Peter Shute wrote:
"The types of noise may have different effects on different species too.
The steady roar of a jet is very different to the sharp clatter of a
helicopter, for example. Some noise regulations even take the extra
annoyance of "impulsive" noises into account by deeming them to be several
decibels higher than the measured levels."
I agree. I had to review the potential disturbance impacts of helicopters on
waterbird and shorebird populations earlier this year. Disturbances to birds
by helicopters have been well studied (overseas, not so much in Australia)
and documented in the scientific literature.
Again, there are species-specific differences in responses to helicopters,
but it is generally accepted that helicopters operating on or close to the
ground have larger disturbance impacts on birds than most passenger planes.
These disturbances are greatest when helicopters are hovering between
100-350 m above bird habitats, but are reduced significantly when
helicopters are flying at altitudes of 450 m or more.
In the case of a hovering helicopter, some birds are probably reacting to
both noise (both impulsive and loud sounds) and the sight of a "potential
aerial predator".
Stephen Ambrose
Ryde, NSW
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