THE Federal Bureau of Investigation has a spectacular view of the city skyline from its Chicago office tower. But when special agent Julia Meredith arrived at work one Monday morning, her eyes were focused firmly on the ground. That’s where the bodies were – more than 10 of them.
Some of the dead were Blackburnian warblers, birds with bright yellow and orange plumage that are rarely seen in the city. They had been on their way to their wintering grounds in South America when they had collided with the building’s glass facade. “They had come all this way and here they were, dead,” says Meredith.
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It’s not an isolated incident. Just last month, in one building strike in Galveston, Texas. The world over, wherever humans are extending their buildings, machines and light into the sky, the lives of aerial creatures are at increasing risk. We don’t have very accurate figures, but in the US, casualties . Yet while efforts to protect areas on land and in water have accelerated since the 1970s, the sky has been almost entirely ignored.
That could be about to change if a new wave of conservationists have their way. They want to reclaim the air for its inhabitants, creating protected areas that extend into the sky and designing buildings to avoid death. If this noble aim is to succeed, however, we must first address a more fundamental question: what exactly is it that we are protecting?
A huge range of creatures are at home in the air. Along with the thousands of bird species that flit from perch to perch, there are others, such as the albatross and Alpine swift, that spend much of their life aloft. Bats, mostly nocturnal fliers, often dine on the myriad insects that share their airspace. Millions of other insects, from butterflies to beetles, occupy the skies by day. Ballooning spiders are at the mercy of winds that catch long trails of web and carry them far from home. Microbes, winged seeds and spores are also all transported on the breeze, and can travel hundreds or thousands of kilometres.
If we ever consider the aerial ecosystem occupied by these creatures, we tend to think of it as one vast expanse of sky. “The minute they take off into the air, we don’t really have a mechanism in place to define that habitat type. But it’s really critical,” says Christina Davy at Trent University in Ontario, Canada.
Earlier this year, as a first step to protecting the biodiversity of airspace, Davy, along with Kevin Fraser at the University of Manitoba and Adam Ford at the University of British Columbia, that we should think about aerial habitats as layers, similar to the way that marine habitats are characterised by depth. They propose three subdivisions of the troposphere, the lowest zone of the atmosphere rising to roughly 15 kilometres up. The basoaerial habitat extends from the ground up to 1 kilometre. Here human threats range from tall buildings to wind turbines and moving vehicles (see diagram). The mesoaerial habitat, between 1 and 8 kilometres in altitude, is characterised by steadily decreasing temperatures and oxygen levels; the main threats here are light pollution and aircraft. In the epiaerial habitat, between 8 and 13 kilometres up, temperatures plunge towards -56°C at mid-latitudes; its inhabitants, mainly microorganisms, require special adaptations to survive.
“In the US, bird casualties are probably in the hundreds of millions every year”
A better definition of habitats is only part of what’s needed if “aeroconservation” is to take off, however. For a start, we’re not even really sure how big the problem is we’re trying to solve. A meta-study published in 2014 put the number of birds killed in building collisions at and 968 million a year in the US. It is estimated that 140,000 to 328,000 birds are and . In the UK, the British Trust for Ornithology estimates that 100 million birds crash into windows annually, and in Canada, more than 50 million adult birds are thought to die each year from collisions with buildings, wind farms, communication towers and other human structures that invade the skies.
On their own, though, such numbers only say so much. “What we have are mortality counts,” says Davy. “We don’t have the data that we need to be able to say whether [such counts equate to] 1 per cent or 100 per cent of the population.” That’s because we just don’t know how many creatures call the sky home.
For birds, efforts to estimate populations are well under way, aided by decades of counts, ringing schemes and newer methods such as tracking with telemetry and GPS. But for other airborne creatures, we are further in the dark. Population estimates for bats are often murky or non-existent. Some early attempts to quantify insects, meanwhile, have produced staggering numbers: more than a , for example.
Numbers are one thing; behaviour is another. “We can’t track three-dimensional locations of small organisms for any distance because it’s too hard to put a tracking device on them,” says Robb Diehl, an ecologist with the US Geological Survey who uses radar to study migratory birds.
In the past, we have rarely looked at how aerial species move in 3D “because it’s easier to do in 2D”, says Sergio Lambertucci at the National University of Comahue in Argentina. Tools such as accelerometers and GPS are changing that. Progress is being made in charting the behaviour of larger animals, including bats, and Lambertucci is using the technology to study several raptor species, Andean condors among them.
Until we know more, it is hard to judge the effects of our airspace incursions. But we can look at how animals in other ecosystems are affected by our activities and apply these lessons to the sky. On land, habitat fragmentation has detrimental impacts on living things, for example. In aerial habitats, this could take the shape of animals making long detours to avoid tall buildings and cities, or being lured into spending time circling light sources while travelling at night. “What are the costs of that movement to migration duration, energetic reserves and fitness once they get to their breeding sites?” asks Ford.
