Anti-avian ingenuity: the numerous ways to minimise airport bird strikes

The widespread installation of wind turbines over the past three decades has generated a new ecologically unfriendly phenomenon, namely wild birds being killed by turbine sails. Although it could cause maintenance issues - and of course it's not good news for the birds themselves, the increasing density of air travel means far higher numbers of bird strikes are likely to occur in the much smaller turbines of jet engines, predominantly around airports.

I've previously written about how urban environments appear to generate wildlife somewhat smarter than rural equivalents. In contrast, airports seem to be a very poor choice for birds to inhabit, suggesting that the loss of natural environments coupled with the relatively undeveloped land around airport perimeters is causing birds to congregate in such precarious places.

It's somewhat ironic that such an environmentally unfriendly technology as air travel is inadvertently providing habitats for wild birds, but as urban sprawl increases animals are forced to live wherever they can find, even areas as seemingly unsuitable as runway taxiways and safety areas. As aircraft increase in size and speed but decrease in engine noise, it may be that aviation technology is contributing to the problem. In addition, waterfowl are attracted by the fresh water storage ponds found near runways for use in firefighting or drainage. Therefore, despite the noise, pollution, changes to local weather patterns and the obstacles in the form of the aircraft themselves, airports worldwide have found themselves becoming home to or visited by flocks of numerous bird species.

With over forty bird strikes every day, the cost to the global airline industry surpasses US$1 billion per year. So what is being done to reduce or remove this threat? The range of options is both ingenious and proof that birds are a formidable opponent, so here is a brief summary of popular methods:

1. Removing food and water sources
2. Audio repellents
3. Chemical repellents
4. Fake fire and pyrotechnics
5. Baited traps
6. Real and fake predators
7. Removing and culling birds

1) Reducing bird foodstuffs involves a variety of techniques that aren't exactly the height of eco-friendliness. Any vegetation that might be a food source for local bird species, such as fruit- or seed-bearing trees and bushes may be removed. One step further is to replace any grass areas with a non-local variety that is less attractive to native birds.

A substantially less environmentally-friendly approach has been the regular use of insecticides to remove food sources for insectivorous birds and even distributing poison to remove potential raptor prey such as rabbits. Open water storage ponds within airports have been netted to prevent waterfowl from landing on them, but camouflage has also been developed specifically to minimise the attractiveness of large bodies of water.

2) Some airports such as Singapore's Changi play bird distress and/or raptor calls to scare birds away. A less subtle method has been the regular discharge of loud sounds generated by sonic cannon such as propane exploders. However, evidence suggests that birds soon become accustomed to these.

3) As an antithesis to the removal of food sources described above, adding chemical repellents to airport vegetation is now being used. Since 2010, New Zealand airports have been using a a locally-developed grass, which contains an endophyte fungus that reduces insect numbers and makes birds sick. This may prove to be easier to implement than natural chemical repellents imported from agribusiness, such as methyl anthranilate and anthraquinone, which require sophisticated, ongoing and locally-tailored programmes to maintain effectiveness.

4) Although it might sound high-tech, the use of wind-blown metallic streamers that simulate fire have been found to only fool birds for short periods. Likewise, the use of lasers, flare launchers and other live pyrotechnic devices serve to acclimatise local wildfowl to sudden noise and light. After all, the birds are already congregating around noisy aircraft for much of the day!

5) For airports frequented by raptors, live prey such as pigeons can serve as bait for sophisticated traps that notify staff once they have been triggered. The problem then is where to release the bird of prey so that it doesn't return to the original area.

6) The opposite of the previous method is to swamp the locality with trained predators, from dogs to raptors, in order to convince birds to nest elsewhere. The predators don't have to always be live, either: in the USA, fake coyotes have been used in wetlands to keep birds away from flight paths.

7) If all other methods fail, there are several time-consuming alternatives that could be used as a last resort. Firstly, birds can be caught and moved to regions far from airports. Naturally, this requires collaboration with wildlife experts and/or rangers. As a guaranteed solution, culling may also be allowed, although this is hardly going to endear most people to a sector that, essential though it is, has a rather poor environmental record.

