As high-rise cities grow upwards and outwards, increasing numbers of birds die by crashing into glass buildings each year. And of course many others break beaks, wings, and legs, or suffer other physical harm. But we can help eradicate the danger by good design.
Most research into building-related bird deaths has been done in the United States and Canada, where cities such as Toronto and New York City are located on bird migration paths. In New York City alone, the death toll from flying into buildings is about 200,000 birds a year.
Across the United States and Canada, bird populations have shrunk by about three billion since 1970. The causes include loss of habitat and urbanization, pesticides, and the effects of global warming, which reduces food sources.
An estimated 365 million to one billion birds die each year from “unnatural” causes like building collisions in the US. The greatest bird killer in the U.S. remains the estimated 60 to 100 million free-range cats that kill up to four billion birds a year.
But rampant global urbanization is putting the reliance on glass buildings front of stage as an “unnatural” cause of bird deaths, and the problem is growing exponentially.
In the line of flight
Most birds fly at around 18 to 30 miles an hour, with falcons capable of up to 124 miles per hour. When migrating, birds generally spend five to six hours flying at a height of 492 feet, sometimes much higher.
And that’s where the problems start with high-rise buildings. Most of them are much taller than the height at which birds fly. The paradigm of high-rise gothams, New York City, has hundreds of skyscrapers, most with fully glass, reflective walls. One World Trade is 1,776 feet tall, the 1931 Empire State is 1,250 feet (although not all glass), and even the city’s 100th-highest building, 712 Fifth Avenue, is 650 feet.
To add to the problems of this forest of glass, the city requires buildings to provide rooftop green areas. These attract roosting birds, which then launch off inside the canyons of reflective glass walls—often mistaking these for open sky or trees reflected from behind.
A problem of lighting and reflections
Most cities today contain predominantly glass buildings—about 60% of the external wall surface. These buildings do not rely on visible frames, as in the past, and have very limited or no openable windows (for human safety). They are fully air-conditioned, of course.
Birds cannot recognize daylight reflections, and glass does not appear to them to be solid. If it is clear, they see it as the image beyond the glass. They can also be caught in building cul-de-sac courtyards—open spaces with closed ends are traps.
At night, the problem is light from buildings, which may disorientate birds. Birds are drawn to lights at night. Glass walls then simply act as targets.
Some species send out flight calls that may lure other birds to their death.
Birds see ultraviolet light, which humans cannot. Some manufacturers are now developing glass with patterns using a mixed UV wavelength range that alerts birds but has no effect on human sight.
New York City recently passed a bird-friendly law requiring all new buildings and building alterations (at least under 75 feet tall) be designed, so birds can recognize glass. Windows must be “fritted” using applied labels, dots, stripes, and so on.
The search is on for various other ways of warning birds of the dangers of glass walls and windows.
Combinations of methods are being used to scare or warn away birds from flying into glass walls. These range from dummy hawks (a natural enemy) and actual falcons and hawks, which scare birds, to balloons (like those used during the London Blitz in the Second World War), scary noises, and gas cannons—and even other dead birds.
Researchers are using lasers to produce light ray disturbance in cities, especially at night and on dark days.
Noise can be effective, although birds do acclimatize if the noises are produced full-time. However, noise used as a “sonic net” can effectively drown out bird chatter and that interference forces them to move on looking for quietness. The technology has been used at airports, for example.
A zen curtain developed in Brisbane has worked at the University of Queensland. This approach uses an open curtain of ropes strung on the side of buildings. These flutter in the breeze, making patterns and shadows on glass, which birds don’t like.
These zen curtains can also be used to make windows on a house safer for birds. However, such a device would take some doing for the huge structures of a metropolis.
More common, and best adopted at the design phase of a building, is to mark window glass, so birds can see it. Just as we etch images on glass doors to alert people, we can apply a label or decal to a window as a warning to birds. Even using interior blinds semi-open will deter birds.
Birds make cities friendlier as part of the shared environment. We have a responsibility to provide safe flying and security from the effects of human habitation and construction, and we know how to achieve that.
Norman Day is a lecturer in architecture, practice and design at Swinburne University of Technology. This article is republished from The Conversation under a Creative Commons license. Read the original article.