Feral Cities

by Tristan Donovan

  Regardless of species, most stick to the older neighborhoods. “Where we have the largest numbers of parrots, perhaps not coincidentally, are in areas that used to be orchards of fruit trees and nut trees, many of which were retained when the area was urbanized,” says Kimball.

  Like the monk parakeets of Brooklyn, L.A.’s parrots have their own unproven, and unprovable, origin stories. One theory is that many found their freedom in the Bel Air fire of November 1961. The fire destroyed hundreds of homes and forced thousands to flee for their safety. It is thought that in the rush to escape the blaze, parrot owners freed their birds en masse so they would not be burned alive in their cages. Soon after, people began reporting sightings of green parrots all over the city.

  Another story concerns the bird sanctuary that Anheuser-Busch used to run in Van Nuys. The sanctuary held more than fifteen hundred birds, including many parrots, but at the end of the 1970s the beer maker shut it down so it could expand its brewing facilities. It is thought that some of the parrots may have escaped as they were being transferred to new owners, possibly by using their powerful beaks to pull apart the bars on their cages before flying to freedom.

  Yet despite decades of living wild in the streets of L.A., there’s little sign that the birds want to follow the example of the European starling and go beyond the city limits. “A great many of them seem to thrive in highly modified suburban and urban habitat as opposed to natural habitats,” says Kimball. “They can move out of cities into more sparsely populated areas but, by and large, this doesn’t happen.”

  Access to exotic plants seems to be what keeps them in the city. “The parrots are dependent on a mix of particular food plants that are really only planted where people live, so they are not going to find food in natural areas.” These plants include the silk floss tree. “The yellow-chevroned parakeet uses the seed pods from the silk floss tree and encounters the same tree within its native range in South America, so we’ve kind of reunited them here,” says Kimball.

  The much-maligned eucalyptus is another favorite. “Ecologists all say eucalyptus are horrible and don’t belong here, but they are a magnet for birds. There’s a eucalyptus just outside the entrance to the Natural History Museum that’s infested with sap-sucking lerp psyllids that create these honeydew combs on the leaves that are candy for birds. For birds, it’s the best tree in the whole park.”

  Our taste for exotic vegetation may allow parrots to thrive in cities, but they are mere amateurs compared with the pigeon.

  The rock pigeon is very much the defining bird of the urban landscape, a daily sight in cities the world over from Los Angeles and London to Dubai and Sydney. But unlike the colorful and amusing parrots, the pigeon is rarely loved. We dismiss them as ugly pests, deriding them as little more than “rats with wings.” They are birds that peck at the dirt, annoy us with their burbling coos, and stain the sidewalks—and sometimes us too—with their excrement.

  We only have ourselves to blame, though, for the city pigeon is our fault, a genetically modified creature born out of our own desires. The street pigeon’s ancestors may have been unremarkable cliff-dwelling birds, but for thousands of years we have been molding them for our own ends, turning them bit by bit into birds ideally suited to the city. Like the house sparrow, pigeons began living beside us in the formative years of human civilization, making homes in the holes of the mud and stone homes we built.

  People didn’t mind. After all, what could be more convenient than having one on your doorstep when you fancied eating pigeon? There were other benefits too. Their nitrogen-rich guano made a great fertilizer as well as proving useful when tanning leather.

  Another boon was their impressive homing abilities. We still don’t fully understand how they do it, but it seems to depend on a combination of detecting magnetic fields, visual recognition of landmarks, understanding the sun’s movements, and smell. While we don’t know how pigeons do it, we have been using their homing capabilities for thousands of years; they even spread the news of Ramses III’s coronation as pharaoh of Ancient Egypt.

  Keen to exploit these useful birds, people began building nest houses called dovecotes to attract them. For the pigeons, it was a good deal. They got protection from predators and bad weather, plus easy access to our farms and the grain and seed that were spilled on the streets. The only downside was the risk of being grabbed if someone opted for a pigeon dinner. But it was worth the risk.

