Sunday, 5 December 2010

'Leggy' Herring Gull, Musselburgh, 18 November 2010

Any white-headed and long-legged immature large gull is worth more than a quick glance in Scotland, with both Yellow-legged Gull and Caspian Gull being such rarities north of the border.

This first-winter (1CY) bird initially looked very leggy next to a more compact adult Herring Gull at the edge of the Oystercatcher roost. As I phonescoped some record shots of it seemed to be showing clearly longer legs, particularly above the 'knee' (actually the ankle, of course).

While it jumped out at me as a candidate for one of the southern species, the lack of moult of any of the juvenile feathers in the coverts or tertials, combined with the pattern of fringing on the tertials soon left me with little doubt that this was a young Herring Gull.

The bird was restless, moving around, behaving aggressively towards other birds and attempting to feed in the water flowing across the ash lagoon. The more I looked, it became clear that the legs were not really any longer than some of the other birds present. In fact, I now think that the apparent leg length is the result of the lack of any decent belly or belly feathering on this bird – no wonder it was eagerly trying to feed.

Here it is on the right hand side of the foreground. Compare its leg length to the similar bird in the background on the right.

After a few more minutes I noticed the bird take flight and managed to grab a few shots.

The predominantly dark tail, pale inner-primary window in the wings and strong contrast of the dark subterminal bar along the secondaries with the pale notched coverts gave further confirmation of the bird as a Herring Gull.

What was obvious in flight was the fact that the bird is missing primary feathers in both wings. This left me with the feeling that I had been looking at a moulting second calendar year bird (i.e. second winter) all along, which could explain a white-headed appearance. The photographs reveal that the missing primaries are quite unevenly positioned – so maybe a result of damage or injury – as well as the fact that the inner primaries do not look like newly grown second generation feathers.

So, an interesting exercise for me in examining yet another odd-looking Herring Gull, but a sense of unease for the chances of survival for what may be an undernourished and injured bird.

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