simply hate disguises, Marzluff got an even more terrifying mask—one that looked like former vice president Dick Cheney—and walked around campus with it on. The crows had no quarrel with Cheney, but continued to harass anyone who wore the caveman mask.
It was a tremendous feat to prove that crows recognize human faces, but what happened next was, to my mind, even more extraordinary. More and more crows flocked to scold the caveman, and some of these crows had no leg bands. “Not only was the crows’ hatred of the caveman persistent,” Marzluff wrote, “it was getting worse with time. . . . The number of birds scolding the caveman on a typical walk has increased threefold. And the vast majority of those who berate the Neanderthal were never even touched by him.”
Crows were teaching each other to fear this bogeyman. This has been going on for eight years, and there’s no sign they will forget the grudge. People who learn about this research are often captivated by the masks and fixate on the fact that crows can recognize individual people, Marzluff says. But the ability to see and remember visual markers in a face is a relatively simple cognitive task. Wasps, for instance, have it down pat: They identify one another by their facial markings. Dogs, monkeys, and pigeons can also recognize individual humans; so can sheep, honeybees, and even octopuses.
I think it seems strange to us because crows are doing something that we can’t: differentiating the members of the other species. Most people can’t differentiate individual crows. It’s actually more correct to say that we don’t recognize individual crows, instead of saying that we can’t. Our face blindness is self-imposed, because we could see the differences between crows if we actually looked. After all, pet owners quickly learn to recognize their pets even when they’re with others of the same breed.
To focus entirely on crows recognizing faces is to miss the most astonishing thing that Marzluff discovered: Fledglings learned to fear the caveman in the abstract. The young birds never actually saw the masked man capturing other crows, they had only seen their parents scold him. One generation passed the information to the next: This momentous thing happened to our kind. Learn it. Never forget it. Teach your children. This transmission of information is challenging enough that only the most intelligent creatures can manage it. It allows for the formation of tradition. In fact, it seems to me that if you take the same phenomenon and perpetuate it for thousands of years, you have something that looks very much like a religious observance. What are seders or the rituals of Christmas but means of perpetuating deep cultural memories? Perhaps those crows I saw mobbing red-tailed hawks were not showing off or playing, but instead reenacting an ancient ceremony so laden with meaning that I could not hope to understand it with simple evolutionary explanations.
Love, Hate, and Obsession
There’s a clear evolutionary advantage in being able to differentiate one person from another when one of them will try to shoot you and the other will feed you peanuts. Crows use their facial recognition ability to torment those who cross them, and also to reward those who help them. They sometimes leave little gifts for friends. Angell and Marzluff report that on Valentine’s Day of 2006, nature writer Gary Clark jokingly asked the crows he regularly fed why they never brought him anything in return. Later that day, when he returned to retrieve his feeding tray, he found a candy heart placed exactly in the center with LOVE printed on one side. Surely the timing of this gift—and the message it bore—was coincidental (no scientists think crows can read), but lots of people have received gifts from crows after feeding them.
Those who anger crows, on the other hand, suffer creative retribution. Carolee Caffrey, a zoologist at Oklahoma State, has described a crow expertly bombarding a student with pine-cones. The student was climbing a tree to study the crow’s nest, and the crow plucked three pinecones and dropped each on the student’s head.
In another story collected by Angell and Marzluff, Seattle resident Gene Carter earned the ire of his neighborhood crows by scaring them away from a robin’s nest. After that, a crow scolded him every morning and evening when it spotted him walking to and from his bus stop. The bird would dive toward him threateningly, “occasionally rapping him on the head, always amusing his wife and fellow commuters,” they write. This went on for a year, until Gene moved to a new house. He was careful to move each load of his belongings to the new residence by a circuitous route to avoid being followed, immediately giving up and turning back if he saw a crow.
WHAT MAKES A CROW
I found that crows are a bit more difficult to observe carefully than some of the other species I’d begun to watch in writing this book. Crows are liable to fly off: They’re not wedded to any one spot. And they are aware, and suspicious, of observers. When I watch them, they watch me. I don’t need to take a single step toward a group of crows to arouse their vigilance, it’s enough just to stop and stare at them instead of continuing with the flow of foot traffic. Pigeons are glad for human company and seek our patronage. Easily distracted squirrels quickly forget that you are there. To ants, we are incomprehensibly foreign. And to ginkgos our lives are insubstantial shadows, flitting past. But to crows, we are peers. They know better than to trust us, and unless there’s good reason to share, they keep their secrets to themselves.
One soggy Sunday afternoon as Josephine and I walked to the grocery store, Josephine pointed out a pair of black shapes on a rooftop, their profiles sharp against the iron-gray sky. The crows were dipping their beaks into the roof’s gutter and plucking something out, but it was impossible to see what it was with the naked eye.