  The dovecote spread across the world. The Romans took the idea from Egypt and spread it across Europe. The Spanish and Portuguese took them to South America, and the British and French introduced them to North America.

  People also began domesticating the birds, encouraging the breeding of those with useful traits like speed, homing ability, fertility, beauty, and tameness. Over time we molded the former cliff dwellers into something almost new, weeding out the undesirable genes and multiplying the beneficial in much the same way we turned gray wolves into domestic dogs and fostered more productive cattle.

  But not every pigeon played along. Some rebelled, abandoning the dovecotes to make their own way on the streets, where the characteristics we bred into them turned out to be powerful assets. Their tameness made them unfazed by crowds of people, enabling them to forage in the busiest parts of our cities, such as London’s Waterloo railway station through which a quarter of million passengers pass every day.

  Pigeons’ speed and agility helped them dodge traffic and escape predators, which they sometimes evade by diving off buildings and using gravity to accelerate to speeds as high as thirty-seven miles per hour before making their escape. Even peregrine falcons can find pigeons hard to catch, thanks to their habit of giving them the slip by zig-zagging through trees and buildings.

  Our desire for fast-breeding domestic pigeons gave them the ability to breed year-round, so that a single pair of feral pigeons can produce as many as ten squabs a year. Pigeons also proved themselves to be adaptable birds, making nests out of twigs, paper, and metal wire in locations as unlikely as satellite dishes and neon signs.

  They also learn from each other. In Montreal, Canada, researchers caught feral pigeons and taught them how to open paper food containers by using their beaks to pierce and then widen holes. After teaching the birds how to do this, they returned them to streets. Soon the container opening technique began to spread among the pigeons of Montreal, as other pigeons copied the ways of those trained by the researchers.

  Contrary to their image, pigeons are also not as dependent on garbage as we imagine, and their reliance on what we throw away depends on where they live. In the English city of Leeds, half of what pigeons eat consists of garbage and food provided by people on bird tables or in feeders, but in the Czech capital Prague, human food is a mere 3 percent of their diet.

  In fact many pigeons don’t even eat in the streets of the cities they live in. Take the Italian city of Milan. On the face of it, it seems like the kind of place where pigeons would look to the streets for food. In the Piazza del Duomo, home to the city’s grand cathedral, pigeons gather by the thousands to gobble feed dished out by tourists and pigeon-friendly locals. Yet half of Milan’s hundred-thousand-odd pigeons don’t eat on the streets. Instead they wake each morning and fly out to the farms surrounding Milan, where they spend the day feeding on grain before returning back to their city nests in the late afternoon.

  While pigeons had our help in becoming the world’s most abundant urban bird, others have to rely on their wits, and when it comes to brainpower few birds can match the corvids. The corvid family of birds, which includes crows, ravens and magpies, has the brainiest birds around, clever enough to rival apes and dolphins in the intelligence stakes. And their cleverness has helped them turn the city to their advantage, even if they can’t pump out eggs anywhere near as fast as feral pigeons.

  The jungle crows of Tokyo, which have relatively long beaks and dark gray plumage, are a prime example. They’ve figured out ingenious ways for stealing food from th
e bowls of dogs kept in backyards. Some crows land on dog kennels and drop objects onto the ground to distract the dogs from their meal. As the dog rushes over to investigate, the crow flies over to the bowl and scarfs the food while the pet is still busy sniffing the item. Another, more daring, strategy crows use is to creep up behind eating dogs and yank their tails. The birds then lead the enraged dog away from its bowl, out of the backyard, and onto the street. Then they fly back into the yard to eat the food while the hapless dog continues looking for the crow outside.

  On the other side of the Pacific, the crows of Seattle have learned to use architecture to their advantage by deliberately chasing sparrows into windows to knock them out. It’s not a perfect strategy, however. Sometimes the sparrows make a sharp turn just before hitting the glass and the pursuing crow slams into it instead.

