The industrial complex Moerdijk in the Netherlands holds a mixed colony of Herring and Lesser Black-backed Gulls. Colonisation of Moerdijk started in the early 1980s. By 2006, an estimated 650 pairs of Herring Gulls and 2900 pairs of Lesser Black-backed Gulls bred in the colony. In 2005, 434 Lesser Black-backed Gulls were colour ringed at Moerdijk, with 604 ringed in 2006.
Some Lesser Black-backed Gulls in our sample showed arrested moult, as described by Stewart (2006) for British birds. We found 13 birds with P1 renewed (e.g. LBBG oCJ) and four birds with P1-P2 renewed (e.g. bird oCH). These individuals illustrate that Dutch birds occasionally moult inner primaries on the wintering grounds. None of these birds was in active moult at the time it was caught on the nest.
Another group of birds showed inner primaries that are obviously older than the outer primaries. In these birds moult was apparently arrested (e.g. to migrate south in the autumn) and continued much later, leaving a distinct difference in feather wear visible in the wing. We found five birds with P1 obviously older than P2-P10 (e.g. LBBG oET) and seven birds with P1-P2 much older than P3-P10 (e.g. bird oJX). These 12 birds match the moult strategy described for adult nominate fuscus (Jonsson, 1998). Further studies are needed to determine whether moult pattern is an individual, population or sub-species trait and, hence, the extent to which it can be used in identification.
P1 replaced recently:
1. Lesser Black-backed Gull L.f. graellsii 12cy yellowAF, 02 May 2006. P1 new & P2 old, PMS value = 5.
2. Lesser Black-backed Gull L.f. graellsii yellowB7, 02 May 2006. P1 new & P2 old, PMS value = 5.
3. Lesser Black-backed Gull L.f. graellsii orangeCJ, 06 May 2005. P1 new & P2 old, PMS value = 5.
4. Lesser Black-backed Gull L.f. graellsii 9cy yellowNL, 13 May 2006. P1 new & P2 old, PMS value = 5.
5. Lesser Black-backed Gull L.f. graellsii yellowL1, 13 May 2006. P1 new & P2 old, PMS value = 5.
6. Lesser Black-backed Gull L.f. graellsii orangeTJ, 21 May 2005. P1 new & P2 old, PMS value = 5
P1-P2 replaced recently:
7. Lesser Black-backed Gull L.f. graellsii orangeCH, 06 May 2005. P1-P2 new & P3 old, PMS value = 10.
8. Lesser Black-backed Gull L.f. graellsii orangeEZ, 14 May 2005. P1-P2 new & P3 old, PMS value = 10.
9. Lesser Black-backed Gull L.f. graellsii orangeL6, 16 May 2005. P1-P2 new & P3 old, PMS value = 10.
Example birds with old inner primaries:
10. Lesser Black-backed Gull L.f. graellsii yellowM9, 13 May 2006. P1 missing & P2 very old, PMS value = 1.
11. Lesser Black-backed Gull L.f. graellsii yellowJS, 05 May 2006. P1 growing & P2 very old, PMS value = 2.
12. Lesser Black-backed Gull L.f. graellsii yellowCJ, 04 May 2006. P1 old, PMS value = 0.
13. Lesser Black-backed Gull L.f. graellsii orangeET, 06 May 2005. P1 old, PMS value = 0.
14. Lesser Black-backed Gull L.f. graellsii orange78, 09 May 2006. P1-P2 old, PMS value = 0.
15. Lesser Black-backed Gull L.f. graellsii orangeLW, 16 May 2006. P1-P2 old, PMS value = 0.
16. Lesser Black-backed Gull L.f. graellsii yellowMT, 13 May 2006. P1 old, PMS value = 0.