Seeing the light
Light pollution, in particular, could have a big impact in all three aerial zones. “You can see light from outside of our atmosphere,” says Travis Longcore at the University of Southern California, . Many studies have reported effects such as seabird chicks becoming disoriented by overhead lights on their first flight out to sea and crashing. aims to find out the thresholds at which artificial light levels begin to affect the navigation, dispersal, communication and reproduction of different species, get a handle on the size of those effects and determine the size of dark refuges needed to maintain natural ecosystem processes.
Computer modelling is helping to quantify the whole-population effects of both artificial light spilling skyward and, more generally, our structural cluttering of the air. Projections for hoary bats, the species most frequently killed by wind turbines in North America, for example, suggest lethal collisions with blades over the next century, seeing them decline by as much as 90 per cent.
Given the ubiquity of our aerial incursions, why hasn’t the idea of protecting aerial habitats come to our attention earlier? “We are terrestrial creatures,” says Diehl. “In our evolutionary history, we’ve lived off the land and, to some extent, out of the water.” He suspects that our notions of habitat are deeply ingrained and, like our science, oriented towards the landscape. We may need to step away from the biases of our senses and education to lift our gaze upwards. This offers the chance of some blue-sky thinking, says Diehl: the concept of aeroconservation is so novel that, in theory at least, .
One unknown in future efforts to protect airspace is whether it comes under the umbrella of environmental law. At the moment, even the way we define ecosystems works against aeroconservation. The International Union for Conservation of Nature, for example, recognises terrestrial, aquatic and “other” habitats, but doesn’t explicitly mention the air. This oversight extends to international policy such as the UN Convention on the Conservation of Migratory Wild Species of Animals. Neglect of airspace as habitat is problematic for creatures whose lifestyles include air travel, say Davy, Fraser and Ford.
Nevertheless, legal protection of airspace isn’t without precedent. No-fly or restricted zones for drones and aircraft exist, mainly above politically or militarily sensitive zones such as the centre of Washington DC. But a no-fly zone over wildlife habitat at the Boundary Waters Canoe Area Wilderness in northern Minnesota has existed since 1948 and restrictions are in place over parts of some to protect marine mammals and seabirds from disturbance.
Current laws have also been invoked by campaigners. Groups including the Toronto-based Fatal Light Awareness Program have been drawing attention to bird-building collisions and rescuing injured birds for decades. “But the biggest shift came when we found ourselves as witnesses in a court of law,” says executive director Michael Mesure.
That case, in 2010, was brought in Canada by environmental law charity Ecojustice against Cadillac Fairview, a commercial property owner and manager, after hundreds of migratory birds had died in collisions with its buildings’ mirrored windows in Toronto. The judge ruled that Ontario’s Environmental Protection Act and Canada’s Species at Risk Act prohibit reflected daylight from building windows, because the glass creates a mirage of habitat and sky, .
As a result, bird safety is now more commonly taken into account in the planning and construction of buildings in many Canadian cities. In addition, LEED – a popular green certification scheme for buildings worldwide – is piloting the inclusion of bird-friendly architecture in its points system for “green buildings”. Windows can be treated with special film, translucent tape or spaced wires to make them visible to birds. Avoiding positioning outdoor plants near windows may also help. But all windows reflect daylight and although the laws of Ontario say they shouldn’t, in practice this isn’t being enforced – and it is unclear how it could be.
Invoking building codes is no panacea. In Canada, more than after colliding with power lines, with raptors such as owls, kestrels and eagles particularly prone. This could be tackled by placing markers on wires to make them more visible, or putting them underground. Electrocution of birds that can straddle two power lines is also a big killer, particularly of Europe’s white storks. A possible solution is to increase the distance between wires.
“Anything we do is going to look better than a bunch of dead birds”
Progress is being made here: countries such as Germany require to be incorporated into the design of new and upgraded power lines. With wind turbines, the UN-sponsored is building protection measures into new wind energy projects along important migratory routes up through eastern Africa and the Middle East, including radar sensors that enable turbines to be when a flock is approaching.
As for addressing light pollution, aeroconservationists have a natural ally: the International Dark Sky Association. A movement founded by astronomers, its aim is to preserve some of Earth’s natural darkness. In some US national parks, retrofitting has already begun to reduce upward spillage of light. Commercial lighting companies are making changes too, although progress is slow, says Longcore.
While developments are small-scale and piecemeal for now, they are no less important for the creatures concerned. These include the Blackburnian warblers that migrate through Chicago each year. Though it took time to seek expert help and navigate the bureaucracy, Meredith eventually secured an FBI-approved plan: netting put up during the migration season now protects birds from the building that had been killing them. It may temporarily restrict the spectacular views, but Meredith is convinced it is a price worth paying. “Anything we do is going to look better than a bunch of dead birds,” she says.
This article appeared in print under the headline “The friendly skies”
