Spotlighting

I've been doing a bit of underwater photography lately, and  know
that in water, reds and infrareds are filtered out the deeper you go down.

From an evolutionary standpoint, aquatic
animals have developed senses in the ultravoilet range and have little
need to develop senses in the infrared range.

I'd think that due to the suggested
common ancestry of all land animals from the sea , that the infrared spectrum
would be less developed than the ultravoilet spectrum, and hence red light
would disturb all land animals less.  Especially nocturnal animals.

My two cents worth is, never shine a
direct beam into the eyes of any animal anyway...use the outer cone of
the beam.

Andrew Taylor <>
Sent by:

23/09/2009 02:28 PM

Please respond to

To
cc
Subject	Re: [Birding-Aus] Spotlighting

If you are interested in with spotlighting at lower
illumination levels,
some LED torches like my my iTP c8  can be varied continuously:
http://www.torchworld.com.au/catalog/index.php?main_page=product_info&cPath=99&products_id=552
and some allow their output to be to set at several levels like this one
(on my wishlist) based on the new Cree MC-E LEDs:
http://www.torchworld.com.au/catalog/index.php?main_page=product_info&cPath=96&products_id=532

Red light has been used for ~50 years to observe mammals because it
supposedly reduces disturbance - and presumably it does but a quick search
didn't turn up any hard data actually  establishing this.  There
is one
group where it should be effective, some turtle nesting areas permit
only torches with red filters and judging by the visual pigments reported
for some turtle species, they are likely insensitive to red light.

Generalizing between species looks dangerous. Just within the primates
you
find trichromats like us, dichromats with only 2 channel colour vision
(common in mammals) and even monochromats.  In some squirrel monkey
species  males are dichromats and females can be either dichromats
or
trichromats.  If there are fundamental variation in vision, you wouldn't
expect physical effects from being spotlighted to be consistent between
species.

And Alan Gillanders make a good point that apart from any physical
effects, behaviour responses depend heavily on context.  Just as in
wetlands where hunting occurs, approaching within  several hundred
metres can ducks to flee whereas elsehwere much closer approach will
cause little response.

Andrew
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birding-aus.blogspot.com

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