Striking out: window collisions a growing threat to our birds
MOST OF US have experienced it at some time – the distressing thud that signals a probably fatal collision of bird and window. Such occurrences are a growing conservation concern; window collisions kill more birds than any other human-related factor except habitat destruction. Estimates suggest the number of birds killed like this globally each year could be in the billions.
Australian ornithological consultant Stephen Ambrose has spent almost two decades advising councils, architects and developers on how to improve building design to reduce the risk of bird strikes. Collisions, he explains, are mostly caused by birds trying to reach habitat they can either see through the window or reflected in it.
He adds that migratory species are particularly at risk, although the precise impact bird–window collisions are having on Australian species has yet to be studied in detail. One exception is the critically endangered swift parrot, the only bird species known to be adversely affected by window-strike mortality at the population level.
As its name suggests, the swift parrot is a fast flyer, typically travelling in flocks as it migrates from Tasmania to the south-eastern mainland of Australia. It tends to fly at or below tree-top level, which puts it at particular risk of window collisions. To make matters worse, its favoured mainland habitat is forested areas, and these happen to be where more and more homes are being built, increasing the chance of collisions.
It has been estimated that each year up to 2 per cent of the swift parrot breeding population – which is down to a mere 2000 or so birds – is killed as a result of collisions with windows, fences (especially chain-link fences) and vehicles.
Another species attracting concern is the powerful owl, which is threatened in New South Wales. “Recently there has been a significant increase in the number of powerful owl strikes in Sydney,” Stephen says. Again, the encroachment of residential development into bushland is exacerbating the problem.
Stephen is also concerned that “multiple high-rise buildings are being built near internationally important wetlands in major cities and towns in Australia”. This trend is likely to lead to an increase in incidents such as the one that saw an immature white-bellied sea-eagle killed in Sydney’s CBD after it collided with a tall building.
Disappearing natural habitat is also driving more birds into urban areas – a process that’s accelerated by our efforts to attract them. “Australians love landscaping their gardens, feeding birds and providing water baths for them,” Stephen says. “This, in turn, attracts birds to people’s gardens, which is fantastic.” The downside is that drawing birds into an urban environment increases the likelihood they’ll fly into a window at some point.
It’s not only windows that are a problem. Barriers erected to shield residents from the noise of busy roads are also a major issue. “There are reports of birds, especially parrots, smashing into the glass or fibreglass barriers in an attempt to reach the trees on the opposite side of the road,” Stephen explains.
“As a result, road architects and engineers now construct road barriers that are visible to wildlife.”
Stephen believes that attempts to reduce bird–window collisions are slowly gaining momentum in Australia. “Most architects and engineers are quite receptive to modifying their designs or using different building materials to reduce the risk, if it’s explained logically and sensibly,” he says. “It usually just involves tweaking things here and there, rather than major redesigns, which makes it easier to gain the support of the builders.”
There is still much room for improvement, however, particularly in regard to the design of major buildings in Australia’s cities.
“Many new high-rise and other large city buildings have lots of glass windows, and plaza areas are often landscaped with canopy trees and shrubbery,” Stephen says. “While many of these designs are aesthetically pleasing, they do increase the risk of birds striking glass panes.”
One key to reducing bird–window collisions is the development of bird-friendly glass products, which has been gathering pace in recent years. For example, US company Walker Textures has options under the AviProtek label, mostly involving acid-etching to mark the outside surface of glass. The markers use a 5/10 rule, with horizontal lines spaced up to 5cm apart and vertical lines less than 10cm apart (birds will try to fly through larger ‘gaps’). Other companies silk-screen then fire a ceramic compound onto glass to create patterns to deter birds.
The problem with such solutions is that the patterns on the glass can obstruct our view. So some manufacturers are trying to develop products with patterns birds can see but people can’t. The key to many is that birds can see ultraviolet (UV) light, but we can’t. However, birds differ in the kind of UV light to which their eyes are sensitive, so it’s important to use materials that reflect a broad range
of wavelengths in the UV spectrum.
Among the more promising is Ornilux, a new glazing system developed by German manufacturer Arnold Glas, with assistance from the Max Planck Institute for Ornithology in Starnberg, Germany. Inspired by the webs of orb-weaver spiders, which reflect UV light to stop birds flying through, the glass is coated with a mesh of UV-reflecting lines.
With many of Australia’s bird species already facing multiple threats, anything homeowners can do to reduce the risk of bird–window collisions is a big step in the right direction.
How you can help
1. If you’re building or renovating, use bird-safe glass for your windows.
2. For existing windows – particularly those facing garden areas – apply an external anti-reflective film, tape or string to deter birds.
3. Install fibreglass screening in front of windows. If mounted correctly (at least 13cm in front of the window with enough tension), most birds will bounce off them.
4. Place feeders either close to, or far away from windows.
5. Leave blinds partially open so a striped pattern is visible from outside. If you have curtains, close them.
6. If you have any ‘through-house’ lines of sight, block them with a curtain or blind, or by closing an internal door.
7. At night, use low-intensity lighting and direct light from lamps away from windows.
8. For a bird stunned by a collision, use gloved hands to gently pick it up and place it in a safe area away from any predators, in a well-ventilated box. Check it in an hour or so and release it outside when it’s alert.
9. Be part of BirdLife Australia’s Bird Strike Project, which is investigating the collision of birds with windows and cars. If you witness a bird strike record it here: birdsinbackyards.
