Vesper Flights. Helen MacDonald

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      Above us, LED bulbs around the base of the spire cast a soft halo of pale light up into the darkness. An incandescent blur of white skips across it. Through binoculars it resolves into a noctuid moth, wings flapping as it climbs vertically towards the tower. No one fully understands how moths like these orient themselves while migrating; there’s speculation that they might navigate by sensing Earth’s magnetic fields. This one is flying upward in search of the right airflow that will allow it to travel where it wants to go.

      Wind-borne migration is an arthropod speciality, allowing creatures like aphids, wasps, lacewings, beetles, moths and tiny spiders hoisted on strands of electrostatically charged silk to travel distances ranging from tens to hundreds of miles. These drifting creatures are colonisers, pioneers looking for new places to live, and they’ll make a home wherever they find one. Place a rose bush out on the arid environment of a top-floor balcony and soon wind-borne sap-sucking aphids will cluster on its stems, followed by the tiny wasps that parasitise them.

      Insects travel above us in extraordinary numbers. In Britain, the research scientist Jason Chapman uses radar systems aimed into the atmosphere to study their high-altitude movements. Over seven and a half billion can pass over a square mile of English farmland in a single month – about 5,500 pounds of biomass. Chapman thinks the number passing over New York City may be even higher, because this is a gateway to a continent, not a small island surrounded by cold seas, and summers here are generally hotter. Once you get above six hundred and fifty feet, he says, you’re lofted into a realm where the distinction between city and countryside has little or no meaning at all.

      During the day, chimney swifts feast on these vast drifts of life; during the night, so do the city’s resident and migrating bats, and nighthawks with white-flagged wings. On days with north-west winds in late summer and early fall, birds, bats and migrant dragonflies all feed on rich concentrations of insects caused by powerful downdraughts and eddies around the city’s high-rise buildings, just as fish swarm to feed where currents congregate plankton in the ocean.

      It’s not just insects up there. The tallest buildings, like the Empire State, One World Trade Center and other new super-towers, project into airspace that birds have used for millennia. The city lies on the Atlantic Flyway, the route used by hundreds of millions of birds to fly north every spring to their breeding grounds and back again in the fall. Most small songbirds tend to travel between three and four thousand feet from the ground, but they vary their altitude depending on the weather. Larger birds fly higher, and some, like shorebirds, may well pass over the city at ten to twelve thousand feet. Up here we’ll be able to see only a fraction of what is moving past us: even the tallest buildings dip into only the shallows of the sky.

      Though you can see migrating raptors soaring at altitudes well over eight hundred feet above the city during the day, most species of diurnal birds migrate after nightfall. It’s safer. Temperatures are cooler, and there are fewer predators around. Fewer, not none. Just before I arrived, Farnsworth saw a peregrine falcon drifting ominously around the building. Peregrines frequently hunt at night here. From high-rise lookout perches, they launch flights into the darkness to grab birds and bats. In more natural habitats, falcons cache the bodies of birds they’ve killed among crevices in cliffs. The ones here tuck their kills into ledges on high-rises, including the Empire State. For a falcon, a skyscraper is simply a cliff: it brings the same prospects, the same high winds, the same opportunities to stash a takeout meal.

      We stare out into the dark, willing life into view. Minutes pass. Farnsworth points. ‘There!’ he says. High above us is a suspicion of movement, right at the edge of vision where the sky dissolves into dusty chaos. I swing my binoculars up to my eyes. Three pale pairs of beating wings, flying north-north-east in close formation. Black-crowned night herons. I’ve only ever seen them hunched on branches or crouched low by lakes and ponds, and it’s astounding to see them wrenched so far from their familiar context. I wonder how high they are. ‘Those are pretty large,’ Farnsworth says. ‘When you look up into the light, everything looks bigger than it is, and closer than it is.’ He estimates that the herons are about three hundred feet above us, so they’re about one and a half thousand feet from ground level. We watch them vanish into darkness.

      I feel less like a naturalist here and more like an amateur astronomer waiting for a meteor shower, squinting expectantly into the darkness. I try a new tactic: focusing my binoculars on infinity and pointing them straight upwards. Through the lenses, birds invisible to the naked eye swim into view, and there are birds above them, and birds higher still. It strikes me that we are seeing a lot of birds. An awful lot of birds.

      For every larger bird I see, thirty or more songbirds pass over. They are very small. Watching their passage is almost too moving to bear. They resemble stars, embers, slow tracer fire. Even through binoculars those at higher altitudes are tiny, ghostly points of light. I know that they have loose-clenched toes tucked to their chests, bright eyes, thin bones and a will to fly north that pulls them onward night after night. Most of them spent yesterday in central or southern New Jersey before ascending into darkness. Larger birds keep flying until dawn. The warblers tend to come earlier to earth, dropping like stones into patches of habitat further north to rest and feed over the following day. Some, like yellow-rumped warblers, began their long journeys in the south-eastern states. Others, like rose-breasted grosbeaks, have made their way up from Central America.

      Something tugs at my heart. I’ll never see any of these birds again. If I weren’t this high, and the birds weren’t briefly illuminated by this column of light cast by a building thrown up through the Depression years to celebrate earthly power and capital confidence, I’d never have seen them at all.

      Farnsworth pulls out a smartphone. Unlike everyone else holding screens up here, he’s looking at radar images from Fort Dix in New Jersey, part of a National Weather Service radar network that provides near-continuous coverage of airspace over the continental USA. ‘It’s definitely a heavy migration night tonight,’ he says. ‘When you see those kinds of patterns on radar, in particular, those greens,’ he explains, ‘you’re talking about one thousand to two thousand birds per cubic mile potentially, which is almost as dense as it gets. So it’s a big night.’ After days of bad weather for birds wanting to fly north, with low cloud and winds in the wrong direction, a bottleneck of migrants built up, and now the sky is full of them. I watch the pixellation blossom on the animated radar map, a blue-and-green dendritic flower billowing out over the whole East Coast. ‘This is biological stuff that’s up in the atmosphere,’ Farnsworth says, pointing one finger to the screen. ‘It’s all biology.’

      Meteorologists have long known that you can detect animal life by radar. Just after the Second World War, British radar scientists and Royal Air Force technicians puzzled over mysterious plots and patterns that appeared on their screens. They knew they weren’t aircraft and christened them ‘angels’ before finally concluding that they were flocks of moving birds. ‘That was their contamination, right?’ Farnsworth says of radar meteorologists. ‘They wanted to filter all that stuff out. Now the biologists want to do the reverse.’ Farnsworth is one pioneer of a new multidisciplinary science, fit for an era in which weather radar has become so sensitive it can detect a single bumblebee over thirty miles away. It’s called aeroecology, and it uses sophisticated remote-sensing technologies like radar, acoustics and tracking devices to study ecological patterns and relationships in the skies. ‘The whole notion of the aerosphere and airspace as habitat is not something that has come into the collective psyche until recently,’ Farnsworth says. And this new science is helping us understand how climate change, skyscrapers, wind turbines, light pollution and aviation affect the creatures that live and move above us.

      At ten o’clock, cirrus clouds slide overhead like oil poured on water. Ten minutes later, the sky is clear again, and the birds are still flying. We move to the east side of the observation deck. A saxophonist begins to play, and in concert with this unlikely soundtrack we begin to see birds far closer than before. One, in particular. Though it is overexposed in the light, СКАЧАТЬ