Monday, 24 May 2010

Fishy business

It is good to be out on the water, sat in a large inflatable and at eye level with the dashing forms of Swallows and occasional passing terns. We are here to ring nestling Cormorants, a colony of which breeds in the trees that fringe Abberton Reservoir. There are five of us in all, split between the two boats which we paddle slowly around the reservoir, assessing the stage of each nest in turn before determining which ones should be approached for ringing.
Cormorant ringing in a previous year, before we had boats!

These inland breeding Cormorants are part of an expanding inland population, a relatively recent development set against a longer history where virtually all of our Cormorants were coastal in their habits. Part of the reason for this change is the establishment of colonies of the continental race, known as sinensis. This race originates from breeding colonies in France and the Netherlands where it breeds almost exclusively alongside inland freshwaters. Unlike our own race, known as carbo, the continental birds are migratory in their habits and their arrival here appears to have had an influence on the establishment of these inland breeding colonies. The colony at Abberton started with just nine pairs in 1981, growing rapidly to a peak of 551 pairs in 1996, since when numbers have fallen; we recorded just 160 pairs during our visit.

Ringing Cormorants is hard work. Not only do you have to paddle around the reservoir but you also have to spend a lot of time in the water, wading up to the partially submerged trees used for breeding, before erecting a ladder and climbing up to the nest. Then there are the birds themselves. Any adults in the tree, of which there are usually a few, retreat out onto the water to form a scattered raft of sleek black shapes with alert, periscope heads watching our activities. The chicks are relaxed in the hand but will invariably relieve themselves all over you and, occasionally, bring up a lump of partially digested fish. It is smelly but important work. Each of the chicks receives both a standard metal ring and special colour ring, the latter marked with three large digits that can be read at a distance using binoculars. These colour rings enable researchers to collect far more information on the movements of the birds than they would otherwise be able to.

Our visit to each small cluster of nests is brief, just 10 or 15 minutes on a warm day like this, allowing the adult birds to return to feed their chicks with minimal disturbance on our part. I know that Cormorants are not the most popular of birds with fishermen but there is something truly endearing when you encounter them as soft-feathered youngsters.

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