Moerdijk Field Research 2005-2006

(last update: 14 August 2010)
coordinators: 
Roland-Jan Buijs
Theo Muusse
Mars Muusse

Home

Introduction
Methods
Age, origin & sex
Retrapped Birds
Upperparts Greytone
Black on Primary Coverts
Black on Primaries
P10 and P9 Patterns
P5 Pattern
Red & Black on Bill
Iris & Orbital Ring
Primary Moult
Discussion
References

 Larus argentatus argenteus & Larus fuscus graellsii - Moerdijk, the Netherlands

Age of sample birds, origin & sex

Breeding birds are not necessarily fully mature adults, as both Herring and Lesser Black-backed Gull may breed as sub-adults. Chabrzyk & Coulson (1976) found that 14% of Herring Gulls start breeding as 4cy birds (also see Drost et al., 1961). In the Herring Gull we used black on the primary coverts as a feature to separate between fully mature birds and sub-adults (see thumbnails). In the results, we will distinguish between sub-adult and adult birds (showing clean grey primary coverts, see thumbnails) when results need separation for age.

Fully mature Lesser-black-backed Gulls may still show obvious black markings on the primary coverts (personal observations based on ringed birds). We have illustrated all greater primary wing coverts of known-age birds HERE. We classified sub-adults as obviously immature birds, considered 4cy and 5cy, with extensive brown-black on the primary coverts. By doing so, we may have excluded delayed 6cy or older birds and included advanced 4cy or 5cy birds. However, in the absence of any other safe criterion, primary covert markings were considered the most appropriate way to distinguish full adult from sub-adult birds (see plate 3). Sixty-two Lesser Black-backed Gulls were scored ‘sub-adult’: 43 males and 18 females. The sex-ratio for the total sample is reverse: 443 males and 515 females.

Based on ring recoveries, the first breeding birds at Moerdijk (early 1980s) probably originated from the vast colonies at Maasvlakte and Dintelhaven (51.57N 04.01E). In recent years we have also found birds which were born in the recently established colony of Zeebrugge, Belgium (51.21N 03.11E). Ring readings show that nowadays the Moerdijk colony mainly hosts locally-reared birds.

In 2005-2006 we ringed and measured 315 breeding Herring Gulls (165 males and 137 females, 13 birds not sexed) and 1038 Lesser Black-backed Gulls (460 males and 535 females, 43 birds not sexed). Wingspan in the Herring Gull population ranges from 385 – 465 (average 427) and ranges from 385 – 462 (average 426) in Lesser Black-backed Gulls (table 1). We trapped 113 birds of known age (35 Herring Gulls and 77 Lesser Black-backed Gulls). Known age varied from 4cy to 19cy. The oldest known bird in our sample is Dutch HG mS0, born in 1987 (i.e. 19 CY) and caught in the Moerdijk colony in 2005.


range average SD
HG ♂ 413 - 465 437 9.3
HG ♀ 385 - 430 415 7.8
LBBG ♂ 410 - 462 438 8.9
LBBG ♀ 385 - 435 415 8.2

Table 1: Wingspan (in mm) in Herring Gull and Lesser Black-backed Gull.

 Lesser Black-backed Gulls with extensive black on the primary coverts: sub-adults Herring Gulls with black on the primary coverts: sub-adults
Lesser Black-backed Gull L.f. graellsii sub-adult 67, 05 May 2005. Herring Gull L.a. argenteus 4cy-5cy 6T, 21 May 2005 & 09 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 72, 05 May 2005. Herring Gull L.a. argenteus 4cy E4, 02 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 73, 05 May 2005. Herring Gull L.a. argenteus 5cy-6cy 13, 05 May 2005 & 09 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult HV, 16 May 2005. Herring Gull L.a. argenteus 5cy HK, 04 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 5E, 08 May 2006. Herring Gull L.a. argenteus 5cy J2, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 5P, 08 May 2006. Herring Gull L.a. argenteus 6cy J7, 09 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 5X, 08 May 2006. Herring Gull L.a. argenteus 7cy K2, 09 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 7A, 09 May 2006. Herring Gulls without black on the primary coverts: adults
Lesser Black-backed Gull L.f. graellsii sub-adult 7K, 09 May 2006. Herring Gull L.a. argenteus 5cy HT, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 7N, 09 May 2006. Herring Gull L.a. argenteus 5cy NU, 23 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 7X, 09 May 2006. Herring Gull L.a. argenteus 6cy 3T, 14 May 2005.
Lesser Black-backed Gull L.f. graellsii sub-adult 20, 06 May 2006. Herring Gull L.a. argenteus 6cy K4, 09 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 32, 06 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 40, 08 May 2006. Lesser Black-backed Gulls with extensive black on the primary coverts: sub-adults
Lesser Black-backed Gull L.f. graellsii sub-adult CV, 06 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult EV, 04 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult E0, 14 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult HS, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult HZ, 14 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult HY, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult JZ, 14 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult JP, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult KJ, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult K3, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult LE, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult K5, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult S2, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult K9, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult S7, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult KZ, 05 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult S9, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult LH, 13 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult SX, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult LP, 13 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult SZ, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult LS, 13 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult TL, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult M0, 13 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult TP, 21 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult MC, 13 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 1P, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult N6, 15 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 1S, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult NA, 13 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 1T, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult PB, 16 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 12, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult PK, 16 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult 14, 16 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult PY, 16 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult A9, 02 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult PZ, 16 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult AE, 02 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult S6, 04 June 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult AY, 02 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult S7, 04 June 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult BA, 02 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult S8, 04 June 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult BW, 03 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult SA, 23 May 2006.
Lesser Black-backed Gull L.f. graellsii sub-adult CV, 04 May 2006. Lesser Black-backed Gull L.f. graellsii sub-adult TR, 04 June 2006.
We have illustrated all greater primary wing coverts of known-age birds HERE.