Darwin Comes to Town

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Darwin Comes to Town Page 4

by Menno Schilthuizen


  Of the original 208 square miles of rainforest that clad the island two centuries ago, when the Sultan of Johor allowed the British to pitch their imperial tents, less than one square mile remains (in Bukit Timah and the Central Catchment). In addition, there are some eight square miles of “secondary” vegetation: the stuff that makes up most of those postage-stamp-sized bits of green on the map. Any organism that cannot live its entire life on bare concrete will need these green islands and islets to maintain itself in the city.

  But there’s a thing with islands—the smaller and more isolated they are, the less life they support. In the 1960s, entomologist Edward O. Wilson and theoretical ecologist Robert MacArthur famously crafted a new ecological theory that they called “island biogeography.” It went like this. Imagine a bunch of islands. These could be real islands in the sea but also any other fragments of habitat. The number of species (of, say, butterflies) that live on each island depends on two things: how many different butterfly species manage to reach the island, and how quickly butterfly species tend to become extinct there. The smaller the island and the farther away it is from the mainland, the more likely it is for a butterfly to flutter by and not settle there. But when a species does colonize it, its survival also depends on the size of the island. On a big island, the population can grow to, perhaps, thousands of individuals and the survival of the species is quite secure. But on a small island there may only be space for two dozen individuals of the species, and a heatwave or a disease could easily wipe them out. All these effects combined, Wilson and MacArthur discovered, produce a set of mathematical rules that make the number of species on an island surprisingly predictable. Roughly, with every tenfold increase in island size, the number of species you find there doubles. This goes for butterflies just as well as for beetles, bugs, and birds.

  A large town or city, with its archipelagos of green in oceans of asphalt, is an island biogeographer’s paradise. In the town of Bracknell in the UK, for example, ecologists studied the Hemiptera (a group of mostly plant-feeding insects including “true” bugs, aphids, and cicadas) living in the circular bits of vegetation in the centers of traffic roundabouts. These road islands lying in seas of tarmac followed island biogeographic theory to the letter, showing a perfect relationship between roundabout size (which ranged from 4,300 to nearly 65,000 square feet) and numbers of hemipteran species.

  Constructing road islands is one way in which cities can create archipelagos. But expanding cities also create islands by shredding up existing forests. This is one reason why urban ecosystems contain just a small subset of the species that lived there before. In an article in Nature in 2003, Australian ecologist Barry Brook, with Navjot Sodhi and Peter Ng of Singapore’s Lee Kong Chian Natural History Museum, enumerated precisely what had happened to Singapore’s flora and fauna since the start of urbanization in the early nineteenth century. Thanks to Victorian-era collectors such as Alfred Russel Wallace and Stamford Raffles, as well as learned societies like Singapore’s Nature Society (founded in 1954), we know a lot about the city’s natural history. Indeed, much of its nature is history. As Brook, Sodhi, and Ng found out, over the past two centuries or so, as the erstwhile continuous rainforest was logged, converted, and fragmented, species disappeared from the island one by one. The huge tiger orchid, the largest orchid in the world, was last seen around 1900, while tigers themselves left the island for good when the last one was shot in 1930. The Great Slaty Woodpecker disappeared in the second half of the twentieth century. Today, depending on the type of plant or animal, 35 to 90 percent of the original species has gone, or survive only under strict husbandry in Singapore Zoo and the Singapore Botanic Gardens.

  We park the car at the Sustainable Singapore Gallery and walk across the Marina Barrage to the Marina East Park on the other side. There, we take the concrete track that winds among the recently cut turf. Large dragonflies are zigzagging above the grass, targeting the clouds of midges that are beginning to gather in the setting sun. A public greens worker in an orange vest and a paddy hat uses his smartphone to document his impeccably mowed lawn, then gets on his all-terrain bike and cycles off. Here and there, the dried and broken carcasses of large black-and-yellow millipedes lie on the cycle path, the victims of failed attempts to cross the scorching concrete. It’s Anoplodesmus saussurii, another exotic species, says Sow-Yan.

