Last week I took a visit to the university lake where I met
a Great Cormorant. His face looked like the cross between that of a dinosaur
and a gnarly troll. Given that previous description, it seems impossible for me
to like this bird, but given his crafty and wily nature, his phenomenal
resilience, and incredible hunting skills I could not help but enjoy the
company of this prehistoric animal.
I first caught sight of the cormorant at the side of a lake,
basking with his wings welcoming the sun. It is easy not to wonder why the
cormorant undertakes the task of drying his wings, but I could not help but think
this myself. As his looks would suggest, the Great grey Cormorant is one of the
most prehistoric species, along with the Shags. Unlike the more recently
evolved water bird species, the cormorants have not evolved a waxy coating on
their feathers, and so understandably will get rather wet after a hunt for his
fish or whatever meal is available. After becoming sodden from a hopefully successful
attempt to catch dinner, the cormorant will stand on a perch for an hour if
needed to dry off any water that may not be shaken off. While this
characteristic is reasonably interesting, the wing drying behavioural quirk
provided scientists with the ability to carry out an experiment revealing something
rather more intriguing.
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One of the Coromorant standing minding his own business |
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A cormorant looking back very disapprovingly at me after folding back his wings, and ceasing
to dry his feathers |
Recent research has been
undertaken to study the migration behaviours of Roach fish. Through use of the
cormorant feeding behaviour, evidence has been gathered to demonstrate the
reasoning behind migrations. Once a cormorant has caught a fish, he will
regurgitate spit balls at the perch on which he is drying his feathers on. If a
fish has been pit tagged (a form of microchip-like identification), all morphometric measurements can be taken of that
fish, and so we can understand what size fishes are being eaten by
the cormorant. It was found that fish spending more time outside a lake would
be less likely to be eaten by the cormorants, but will also be less likely to
find plentiful food. In addition to this, it was found that the bigger fish
were more likely to get caught. Using this information, and the information of
when the fish left the lake to migrate, they found that when the risk of being
predated outweighed the food benefit provided by a lake over another stream,
the fish would leave the lake. Bigger fish were more likely to leave the lake,
and especially so when predation pressures were high and less food was
available in the lake.
While the cormorant is currently
causing great concerns with regards to impact on current biodiversity, given
past distributions I cannot help but admire the resilience of this species. Historically,
cormorants were regarded as an irritating competitor for fish by fishermen, and
so were nearly hunted to extinction. Since, the Great Cormorant has escalated
in numbers to the 1.2 million individuals in Europe today. The Great Cormorant is
now thriving in the UK, and now the species is predicted to cause incredible
changes in our aquatic and terrestrial ecosystems. There are great concerns over
the impacts that cormorants may have on ecosystems, with relocation of matter and
microbial agents between ecosystems, and the possible food web modifications
that may follow the cormorant’s population growth. It is true that in the
future we may need to control cormorant populations, however it is still
fantastic to see such a prehistoric creature on our doorstep, and I thoroughly
enjoyed admiring the bird in the sun all the same.
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This isn't much to do with the blog, however I did think the gulls looked
brilliant sitting in a line along the concrete posts |