On Tue, 14 May 2002, Simon Mustoe wrote:
> Another example of a potentially clandestine impact would be electromagnetic
> radiation. Take Basslink for example. The impacts of this on marine mammals
> and fish, including sharks and rays, is considered quite potentially
> damaging. But what of the effects on migrant birds crossing the Bass Strait.
> And this effect is not only confined to the cable. There are radar stations
> and other microwave producing structures along our coastlines.
>
> There is a fascinating paper by Wiltschko et al. on these effects on migrant
> Tasmanian Silvereyes. Much in the style of the original bird migration
> studies using caged birds in planetariums etc., the authors took spring
> migrating Silvereyes and subjected them to a strong magnetic pulse. This
> resulted in a significant deflection towards the east for 4 days and it took
> 10 days for birds to resume normal behaviour.
The paper is certainly interesting but direct conservation implications
aren't obvious. The magnetic field used was large - a similar strength
to that inside an operating MRI machine. Fortunately for Silvereyes
(and people with pacemakers), accidental encounters with fields of this
strength are unlikely. I don't think many birds are going to have their
magnetic perception (temporarily) damaged by encounters with artificial
magnetic fields.
We've known for a while that birds may use magnetic fields for navigation.
Wiltschko has been researching this area since the 1960s. Artifical
magnetic fields may alter the magnetic "map" birds use. Fortunately,
the strength of magnetic fields declines very quickly with distance from
the source, which should greatly limit any such effects.
Basslink perturbations of the magnetic field and hence bird navigation
should be limited to its immediate vicinity - say within ~100m of the
cable. Its hard to see why this perturbation should have a significant
impact when there is existing natural variation in the magnetic field
from geological causes of greater magnitude.
The impact, if any, of the electric field from Basslink on marine animals
with sensitive electro-receptors, such as some sharks is harder to assess,
but its drawing a long bow to say its "quite potentially damaging".
When considering such tenuous negative possibilities, you shouldn't forget
the positives. Interstate connections such as Basslink, can increase the
efficiency of electricity generation and hence have positive environmental
impacts such as reduction in carbon emissions.
I don't know of any physically plausible impacts on migrating birds from
microwave transmitters other than in the immediate proximity (say within
~10m) of the transmitter. As cell phone users are only millimetres
from a microwave transmitter for extended periods, there has been quite
a bit of research on the biological effects of microwave radiation.
Andrew Taylor
Birding-Aus is on the Web at
www.shc.melb.catholic.edu.au/home/birding/index.html
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