  We take a right on a sand path that leads through a strip of coastal scrub onto an expanse of reclaimed land, offering a view of the scores of ships moored offshore. A group of bird-watchers with telescopes and binoculars is gathered at the far end of the spit of land. “We have about 2,000 bird-watchers in Singapore,” Sow-Yan says. “Also a few hundred people working on butterflies and dragonflies. And some shell enthusiasts, but not enough.” Sow-Yan pulls out his binoculars. “What are they looking at?” he mumbles, as he watches the bird-watchers closely. “Ha! They’re watching a house crow!”

  Twelve urban twitchers with high-end equipment observing a single invasive urban bird. It’s a familiar sight among urban naturalists all over the world. Like anybody else, biologists, whether professional or amateur, tend to live in cities. It is there that we also find the libraries, natural history collections, and nature clubs. With such concentrations of knowledge and interest in biodiversity, it is perhaps not surprising that the city is one of the best studied habitats in the world. It is also where emotions about our fellow species tend to flare. As the house crow guides us into the world of urban nature study in the next chapter, prepare for a tale of passion, tragic death, and politically motivated killings.

  4

  URBAN NATURALISTS

  Singapore is not the only city in the world to have been invaded by house crows. Humans have been transporting them throughout much of the tropics, either intentionally (as honorary “garbage-collectors” or for pest control) or accidentally, as stowaways on ships. Besides Singapore, they now live in many other countries in Southeast Asia, as well as the Middle East and East Africa. In fact, they don’t have a non-urban habitat anymore, and are exclusively found in towns and cities in the tropics. As bio-philosopher Thom van Dooren writes, “You might say that, in so far as these birds have a ‘natural environment,’ we’re it.”

  But in 1994, something momentous happened. A male and female house crow turned up 52 degrees north of the equator, in the port of Rotterdam, possibly by way of a cargo ship from Egypt. Surprisingly, the tropical crows survived the cold winter of 1996–97, when temperatures in the Netherlands dropped as far as minus 20 degrees Celsius, and in the following year even produced a nest with chicks. From then on, the population grew into a breeding colony in trees around a soccer field, where the birds built nests lined with colorful nylon strings that they would pull from discarded shipping rope in the port, and fed their chicks with fish and chip scraps pilfered from the portside “Het Vispaleis” fish stall. By 2013, there were about thirty of them, and bird-watchers would regularly come down to the port to add the sleek crow species to their “life list.”

  It remains a mystery how birds that normally breed in the hottest parts of the globe can suddenly shift their niche poleward. The urban heat island probably helped, and the milder climate near the seashore. But still—we will come back to this and similar mysteries later. Let us first examine the sad fate of this interesting population. Not everybody was as kindly disposed to them as the local naturalists.

  The provincial government, for one, certainly was not. Alarmed by the crow’s reputation of becoming a pest wherever it settled, it ordered for the birds to be exterminated, much to the dismay of many of Rotterdam’s bird lovers. Initially, the plan was successfully challenged by an animal welfare NGO on the grounds that the bird had, somehow, managed to get itself listed as legally protected. The authorities then proceeded to have its protected status annulled and in 2014 a new court ruling cleared the road for a professional hunter to be hired for culling all the birds.

  But extermination proved easier said than done. The
hunter found the inhabitants of Hoek van Holland on his path, who organized themselves in a “Save the House Crow” committee and vehemently protested against his avicidal intentions. The fact that the hunter accidentally shot some native Corvus monedula jackdaws (“they look really, really similar,” he complained to the Dutch newspaper Algemeen Dagblad) certainly did not help. Moreover, the house crows were smarter than anticipated. As he bagged his first birds, the other crows immediately became wary. “As soon as they see my car, I can already hear their alarm calls. Those birds are so damn clever.”

