Vesper Flights. Helen MacDonald
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, we detect a smear of black at its chest and a distinctive pattern on its tail: a male yellow-rumped warbler. It flickers past and disappears around the corner of the building. A little while later, we see another flying the same way. Then another. It dawns on us that this is the same bird, circling. Another one joins it, both now drawn helplessly towards and around the light, reeling about the spire as if caught on invisible strings. Watching them dampens our exuberant mood. The spire is lit with pulsing rivulets of climbing colour like a candle tonight to mark the building’s eighty-fifth anniversary. And these birds have been attracted to it, pulled off course, their exquisite navigational machinery overwhelmed by light, leaving them confused and in considerable danger. After being mesmerised in this way, some birds drag themselves free and continue their journey. Others don’t.
New York is among the brightest cities in the world after Las Vegas, only one node in a flood of artificial illumination that runs from Boston down to Washington. We cherish our cities for their appearance at night, but it takes a terrible toll on migrating songbirds: you can find them dead or exhausted at the foot of high-rise buildings all over America. Disoriented by light and reflections on glass, they crash into obstacles, fly into windows, spiral down to the ground. More than a hundred thousand die each year in New York City alone. Thomas King, of the New York pest-control company M&M Environmental, has had calls from residents of high-rise buildings asking him to deal with the birds colliding with their windows during migration season. He tells them that there’s no solution, but they can talk to their building manager about turning off the lights. It helps. Programmes like New York City Audubon’s ‘Lights Out New York’ have encouraged many high-rise owners to do the same, saving both energy and avian lives.
Every year the ‘Tribute in Light’ shines twin blue beams into the Manhattan night as a memorial to the lives lost on September 11. They rise four miles into the air and are visible sixty miles from the city. On peak migration nights songbirds spiral down towards them, calling, pulled from the sky, so many circling in the light they look like glittering, whirling specks of paper caught in the wind. On one night last year, so many were caught in the beams that the few pixels representing the ‘Tribute’ site glowed super-bright on the radar maps. Farnsworth was there with the Audubon team that got the lights shut off intermittently to prevent casualties. They switched off the ‘Tribute’ eight times that night for about twenty minutes at a time, releasing the trapped birds to return to their journey. Each time the lights went back on, a new sweep of birds was drawn in – the twin towers made ghosts of light visited over and over by winged travellers intermittently freed into darkness before a crowd rushed in to take their place. Farnsworth is a lead scientist in BirdCast, a project that combines a variety of methods – weather data, flight calls, radar, observers on the ground – to predict the movements of migrating birds throughout the continental United States and forecast big nights like this that might require emergency lights-out action.
The flow of birds over the