  Corvids have also become familiar with our trash. In Juneau, Alaska, a pair of ravens figured out how to dispense whipped cream out of an aerosol can. One would use its beak to spray the cream while the other ate, after which they would swap places.

  Some crows even recognize the corporate brands amid our garbage. In one test, crows were presented with two brown paper bags filled with french fries. The only difference between the two bags was that one was plain while the other sported a McDonald’s logo. Time after time the crows opted for the McDonald’s bag first.

  Crows also use automobiles to their advantage. In San Francisco, American crows work together to drive flocks of pigeons into highspeed interstate traffic, so that they get hit by cars and buses. The crows then feed on injured or dead roadkill pigeons. Never has the term “a murder of crows” seemed more apt.

  The carrion crows of the Japanese city of Sendai have another roadside strategy. In autumn they like to eat walnuts but can’t break the tough shells with their beaks, so they learned to crack the nuts by dropping them from a great height onto the hard road surface. It worked OK, but then the crows noticed that having walnuts run over by cars is even more effective and refined the strategy. Now they sit on power lines above intersections and drop the nuts into the path of the waiting traffic so the nuts get crushed when the lights turn green. Once the lights revert to red, the crows swoop down to safely retrieve the freshly cracked nuts.

  Corvids may be the birds that understand how best to use roads, but other birds have also figured out that traffic can work to their advantage. Among them is the marabou stork, a strong contender for the title of the world’s ugliest bird. No one will be asking these African storks, also known as the undertaker bird, to deliver babies anytime soon. They look as if they’ve escaped out of someone’s nightmare. They stand five feet tall and have huge blue-gray wings, but when stomping around on the ground they hunch themselves up so their sharp swordlike beaks rest on the wobbly, inflatable sacs of bare pink flesh that dangle from their necks.

  Their calls are a mix of chilling clattering noises and grunts, and their dark-gray legs usually appear white because they are covered in the stork’s own excrement, which helps the birds stay cool in the hot sun. The bald scalps of their featherless heads help them stay clean when tearing flesh from the rotting carcasses that form much of their diet. Not that they only eat the dead. They often prey on other animals, swallowing live turtles whole and even taking down young flamingoes in the lakes of Africa.

  They are graceful fliers though, so that balances things out.

  The marabou stork’s natural home is savannah and grassland, but they are common sights in many African cities. In the fast-growing Kenyan capital of Nairobi, marabou storks nest in the thorny fever trees that line the busy Uhuru Highway close to the Nyayo National Stadium. It’s a handy spot for picking up roadkill or for paying a visit to the city’s slaughterhouses. The storks also turn up at the miserable Dandora garbage dump on the edge of the city, where they join the estimated ten thousand people who spend their lives trawling through the filthy mountains of waste for anything they can eat or sell.

  Though the birds’ excrement has turned the sidewalk of the Uhuru Highway rusty white, the marabou stork is largely welcomed in Nairobi. Rather than seeking to expel them, the Kenya Wildlife Service regards them as unpaid cleaners, who help to keep the streets free from muck.

  Birds do not just come to cities for the food. They also come for the weather.

  Cities have powerful effects on the local environment, and one of the most startling is the urban heat island effect. This phenomenon can make city centers as much as twenty-two degrees Fahrenheit hotter than the rural areas surrounding them. The effect is the result of replacing vegetation and soil with buildings, roads, and sidewalks. First, the removal of vegetation means the cooling effect of the water vapor released by plants and the shade offered by trees is lost. Then there are the concrete and asphalt surfaces that replace the natural flora. These materials absorb rather than reflect sunlight. During the day they soak up sun rays, storing them as heat that is then released at night. It’s like a battery that charges in the day and releases its energy at night.

  Traffic, industry, and air conditioning also play a role, pumping out more heat, while buildings block out cooling winds. In dense city centers filled with skyscrapers, the heat island effect can be even greater, because glass windows concentrate the light onto the street below and the heat released at night becomes trapped, boxed in by buildings on all sides.

