Hi Belinda,
There are many reasons why there are bird strikes.
First, there may be visibility problems when both birds and planes are in
flight, as a result of clouds, fog, rain, snow, dust in the atmosphere or
other inclement weather. It would be interesting to know how well birds
(particularly migratory birds in full flight) can hear the sounds of
approaching aircraft because I imagine that the sound of air-streams passing
over, under and around the bird's body would be quite loud. I also wonder if
birds that are resident at airfields (particularly the larger airports) have
impaired hearing as a result of being subjected constantly to the sounds of
jet engines.
Secondly, although there are bird strikes at high altitudes, most do occur
at lower altitudes when planes are landing or taking off from air-strips.
Airports need a flat terrain, so they are usually located on coastal plains,
flood plains or plateaus. These locations usually attract birds in high
densities. Moreover, aerodromes usually have large expanses of lawned or
grassy areas around the runway, which attract ground-foraging birds (e.g.
galahs, corellas, masked lapwings, magpies, corvids), aerial predators (e.g.
raptors). Rainwater also tends to pool on the sides of runways and in
depressions within grassed areas and they tend to attract wading birds (e.g.
herons, egrets, lapwings, some wader species). Surrounding land-uses also
attract high bird densities, e.g. rubbish tips, free-range farms and beaches
can attract Silver Gulls, White Ibis, crows and ravens in high densities.
For instance, large numbers of Silver Gulls pass through air-space above
Adelaide Airport, because on one side of the airport is the coastline and on
the other side there is a rubbish tip (both separated by a distance of about
10 km). Many airports that are located on floodplains or coastal plains are
also located close to large colonial roosts of wetland birds or seabirds.
Additionally, many airports are located with migratory pathways of birds and
bats. The point is, the higher the density of birds (and planes), the
greater the risk of bird strikes.
Thirdly, resident and experienced (older) birds become habituated to the
presence of aircraft in their region and I believe that they learn how to
avoid them. I suspect that many bird strikes involve birds that are either
young and naïve (they haven't yet learned how to avoid aircraft) and those
who are passing through the air-space of airports on migration, dispersing
to new areas or moving nomadically (and hence not as familiar with the
pattern of aircraft movements). We see this to a large extent in our road
kills - it's usually the younger, less experienced birds, that are run down
by vehicles.
Fourthly, the suction power of a jet engine is extremely powerful, so birds
in flight may see a plane and try to avoid striking it, but it is too late
because it is already caught in the engine's jet-stream. Even birds that are
foraging in grassed areas along the sides of runways are known to have been
sucked into jet engines as planes taxi along the runway. There's also not
much of an opportunity to avoid an airborne plane approaching you at 300-500
km/hr, especially if you are also flying towards it.
Stephen Ambrose
Ryde, NSW
-----Original Message-----
From:
On Behalf Of Gemfyre
Sent: Saturday, 20 June 2009 11:20 PM
To: Rob Geraghty; 'Birding-Aus (Forum)'
Subject: Canada Goose Cull
One wonders why the birds don't take the evasive action. Surely a loud,
large plane bearing down is hard to miss, and birds have considerably better
maneuverability than a plane.
Belinda Forbes
Stirling W.A.
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