  Two years down the line a stalemate seems to have been reached—the hunter trying to outsmart his prey by arriving in his wife’s miniature car or by donning a funny red hat to avoid recognition, and a diminishing number of crows managing to cheat death by quick evasive action. Still, after repeated hunts and many an air rifle shot, most of the birds have perished and are now stored in the Rotterdam Natural History Museum. But rumor has it that a few are still at large. However, it is hard to get any reliable information on how many—if any—are left and exactly where they are. The Dutch website waarneming.nl, where naturalists can record their sightings of wildlife, is no longer releasing any for the house crow, so as not to play into the hands of the hunter, and the Facebook group devoted to the crow situation is similarly taciturn. So, when I approach Sabine Rietkerk of the Save the House Crow committee, in preparation for my own jaunt down to Het Vispaleis, I am met with the usual suspicion when inquiring about the whereabouts of a fugitive. In a lengthy exchange on Facebook, I am able to convince her of my good intentions and that I am not a front for the hunters. Initially she will not admit that there are still house crows living in Hoek van Holland, but eventually confides that the few surviving birds are no longer hanging at Het Vispaleis, but have cunningly shifted to a safer place. “They are hiding among the people … where the hunters cannot get at them. Try your luck in the shopping center,” she tells me.

  So one summer morning I find myself on expedition in the commercial hub of Hoek van Holland, the portside suburb of Rotterdam and the house crows’ ’hood. A few cafés, a newsagent’s, two supermarkets engaged in cutthroat competition, and a liquor store encircle a windswept square lined with closely-cropped elm trees. With my binoculars at the ready, I initially spot only jackdaws and herring gulls. But then, as I take a second lap around the square, one lonely, unmistakeable Indian house crow (identical to the ones I saw in Singapore only weeks before) is stepping across the road among the shopping-bag-toting pedestrians, right in front of me. Striding, more like. Long legs with a deliberate setting down of the feet, a graceful metallic-black body and a silvery brownish-gray hood, high forehead and a long beak. I manage to sneak a quick snapshot of it before it hops onto the pavement, takes a rustling bound into the branches of an elm tree, and disappears from sight. Its tree is right next to the terrace tables of one of the cafés, so I sit down and order a cup of coffee. The crow, hiding among the foliage next to me, is calling alternatingly in a raw and in a melodious metallic voice. Via Facebook, I send my snapshot to Sabine Rietkerk, who replies instantly: “Ah, good you found it. Yes, that one is often in that spot. He’s very vocal. And isn’t he beautiful?”

  A few hours later, in the collection depot of the Rotterdam Natural History Museum, I am looking down into a cardboard specimen box with the twenty-six stuffed, stretched-out and neatly labeled Rotterdam house crows that met with the government marksman’s lead pellets. Probably siblings, parents, uncles, and aunts of the one I saw sauntering across the street that same morning. Lying there stiff and side by side in their glossy black plumage, they look like body bags after a gang war. “They are beautiful,” agrees museum director Kees Moeliker. “It’s a sad tale, of course, what’s happening there in Hoek van Holland. They’re hunted down for political, not ecological reasons. But we’re happy that we managed to persuade the authorities to deposit the killed birds in our museum—otherwise they would just have destroyed them, I guess. It’s the only European population of this species, after all. Quite special, and splendid material for research.”

  The crows are the latest addition to the museum’s growing collection of urban natural history specimens. Moeliker takes me to a steel rack full of stuffed foxes, wrapped in clear plastic to keep out the insects. Over the past ten years, foxes have begun entering the city from the surrounding countryside, and whenever one is hit by a car, it ends up as a fine specimen in the museum’s depot. Of one recent acquisition, the stomach contents were also preserved by the diligent museum curators. They display, in a single five-course meal, this particular fox’s transition from a rural to an urban diet: rose hips, a small rabbit, an apple, doner kebab, and cherries in thick syrup.

  Conversely, the museum also pays particular attention to species that are disappearing from the city, like the red squirrels that used to live in the Kralingse Bos, the city’s largest park, but became extinct in the 1990s. Moeliker holds up a stuffed squirrel, pinned clumsily to a piece of tree branch stuck to a plank. “A few years ago, an old lady brought us this. Normally, we don’t really welcome this kind of decorative item, but she told us it had been found dead in the Kralingse Bos in 1966. It’s the only specimen we have of the time that the population was still alive and well. So that’s kind of nice.”