  The urban heat island effect isn’t universal. In fact, the exact opposite happens in cities like Phoenix and Abu Dhabi, where irrigation makes them cooler than the hot desert around them. But for most cities, the urban heat island effect is at work, dialing up the temperature.

  The extra heat has a noticeable impact on life in the city. Plants flower earlier and insects become active earlier too—which is great news for the birds that eat them. In the wine-making city of Zielona Góra in western Poland, researchers found that black-billed magpies start building nests and laying eggs earlier than those outside the city, thanks to the supply of food and the warmth. As a result, the city’s urban magpie population was growing three times faster than the rural population.

  City lights produce similar effects, with blue tits laying eggs a day or two earlier in areas with streetlamps. Light also causes birds to start singing earlier in the morning and later at night, an effect that is more pronounced on cloudy days when more of the urban light is reflected back toward the ground.

  So far, so good, then, for the urban birds. They can feast on our bird feeders, raid our trash, and forage on our dumps. They also get to enjoy a warmer climate and get to stay up later thanks to the lights. But these benefits come at a cost: noise.

  Cities are noisy places, filled with the din of traffic, the sound of construction, and the bustle of people. Some areas are exceptionally noisy. Not least the Champs-Élysées in Paris, where the traffic thunders past at an ear-splitting eighty decibels. For urban songbirds, overcoming the blare is vital. If they can’t make themselves heard above the traffic, they could miss out on attracting a mate, fail to hear their chicks crying for food, or not hear another bird’s warning of a predator.

  Songbirds have come up with different strategies for dealing with the noise. Some resort to singing when the city is quiet. In the Spanish city of Seville, house sparrows and spotless starlings sing early to avoid the rush-hour traffic. Blue tits, European blackbirds, and European robins do the same.

  Others pump up the volume. One bird that does this is Australia’s noisy miner, a gray-bodied bird with yellow patches next to its eyes that make its eyeballs look bigger than they really are. As their name suggests, these honeyeaters are loud birds at the best of times, but when they take up residence along the busy arterial roads of Melbourne, which carry more than five thousand vehicles a day, they get even louder. In some cases noisy miners drown out the traffic by letting out alarm calls at a whopping ninety decibels.

  Traffic also forces birds to change their tunes. Most urban noise consists of low-pitch sounds, so birds often sing higher to avoid havi
ng their lower notes missed in the cacophony. It’s a strategy favored by great tits, which also sing shorter and faster songs in cities.

  But cities are not just loud, they get louder over time, as the male white-crowned sparrows of the Presidio of San Francisco know all too well. Since 1969 these birds, which despite their name have black and white stripes on their heads, have been trapped in a melodic arms race with the growing noise from the Golden Gate Bridge. To cope, the brown-winged birds have been singing higher and higher as they try to avoid being drowned out by traffic.

  The resulting tune has changed so much that the sparrows no longer recognize the songs they sang back when hippies rather than techies roamed the San Francisco streets. When researchers played them recordings of their present-day songs, the birds reacted as if it was an intruding rival, but they paid no attention at all to the songs they sang in the 1960s.

  Noise is not the only challenge for urban songbirds. The structure and architecture of cities plays havoc with their songs, which bounce off glass, get dulled by pavement, and echo around buildings. The sonic interference from the artificial surfaces and buildings means songbirds face the risk that their songs will get distorted, missed, or canceled out altogether.

  To deal with urban acoustics, birds adjust their songs to take account of the artificial surfaces. Often their response reflects how high or low they usually sing. In Washington, DC, and Baltimore researchers examined how the songs of six songbirds changed in response to how built-up the local area was. They found that gray catbirds and Northern cardinals sang higher to avoid the low notes of their songs while higher pitched singers, like the American robin and house wren, went the opposite way, cutting back on the top notes to compensate for the effect of urban surfaces.