Hi all,
As Mike Carter has already expressed, this months BA Victorian Port
Fairy Pelagic was interesting for the lack of birds seen (with a dearth
of pelagic species).
The conditions were warm and humid, and for most of the day the water
was very flat and glassy. For the first time that I have experienced,
NO (zero) birds responded to the shark liver berley.
This general lack of response even occurred when we stopped near flocks
of albatross, shearwater and petrel resting on the water (despite
tossing burley with in a bills reach!) These birds may have been
satiated on food scraps from a passing trawler, however the more likely
cause for their lethargy is that in the windless conditions the energy
expenditure in feeding did not match the energy return.
For example, to fly albatross utilise the friction on the water
surface, whereupon the air pressure above the wing is less than the air
pressure under the wing (known as the Bernoulli principle), which
pushes the bird up in the sky. The utilisation of wind and waves means
almost no muscular exertion save the infinitesimal effort required for
steering and balancing. When there is no wind and no friction the
albatross actually have to flap their wings!
This raises an interesting question: what sparks the bird?s behaviour -
from lethargy in windless conditions to wanting to eat in windy
conditions. How do they know to start feeding? Avoiding the temptation
for anthropomorphism, is this a learned cultural experience or is there
some biological spark?
Apart from stifling the birds, the calm conditions meant the water
surface was glassy flat, which also meant we could easily see signs of
life in (or under) the water. During the trip we saw at least one Sperm
Whale, a Blue Shark, large numbers of Common Dolphin, as well as large
numbers of Australian Fur Seal. (There was also an Elephant Seal on
Lady Julia Percy Island.)
Also putting the pelagic to one side, there were a few interesting
birds on Griffith?s Island (Port Fairy). These included a single
Sanderling, a pair of Hooded Plover, several flocks of Ruddy Turnstone,
and a single Common Sandpiper.
Cheers,
Tim
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