They went about their work with the busy economy of motion of farmworkers harvesting a row of crops—though these farmworkers stopped every few seconds to watch the large carnivorous creatures who stood watching them. One crow fluttered to the next roof over and began working its gutter. I speculated aloud that there might be fat grubs living in the gutter leaf litter. Josephine suggested it was more likely that the crows were eating chocolates. Later, Swift would tell me that Josephine’s guess might have been closer. She often uses Cheetos to gain crows’ trust, and they love to hide these treats—and other food—in gutters.
The crows pecked busily. Then they flew away: darker wings against dark clouds.
The Blackness of Crows
The blackness of crows fairly radiates from their feathers, which impressed itself upon me when I took my lunch to a park one day. I found a seat near a pair of crows perched in a tree. One of the birds had a white streak on the underside of one of its tail feathers. I thought at first that this was a guano stain, but it didn’t look like it: It was very pure white, not clumpy or streaked. When I checked into it later, I learned that many birds do indeed lack pigment in a few feathers.
I watched my white-streaked crow (and it watched me back) while I ate a quesadilla and wondered, Why black?
Lyanda Lynn Haupt, in her book Crow Planet, described crow colors in detail after she spent two full days staring at one on her desk (a stuffed scientific specimen) to see if she could open her eyes to something new. She noticed that the innermost half of breast feathers—the part usually covered by other feathers—was gray and explained, “It takes some biological effort to produce dark pigmentation, and if it is not needed because the feathers are not visible, then natural selection does away with it.”
Basic pigmentation must be pretty cheap (biologically speaking), or else creatures without coloring or patterns would be everywhere. But I could imagine that producing that deep, silky blackness does demand more resou
rces than gray does. You can glimpse the gray when the wind disturbs the breast of a crow.
If blackness is biologically expensive, what are crows (and blackbirds, and ravens) getting in return for paying this premium? Nobody knows for sure, but there seems to be a provisional consensus among ornithologists that the blackness allows the birds to be seen.
Many animals are patterned for camouflage: Any variation in color helps break up the profile of the creature. If a tiger is creeping up on me through the jungle, for instance, instead of seeing a solid block of orange in the shape of a tiger, I’ll see stripes of orange and black, which would be easy to misinterpret as branches, shadows, and shafts of light. Pure black, on the other hand, stands out against almost all of nature’s backgrounds. There’s no misinterpreting the shape when it’s all one color. This visibility is helpful for social birds like crows because it allows members of a group to see each other clearly. An individual crow is puny, but a murder of crows can chase off eagles—and drive grown men to change their addresses.
Even an all-black dress code can contain further complexities. After staring at her crow for hours, Haupt noticed that “the black glossy feathers on the crown and back are outlined with iridescent violet, giving them a scaled appearance.” This contrasts with the feathers on the back of the neck, which are flat black. The small body feathers, Haupt wrote, are “as soft as rabbit fur,” while the wing and tail feathers are stiff.
Ravens and Crows
Here is how I try to tell if I’m looking at a raven or a crow. If the bird is flying, I look at the tail. Crows have a rounded fan. Ravens have a diamond-shaped tail. I also watch the bird closely when it lands. Ravens are quiet and still. Crows fidget and complain. Their voices are different, too. Crows “caw” abrasively. Ravens “rawk” in the pebbled baritone of a woman who has tended a smoky bar for thirty years.
Once I have a pretty good idea, I look for other features to confirm. Ravens are bigger, and they have thicker beaks and a luxurious beard of feathers on the neck. Crows are slimmer: gracile, sleek. The average raven is two and a half pounds to the crow’s one pound, but it’s hard to judge that unless you have the two side by side. Really, though, I identify crows mostly by knowing that ravens are rarer in my neighborhood, so any big black bird I see is probably a crow.
Ravens live just about everywhere on Earth, from deserts to the soggy northwestern coast of America. Crows are a little more particular: They like to be near people. In fact the Asian house crow seems to live only in the company of humans. You could call them obligate synanthropes: They depend on us for their habitat.
Crows do well in the landscapes we create. They like farms, from which they pilfer grain. They like lawns, where they find worms and crane flies. They like bird feeders and bags of garbage and roadkill. Humans supply it all.
CORVID BOOM
One winter, the online news organ in my town, Berkeleyside.com, ran an article on the local multiplication of crows. People had noticed, with some alarm, that every year there were more of them. When the Audubon Society conducted its annual bird counts in the 1980s, there were always fewer than a hundred crows tallied, and just a handful of ravens. After 2010, the birders were regularly counting more than a thousand crows, and as many as three hundred ravens. There are reports that the same is true in other cities.
I hadn’t lived in the area long enough to witness the increase myself, but I had noticed the crows out in force. When I run in the park every morning, there are always small groups of black figures patrolling the grass. Every once in a while I’ll follow a bird’s line of flight to a tree harboring dozens of crows.
People were worried that the crows must have come at the expense of biodiversity. Crows sometimes rob the nests of other birds to eat the eggs and chicks. Would the increase in crows lead to a crash in songbird populations?
