The nominate race of European Herring Gull Larus argentatus argentatus occurs in the roost at Draycote Water from late autumn to early spring with large numbers present throughout the mid-winter. In 2016 two adults summered providing us with an opportunity to study them through the period when they are usually absent.

Nominate European Herring Gulls wintering in the UK are generally considered to be from the northern part of the range. Variation within L.a.argentatus is clinal with birds averaging larger and darker across the range from south to north. The photo below shows that this individual photographed on 18/08/16 is only a shade paler than the Yellow-legged Gull in the same frame.

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Ad. European Herring Gull, L.a.argentatus with Ad. Yellow-legged Gull Draycote Water, 18/08/16.

The bird also shows a restricted amount of black in the primaries. Whilst the primary pattern of European Herring Gull is variable L.a.argentatus typically show less black in the primaries than L.a.argeteus and the absence of black in the newly grown P5, long white tip to P10 and large white mirror in P9 are typical of northern L.a.argentatus but not diagnostic.  Whilst the bird thus shows several features associated with northern Scandinavian L.a.argentatus it is impossible to determine its natal origin with certainty.

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Ad. European Herring Gull, L.a.argentatus, Draycote Water, 18/08/16.

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Ad. European Herring Gull, L.a.argentatus, Draycote Water, 18/08/16.

Primary moult in adult European Herring Gull commences in May and is completed by December. Northern populations of L.a.argentatus are often said to complete the moult a few weeks later than those breeding to the south. Malling Olsen gives L.a.argentatus from southern Scandinavia as moulting P 5-6 in mid-August. A Finnish bird documented here http://www.gull-research.org/hg/hg5cy/adaug07.htm has yet to drop P7 by 09/08. The bird documented here had already dropped the old P 7 and begun regrowing P6 by 18/08/16

It can be seen that the heavily abraded tail has yet to commence moult which is consistent with the timing for tail moult given by Malling Olsen of Aug. – Oct. Head streaking, which occurs from August onwards, is apparent, particularly around the eye, though not extensive.

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Ad. European Herring Gull, L.a.argentatus, Draycote Water, 18/08/16.

I am unsure how unusual, or otherwise, this moult progression is.  If the moult is significantly advanced it seems likely to be a result of the bird summering outside of the usual range. Perhaps the moult timing was controlled by day length and thus a function of the southerly latitude at which the bird spent the summer.   An alternative explanation may be that breeding birds undergo a slower moult as energy is devoted to reproduction and the rearing of chicks.