  Up in the public exhibition of the museum, the theme of urban nature is unleashed with even more abandon. One showcase holds nests that urban swans and pigeons built from plastic bottles, chunks of polystyrene, chicken wire, and rubber bands—which in some parts of the city are much easier to come by than genuine branches and twigs. Another one has displays of the surprising diversity of moth species found in the city center. Also on view are herbarium specimens of wildflowers that normally grow on the saline seashore, but that now live along the city’s roadside verges thanks to winter salting; and of plants whose natural home are rocky ledges in the southern-European mountains, but that now also thrive among the stony walls of Rotterdam’s heat island.

  The blockbuster, however, is the exhibit Dead Animal Tales, a row of showcases in the museum’s central hall, which hold meticulously mounted specimens of city animals that collided head-on with their human cohabitants in a particularly memorable way. The McFlurry-hedgehog, for example, is a hedgehog (Erinaceus europaeus) that met its demise when its head got stuck in the hole in the top of a plastic McFlurry soft serve ice-cream cup—and is mounted in precisely that undignified position. It is just one of many similar hedgehog victims of this popular fast-food dessert. As the accompanying card explains, “Searching for leftover ice cream, the hedgehogs would get their heads in through the wide opening in the lids, but their spines stopped them from pulling out again. They would die from starvation or blindly walk into water and drown.” Another classic is a stuffed house sparrow (Passer domesticus) next to a plastic butter tub with the words “domino sparrow” written across in black marker pen. In 2005, this particular sparrow managed to sneak into a hall where 4 million domino tiles had been set up for a live televised event called Domino Day. By the time the panic-stricken sparrow had knocked over 23,000 of them, it was decided that this had to end, and a guy with a gun (in fact, the same professional sharpshooter who is now the house crows’ nemesis) did the honors. Once again, the museum’s display card text is unsurpassable, so I quote: “The death of the sparrow sparked major commotion (and commotion about the commotion). […] After intense lobbying […] the museum was able to acquire the dead sparrow and the butter tub in which it was kept.”

  Not only is the museum a central repository for the urban flora and fauna of Rotterdam, it is also a hub for every Rotterdammer who wishes to devote him or herself to one particular sliver of the city’s biodiversity. Like everywhere in the world, this demographic is rapidly growing. Cities are full of passionate people who build insect collections and herbariums, or document butterflies, plants, and birds with the cameras on their smartphones, logging their observations on global “citizen science” Internet platforms
like Observado or iNaturalist. Or they may be activists and fight for the preservation of urban biodiversity hotspots, iconic ancient trees or rare species. In Rotterdam, there are various nature clubs in town (including single-issue ones such as Save the House Crow). And, says Moeliker, the museum’s Rotterdam Urban Ecology Unit maintains a large network of enthusiastic amateur naturalists.

  Some of those Rotterdam enthusiasts began as members of the local branch of the Royal Dutch Society for Natural History (KNNV), which was erected way back in 1917. Similarly, many big-city based nature societies all over the world date back to the early twentieth century or earlier. Dates of foundation for the Paris, Belfast, Bombay, and London natural history societies are 1790, 1821, 1883, and 1913, respectively—the urban naturalist is by no means a recent phenomenon. But, as Moeliker’s predecessor, former museum director Jelle Reumer, points out in his book Wildlife in Rotterdam, an interesting shift took place in nature clubs worldwide around the middle of the twentieth century. To illustrate this, Reumer takes the bibliography of Mannahatta, the book that accompanies Eric Sanderson’s Manhattan project that we came across in an earlier chapter. It lists field guides to New York’s biodiversity from the early nineteenth century until today. Prior to the mid-twentieth century, Reumer notices, the word “vicinity” almost without fail appears in the books’ titles: Synoptical View of the Lichens Growing in the Vicinity of New York (1823), The Frogs and Toads in the Vicinity of New York City (1898), Plants of the Vicinity of New York (1935). But from the late 1950s onward, such “environs”-indications were dropped from newly appearing titles: A Natural History of New York City (1959), Wild New York: A guide to the wildlife, wild places and natural phenomena of New York City (1997), Damselflies and Dragonflies of Central Park (2001) …

 

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