nominate Lesser Black-backed Gull (L. f. fuscus)

(last update: 23-1-2011)

Images presented in this section are from Israel, where nominate fuscus is a regular visitor.

Primary moult

The moult sequence in nominate Lesser Black-backed Gull Larus fuscus fuscus was already described by Stresemann & Stresemann in 1966 in Journal für Ornithologie. They described a periodische Staffelmauser, a step-wise moult. Normally, large white-headed gulls in Europe start replacement of the remiges during the breeding season and finish this moult in autumn, prior to their migration.

Stresemann & Stresemann described fuscus as an exception as it doesn't start the remiges moult before arriving at the wintering grounds in Africa and the Mediterranean. For a long-distance migrant like fuscus, this seems to be a suitable strategy. This pattern can also be found in long-distance migrants like Terns (Sternidae).

Stresemann & Stresemann examined skin collections and failed to find any adult L. f. fuscus originating from the breeding or autumn migratory range that was in active primary moult. Therefore they presumed the entire moult stage takes place on the wintering grounds. Adult birds on migration had been collected (Rossitten Bird Observatory, Russia) and these birds confirmed the theses: they must have suspended moult, as Heinroth (1928, Die Vögel Mitteleuropas) concluded: adult fuscus doesn't show active primary moult on migration. They either suspend moult or do not commence moult before arrival on the wintering grounds.

However, there are a few museum skins that do show adult fuscus in primary moult: the Zoological Museum of Helsinki (not visited by the Stresemanns in 1966) has 21 skins of summer / early autumn birds: 8 are showing moult in the primaries. The museums of Copenhagen and Tring have 10 skins in collecting from the same period: one is showing active primary moult.

The last decades, the general idea about the renewal of the primaries in adult fuscus has been changed slightly. Field research showed that a small majority (up to 60% in southern Sweden) of the adult fuscus have started to replace the inner one or two primaries on the breeding ground by late August. This primary moult is suspended until arrival at the tropical wintering grounds. Fuscus complete their primary moult in February and March, just before leaving again to the breeding grounds in Scandinavia and northern Russia. By March, the inner primaries may in some birds included in the primary moult, in a second wave. This seems to be a common feature in especially sub-adult birds.

As soon as birds arrive in S Europe and Africa, primary moult is started (again) and a complete moult takes place, normally in the ordinary sequence as it is found in many large white-headed gull taxa in N Europe. The table below illustrate the moult scores for Israelian birds, photographed by Amir Ben Dov.

Table adult September

Table showing old and new primaries in adult fuscus in September; data for Israel (2008-2011).

P6 new = P6 longest new primary; it exceeds the previous primary in length (so P6 new / fully grown, only from the moment when it is longer than P5).

Amir Ben Dov visited Ashdod on 17.9.2010. About 150 - 200 gulls were present, with only 3 ringed adults from Finland. Weather did not allow appropriate scores in the field, but the general idea was that most adult fuscus had dropped P1-P2. One bird missed P1-P2, but had P3-P4 growing at about 30% of the final length (irragular moult strategy). There were also a few birds which had not started the complete moult yet (P1-P10 present).