Variation in primary moult in Lesser Black-backed Gulls in January

From literature 1 it is known that adult Lesser Black-backed Gulls from northern origin (Larus fuscus intermedius and L.f. fuscus) can still be moulting their outer primaries well into January and February or even March, while Western Lesser Black-backed Gulls (L. f. graellsii) will typically have completed their primary moult in December.

During my visit to Morocco last January, it was interesting to come across various adults and sub-adults that were still in the process of growing the outer primaries. Most though had completed their primary moult.

I will show some examples here.

Gulls of Europe, Asia and North America – Klaus Malling Olsen and Hans Larsson

Adults with primary moult

Individuals with outer and inner primary moult

Interestingly, two individuals showed moult in the outer primaries (P10 not fully grown) as well as in the inner primaries (P1 and P2 missing).

Adult Lesser Black-backed Gulls are known to arrive in the breeding colony with new inner primaries (see this link on Gull Research and this link as well). It makes sense therefore that these are replaced at the wintering grounds. What I find interesting though is that this takes place early January and while the outer primary is still growing (so effectively Staffelmauser moult: two different moult cycles active simultaneously). It is probably done to make sure that the full process is complete by the time they need to migrate again. Also, the inner 2 primaries are the smallest and take the least energy to replace. Highly nutritious food was also available (I saw these at the Anza fish factory) so that may also come into play.

Individual #1

ind-1-20170104-1

ind-1-20170104-2

Individual #2

ind-2-20170105-1

ind-2-20170105-2

Black NH5L, Nordic Lesser Black-backed Gull (intermedius)

6th-calendar year from Norway, P9 almost complete, P10 half grown.
Primary moult score 46 (5555555542).

n-nh5l-20170104-2

n-nh5l-20170104-1

n-jh5l-20170113

Black J130E, Nordic Lesser Black-backed Gull (intermedius)

5th-calendar year from Norway, all primaries fully grown.
Primary moult score: 50 (5555555555).

n-j130e-20170109-1

n-j130e-20170109-2

Blue 8W, Western Lesser Black-backed Gull (graellsii, Dutch intergrade)

Older than 11th-calendar year female from Belgium, P10 not fully grown yet.
Primary moult score: 49 (5555555554).

b-8w-20170109

b-8w-20170109-2

Unringed individuals

Individual #1

P10 almost fully grown. Primary moult score: 49 (5555555554).

graellsii-20170113-1

Individual #2

P10 almost fully grown. Also note the missing tail.
Primary moult score: 49 (5555555554).

lbbg-no-tail-20170105-1

Individual #3

P10 almost fully grown. Primary moult score: 49 (5555555554).

graellsii-20170109-1

Individual #4

P9 almost fully grown, P10 half grown. Primary moult score: 47 (5555555543).

graellsii-20170109-2

Individual #5

P10 almost fully grown. Primary moult score: 49 (5555555554).

graellsii-20170109-3

Sub-adults with primary moult

Blue VZ6Y

Very advanced 2nd winter / 3rd-calendar year from Denmark. P1 to P5 fully grown, P6 3/4 grown, P7 missing, P8 to P10 old.
Primary moult score: 30 (5555541000).

For more images, see 3CY Lesser Black-backed Gull Blue VZ6Y with active primary moult in January – 20170105.

B-VZ6Y-20170105-1

Adults with no primary moult

Green KADD, Western Lesser Black-backed Gull (graellsii, Dutch intergrade)

8th-calendar year from the Netherlands, all primaries fully grown.
Primary moult score: 50 (5555555555).

g-kadd-20170104-1

Yellow 8V:W, Western Lesser Black-backed Gull (graellsii)

Older than 7th-calendar year male from the UK, all primaries fully grown.
Primary moult score: 50 (5555555555).

y-8vw-20170109-1

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