Hi,
Birds I understand can see polarized light. There is something on the web
about albatrosses having two foveas, which are the area of the eye used for
acute sight perception - biologists out there may understand this. What I do
know is that when you drip oil off the back of a boat, birds will go for it
even if there is no detectable food and their ability to find patches of
prey on the sea is as much determined by their ability to see oil, in my
opinion, as it is on their ability to smell it.
It is quite possible that birds live in this amazingly colourful world where
they can see rainbow patterns on the surface of the ocean which we are blind
to and indicate the presence of food. After all, most dead ocean dwelling
beasts are amazingly oily.
On a pelagic recently we had very rough weather and waves were crashing over
the stern. Some shark liver berley was still in the berley tray and it
gradually dissolved until occasionally all that would enter the water was a
drip of oily saltwater off the corner of the tray. You could see it happen
so just after a wave hit the side of the vessel and spray hit the tray, the
material would wash towards the corner and a single drip would form then
drop into the ocean. All it took was one drip to hit the white-water off the
stern and a dozen wedge-tailed shearwaters would dive into it. It was
imperceptible to me until about 100m behind the vessel when the oil had
spread to form a round and very slight calm patch.
This was not visible directly behind the boat simply because the white-water
was far too violent and yet the birds were able to detect it seconds after a
single drip.
I agree, the results of the recent studies merely prove that putting oil in
the water causes birds to follow the trail, which is fine if there is some
wind or the vessel is moving and as long as there is no 'food' evident in
the oil.
Cheers,
Simon.
-----Original Message-----
From:
On Behalf Of Roger Giller
Sent: Thursday, 20 July 2006 11:47 AM
To: Birding-Aus
Subject: Shark Liver Oil as a Seabird Deterent
Hi All,
I know this was the subject of a previous thread but I was on digest mail
delivery at the time and could not add my two penneth-worth. Now back on
individual delivery and waited a while but no more messages on the thread so
I resurrected it.
In my earlier, pre-birding, days I used do a reasonable amount of off-shore
fishing from small boats. One technique we used was to berley with cut up
pilchards and small pieces of tuna etc. We were often plagued by "Mutton
Birds" which, when we thought we knew something about birds and wanted to
show off, we used to call Shearwaters. For a time we were not even aware
that there are different species of Shearwaters! How things have changed.
Anyhow, the birds would cluster around the back of the boat, stealing the
berley before it had time to sink and also chasing our baits with a very
real risk of being hooked. Our solution was to set up a slow drip of tuna
oil to create a slick behind the boat. We observed that most of the birds
would not alight on the water in the slick and any that did would swim out
of it and sit on the water preening themselves vigorously. It was our belief
that the oil, even though in a very small quantity, was enough to upset the
birds "floatability".
Perhaps it is the "oiliness" of the shark liver oil and not the shark odour
that keeps the birds away.
Roger Giller
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