One potential smart solution for civilian aviation has been developed for the Royal Netherlands Air Force, which involves constant radar monitoring of wildfowl so that pilots can adjust their take-off and landing flight paths. Apart from lack of the technology at airports, each airport would need long-term trials to determine the appropriate adjustments with regard to local bird populations and their behaviour.

From what I've learnt while researching this issue, there is probably no single solution suitable for all airports; a suite of methods is required, tailored for each one depending on the local landscape, climate and of course bird species - the latter being wily and unpredictable adversaries. Clearly, there's a long way to go if such drastic solutions as culling the birds themselves and poisoning the wider ecosystem are seen as valid options. It looks as if more research is required before the danger to both airliners and birds can be reduced, although I doubt if it could ever be completely eliminated; nature is just too unpredictable!

Spray and walk away? Why stratospheric aerosols could be saviours or destroyers

My first scientific encounters with aerosols weren't particularly good ones. In my early teens, I read that the CFC propellants used as aerosols were depleting the ozone layer. Therefore, tiny atmospheric particles had negative connotations for me from my formative years. This was further enforced by Carl Sagan and Richard Turco's 1990 book A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race, which discussed the potentially devastating effects of high-altitude aerosol's around the world following a nuclear attack. Strike two against these pesky particles!

Of course aerosols aren't just man-made. The stratospheric dust particles generated following the Chicxulub impact event 66 million years ago are known to have been instrumental in the global climate disruption that wiped out the dinosaurs and many other life forms. This would have been in addition to the thousands of years of environmental changes caused by sulfur aerosols from the Deccan Traps supervolcano. Rather more recently, the Mount Tambora volcanic eruption in 1815 led to starvation and epidemics around the world for up to three years.

Now that our civilisation is generating a rapid increase in global temperatures, numerous solutions are being researched. One of the most recent areas involves reducing the amount of solar radiation reaching the Earth's surface. Several methods have been suggested for this, but this year sees a small-scale experiment to actually test a solution, namely seeding the atmosphere with highly reflective particles in an artificial recreation of a volcanic event. The Stratospheric Controlled Perturbation Experiment (SCoPEx) is a solar geoengineering project involving Harvard University that will use a balloon to release calcium carbonate in aerosol form at about twenty kilometres above the Earth's surface, analysing the local airspace the following day to assess the effects.

This experiment is controversial for several reasons. Firstly, it doesn't lead to any reduction in greenhouse gases and particulate pollutants; if anything, by sweeping the issue under a stratospheric rug, it could allow fossil fuel corporations to maintain production levels and reduce investment in alternatives. If the recent reports by meteorologists that natural and non-intentional man-made aerosols are already mitigating global warming, then the gross effects of heat pollution must be higher than realised!

Next, this sort of minute level of testing is unlikely to pinpoint issues that operational use might generate, given the chaotic nature of atmospheric weather patterns. To date, numerous computer simulations have been run, but bearing in mind how inaccurate weather forecasting is beyond ten days, nothing can be as accurate as the real thing. Therefore at what point could a test prove that the process is effective and safe enough to be carried out on a global scale? Possibly it might require such a large scale experiment that it is both research and the actual process itself!

The duration that the aerosols remain aloft is still not completely understood, hinting that regular replenishment would be essential. In addition, could the intentionally-polluted clouds capture greater amounts of water vapour, at first holding onto and then dropping their moisture so as to cause drought followed by deluge? Clouds cannot be contained within the boundaries of the testing nation, meaning other countries could suffer these unintended side-effects.

It may be that as a back-up plan, launching reflective aerosols into the stratosphere makes sense, but surely it makes much more sense to reduce greenhouse gas emissions and increase funding of non-polluting alternatives? The main emphasis from ecologists to date has been to remove human-generated substances from the environment, not add new ones in abundance. I'm all for thinking outside the box, but I worry that the only way to test this technique at a fully effective level involves such a large scale experiment as to be beyond the point of no return. Such chemical-based debacles as ozone depletion via chlorofluorocarbons (CFCs) prove that in just a matter of decades we can make profound changes to the atmosphere - and badly effect regions furthest removed from the source itself.  So why not encourage more reducing, reusing and recycling instead?