Moerdijk Field Research 2005-2006
(last update: 14 August 2010)
Roland-Jan Buijs
Theo Muusse
Mars Muusse
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
Black on Greater Primary Coverts
Overall, 8% (21 birds) of breeding Herring Gulls showed black on the primary coverts. Black was more frequent in males than females (males 12% (n = 146); females 3% (n = 128); Pearson χ2=6,99; P=0,008; df=1). This difference may be due to an age-sex interaction with respect to colonisation, as males return to the colony to occupy territories at younger age than females (Vercruijsse, 1999). For birds of known age (n = 33), the presence of black on the primary coverts is age-related in Herring Gull (b = -1.393, r2 = 0.408, P = 0.014; df = 1; table 2).
The majority (76%) of breeding Lesser Black-backed Gulls showed black on the primary coverts (n = 962) and we found no marked difference between the sexes (males 78% (n = 434); females 74% (n = 496); Pearson χ2 = 2,622; P = 0,105; df = 1). Our data of known-age Lesser Black-backed Gull (n = 76) suggest that both the number of primaries showing black (b=-0.071, r2=0.072, P=0.020) and the presence of black on the primary coverts (b=-0.189, r2=0.046, P=0.068) are age-related (table 2).
We scored 54 adult birds of known age in 6cy-14cy. 41 birds (75%), in all nine age-classes, were found showing neatly demarcated black pigmentation. 62 breeding LBBG in our sample are considered to be ‘sub-adult birds’ showing primary coverts with extensive black markings, pale brown tips and diffuse borders. 666 birds show limited black markings which are neatly demarcated; we consider such birds to be ‘mature adults’ (see plate 3).
Plate 3. Two example primary covert patterns to illustrate the division between ‘sub-adult’ and ‘adult’ Lesser Black-backed Gulls in our analysis. Left: the greater primary coverts in sub-adult LBBG oHZ show extensive dark centres and diffuse borders. Also note the dark centres on the secondaries and brown-black P9 and P10. Right: LBBG yET with neatly demarcated black markings, which are considered to be still possible in ‘adult’ birds. In fact, LBBG yET was ringed as pullus in June 1995, and now in its 12th calendar year.
| . |
LBBG
|
HG
|
||||
| Age |
No
|
Yes
|
n:
|
No
|
Yes
|
n:
|
| 4 cy |
.
|
100
|
13
|
.
|
100
|
2
|
| 5 cy |
14
|
86
|
8
|
40
|
60
|
5
|
| 6 cy |
20
|
80
|
5
|
67
|
33
|
3
|
| 7 cy |
17
|
83
|
7
|
80
|
20
|
5
|
| 8 cy |
8
|
92
|
14
|
100
|
.
|
5
|
| 9 cy |
50
|
50
|
4
|
100
|
.
|
3
|
| 10 cy |
57
|
43
|
7
|
100
|
.
|
1
|
| 11 cy |
50
|
50
|
6
|
100
|
.
|
3
|
| 12 cy |
.
|
100
|
5
|
.
|
.
|
.
|
| 13 cy |
33
|
67
|
3
|
100
|
.
|
1
|
| 14+ cy |
.
|
100
|
3
|
100
|
.
|
5
|
| Whole sample |
25
|
75
|
962
|
92
|
8
|
286
|
Table 2: Black pigmentation on primary coverts in known-age Herring and Lesser Black-backed Gulls (retrapped birds excluded). Values are % for their own age-class. Age in calendar years (CY).
We have illustrated all greater primary wing coverts of known-age Lesser Black-backed Gulls HERE.
Read further on RESULTS: 3. NUMBER OF PRIMARIES WITH BLACK PIGMENTATION >
Lesser Black-backed Gull L.f. graellsii 5cy male 20, 06 May 2006. No black on primary coverts.
Lesser Black-backed Gull L.f. graellsii 6cy male UA, 21 May 2005. No black on primary coverts.
Lesser Black-backed Gull L.f. graellsii 7cy male P8, 21 May 2005. No black on primary coverts.We have illustrated all greater primary wing coverts of known-age Lesser Black-backed Gulls HERE.
Lesser Black-backed Gull L.f. graellsii sub-adult 32, 06 May 2006. Black on primary coverts.
Lesser Black-backed Gull L.f. graellsii 12cy ET, 04 May 2006. Black on primary coverts.
Lesser Black-backed Gull L.f. graellsii 13cy J3, 16 May 2005. Black on primary coverts.
Herring Gull L.a. argenteus 5cy HT, 05 May 2006. No black on primary coverts.
Herring Gull L.a. argenteus 5cy NU, 23 May 2006. No black on primary coverts.
Herring Gull L.a. argenteus 6cy 3T, 14 May 2005.
Herring Gull L.a. argenteus 6cy K4, 09 May 2006.
Herring Gull L.a. argenteus 4cy-5cy 6T, 21 May 2005 & 09 May 2006. Black on primary coverts.
Herring Gull L.a. argenteus 4cy E4, 02 May 2006. Black on primary coverts.
Herring Gull L.a. argenteus 5cy-6cy 13, 05 May 2005 & 09 May 2006. Black on primary coverts.
Herring Gull L.a. argenteus 5cy HK, 04 May 2006.
Herring Gull L.a. argenteus 5cy J2, 05 May 2006. Black on primary coverts.
Herring Gull L.a. argenteus 6cy J7, 09 May 2006. Black on primary coverts.
Herring Gull L.a. argenteus 7cy K2, 09 May 2006. Black on primary coverts.