Kevin McGowan, a corvid researcher at the Cornell Laboratory of Ornithology, said that wasn’t likely. When researchers put cameras on nests to catch robbers, they found that the culprits usually weren’t crows, they were squirrels or snakes. Crows, McGowan told Berkeleyside, “are way down on the list,” behind raccoons, raptors, opossums, and jays.
Eventually, if the population of crows grows large enough, it can affect the system, Marzluff told me. But the birds that feel the impact also thrive around humans, like robins and jays. The threat to biodiversity comes not from crows, but from humans making drastic changes to habitats. Furthermore, people have tried getting rid of crows, and scientists have watched to see if it helps other birds. To put the findings simply: It just doesn’t work.
I suspect that the dismay accompanying the rising number of crows stems from the sense that every addition to the natural world results in some equal and opposite subtraction. Crows are humanlike in their creativity and their ability to thrive in the ecosystems we shape, so their presence looks to some observers like an extension of human disruption. We lay waste to the earth, and then crows take advantage of the changes and elbow their way in. From this perspective, the booming crow populations look like diminishments of nature.
The evidence, however, doesn’t support this fear. In 2012, ornithologists at UC Berkeley dug up dusty bird surveys dating back to 1913 and compared what they reported with the species they saw on campus. They expected to see a decline, a steady fall from Eden, because so many buildings had gone up on campus, the surrounding area had changed from farms and pastures to an urban grid. But instead, the researchers found a small increase in bird diversity over the century.
Across North America, crow populations are increasing, though much more modestly than by the full order of magnitude seen in Berkeley and other cities. Meanwhile, overall bird diversity has stayed steady. In the United States, the Environmental Protection Agency found that 113 bird species have suffered significant declines in the last half century. But at the same time, 118 species have benefited from significant increases in numbers.
City Birds
There’s one more question embedded in the observation that crow populations are increasing. That question is: Why are the biggest increases in cities?
The answers are slightly different across America. The American crow isn’t endemic to the West Coast, it followed suburban developments across the United States, glorying in the irrigated lawns that turned the inhospitable West into ideal habitat. They reached the West Coast sometime around 1960, Marzluff said. Part of their increase in western cities is attributable to their colonization of new land.
In eastern North America the most likely explanation for booming urban crow populations is that they are moving from the countryside into towns. And we know with certainty that this is happening. By doing a little historical research, McGowan found that at least one roost had moved from three miles outside the town of Auburn, New York, in the 1930s to the middle of town. And many other cities—Pittsburgh, Albuquerque, Minneapolis, and Ottawa, Canada—have seen roosts develop.
A roost is a great congress of birds gathered for the night. Starlings and nuthatches also roost, as do robins, though in lesser numbers. Crows often roost together through the winter, then separate in the spring to build nests for eggs. These roosts can grow stupendously large. One, in Fort Cobb, Oklahoma, had around two million crows. McGowan describes standing beneath a roost of more than fifteen thousand crows in central Ohio and marveling at the volume of excrement underfoot. Crows, like many birds, swallow bits of rock to help break down the grain they eat, and McGowan estimated that the crows in that particular roost could drop 1,650 pounds of gravel around that tree every five months.
If there are more roosts moving into cities, then it stands to reason that crows are staying in towns during the day as well. But why have they moved?
Maybe it’s because there are laws against firing guns within most cities. Now that we are no longer primarily agrarian and scarecrows are a symbol rather than a practical tool, we don’t see crows as our enemies. And vice versa: Crows may have simply gotten more comfortable bei
ng surrounded by humans all the time. Marzluff notes that city crows tend to be much less skittish around people, and more likely to aggressively scold humans.
McGowan suggests that the move to cities might also have something to do with the invention of streetlights. Great horned owls are the most effective predator of crows, swooping in noiselessly from the dark to grab them. But few owls penetrate to the city centers, and with the glow from the streetlights, the crows have a chance to see them coming. (Crows, like most birds, can’t see very well in the dark.)
McGowan also says that crows are roosting in cities because that’s where the trees are. The grand old trees in parks and cemeteries are often the largest trees around, the only ones to survive the most intense period of logging and development. Since the early 1900s, urban forests have sprung up. If you look at pictures of American cities from a century ago, you’ll find many streets were treeless. By foresting along the sidewalks, we’ve created a habitat that simply didn’t exist before, a massive surface area composed of branches for nesting and perching. The leaves and berries, the insects that feed off them, and the spiders that eat those insects are all in turn the food for birds and other creatures.
I find all this tremendously heartening. Instead of being a symptom of human destruction, crows seem to be moving in because, at least for them, we are improving the habitat. In his book Welcome to Subirdia, Marzluff tells how he spent two weeks birding in Montana’s Glacier National Park, then flew to New York and went out bird-watching in Central Park. He was surprised to discover that in New York, he saw a greater diversity of birds by midday than he had during his entire stay in Glacier National Park. The science supports his experience. Studies have found there is very low diversity in bird species at the concrete core of a city when there are no nearby parks. The biodiversity of remote woodlands is higher than that. But the greatest number of unique bird species can be found in cities that have big parks.
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