Thursday, 25 February 2016

The Crafty Cormorant

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.
One of the Coromorant standing minding his own business

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.



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

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