Sunday 19 February 2023

Vega Gull moult timing abnormality

I saw this gull at day's end, the very last light, while looking for a Canvasback to round off a successful twitch for Little Gull on Feb 1.

The Vega is missing four inner primaries on each wing, the innermost secondaries and a few primary coverts. Is it six months early or six months late? The first thought must be that a health issue resulted in suspension of moult. However, if that were the case the outer primaries would be extremely distressed by now, whereas there’s no sign of any wear at all. So, it would appear the bird has commenced moult six months early! Either that or is undergoing an ‘additional’ moult. The possibility that had had spent some serious vagrancy time in the southern hemisphere and had adopted their perverse moult habits before returning north would seem fanciful at best. Needless to say, this is a stage of moult not normally witnessed in Japan.

In the flight images there is a suggestion of pigment deficiency in the flight feathers; if it were a paint job, I’d say the grey doesn’t look evenly applied. However, it’s difficult to rule out photographic artefact under the low light conditions. Even if there is a pigmentation issue, it may indicate some underlying problem that has resulted in this abnormal moult timing. There are two other points to add: firstly that it looks a young adult because of the touch of black in the gonys, but the moult would have synchronized with adult by this age, and secondly that p5 has limited sub-terminal black, unusual but not unheard of for Vega.

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