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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