Moerdijk Field Research 2005-2006
(last update: 14 August 2010)
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coordinators:
Roland-Jan Buijs
Theo Muusse
Mars Muusse
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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
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Larus argentatus argenteus & Larus fuscus graellsii - Moerdijk, the Netherlands
Iris Speckling and orbital ring colour
The majority of Herring Gulls showed some degree of iris speckling (table 7). Over half of the birds fell in category I (0-1%). Overall, male Herring Gulls showed a more densely speckled eye than females (Mann-Whitney U = 7742, Z = -2.496, P = 0.013, male n = 147, female n = 125). For example, seven males scored category III or higher, but only one female. The difference between sexes remains significant when sub-adults are excluded from the analysis (Mann-Whitney U = 6847, Z = -1.967, P = 0.049, male n = 130, female n = 121).
78% of Lesser Black-backed Gulls had no or extremely limited iris speckling (less than 1% speckling: categories 0 and I). The difference between sexes was significant (Mann-Whitney U = 92841, Z = -3.391, P = 0.001, male n = 431, female n = 488), with males having more speckling than females. We found 36 males (including eight sub-adults) with eyes falling into category III or higher but only 8 females. When sub-adults are excluded, the difference between sexes remains significant (Mann-Whitney U = 90245, Z = -2.948, P = 0.003, male n = 414, female n = 486).
Almost all Herring Gulls showed orange orbital rings (94%), with only 18 birds having yellow and one bird (HG NLA 5.363.004) a red orbital ring. Four Lesser Black-backed Gulls scored orange (LBBG yS8, y13, oC9, oTX), with all other individuals having red orbital rings.
|
speckling |
orbital ring |
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0:
0%
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I:
0-1%
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II:
1-5%
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III:
5-10%
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IV:
10-20%
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V:
>20%
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total
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yellow
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orange
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red
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total
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HG ♂ |
10
|
31
|
11
|
2
|
0
|
0
|
54
|
2
|
52
|
0
|
55
|
|
HG ♀ |
13
|
26
|
7
|
0
|
-
|
-
|
46
|
4
|
42
|
-
|
46
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total |
22
|
57
|
18
|
2
|
0
|
0
|
100
|
6
|
94
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0
|
100
|
|
LBBG ♂ |
10
|
24
|
9
|
3
|
1
|
1
|
47
|
-
|
0
|
47
|
47
|
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LBBG ♀ |
13
|
31
|
8
|
1
|
0
|
0
|
53
|
-
|
0
|
53
|
53
|
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total |
24
|
55
|
17
|
3
|
1
|
1
|
100
|
-
|
0
|
100
|
100
|
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Table 7: Iris speckling and orbital ring scores for Herring and Lesser Black-backed Gull. Values are %. Sample size for HG: 284, for LBBG: 919.
Read further on RESULTS: 9 COMMENCEMENT OF PRIMARY MOULT >
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Iris speckling in Lesser Black-backed Gulls |
Iris speckling in Herring Gulls |
Iris speckling: 0%, clean iris |
Iris speckling: 0%, clean iris |
Lesser Black-backed Gull L.f. graellsii 5cy female S9, 21 May 2006. Iris speckling: 0%. |
Herring Gull L.a. argenteus 5cy female HK, 04 May 2006. Iris speckling: 0%. |
Lesser Black-backed Gull L.f. graellsii 8-9cy male J4, 16 May 2005 & 08 May 2006. Iris speckling: 0%. |
Herring Gull L.a. argenteus 13cy male 10, 05 May 2005. Iris speckling: 0%. |
Lesser Black-backed Gull L.f. graellsii 9cy female TT, 21 May 2005. Iris speckling: 0%. |
Herring Gull L.a. argenteus 14cy & 15cy VE, 21 May 2005 & 16 May 2006. Iris speckling: 0% in 2006, but 0-1% in 2005. |
Iris speckling: 0-1% |
Iris speckling: 0-1% |
Lesser Black-backed Gull L.f. graellsii 4cy male SX, 21 May 2006. Iris speckling: 0-1%. |
Herring Gull L.a. argenteus 5cy-6cy male 13, 05 May 2005 & 09 May 2006. Iris speckling: 0-1%. |
Lesser Black-backed Gull L.f. graellsii 10cy female 67, 09 May 2006. Iris speckling: 0-1%. |
Herring Gull L.a. argenteus 7cy female 4T, 16 May 2005. Iris speckling: 0-1%. |
Lesser Black-backed Gull L.f. graellsii 14cy female C5, 08 May 2006. Iris speckling: 0-1%. |
Herring Gull L.a. argenteus 11cy male JK, 06 May 2006. Iris speckling: 0-1%. |
Iris speckling: 1-5% |
Iris speckling: 1-5% |
Lesser Black-backed Gull L.f. graellsii 9cy male AH, 02 May 2006. Iris speckling: 1-5%. |
Herring Gull L.a. argenteus 4cy male E4, 02 May 2006. Iris speckling: 1-5%. |
Lesser Black-backed Gull L.f. graellsii 11cy female LA, 16 May 2005. Iris speckling: 1-5%. |
Herring Gull L.a. argenteus 8cy male KU, 09 May 2006. Iris speckling: 1-5%. |
Lesser Black-backed Gull L.f. graellsii 14cy female UX, 15 May 2006. Iris speckling: 1-5%. |
Herring Gull L.a. argenteus 24cy female PL, 07 May 2006. Iris speckling: 1-5%. |
Iris speckling: 5-10% |
Iris speckling: 5-10% |
Lesser Black-backed Gull L.f. graellsii 4cy male 7N, 09 May 2006. Iris speckling: 5-10%. |
Herring Gull L.a. argenteus 4cy-5cy male 6T, 21 May 2005 & 09 May 2006. Iris speckling: 5-10% in 2005, but less (1-5%) in 2006. |
Lesser Black-backed Gull L.f. graellsii 8cy male CW, 04 May 2006. Iris speckling: 5-10%. |
Herring Gull L.a. argenteus 6cy male 3T, 14 May 2005. Iris speckling: 5-10%. |
Lesser Black-backed Gull L.f. graellsii sub-adult MC, 13 May 2006. Iris speckling: 5-10%. |
Herring Gull L.a. argenteus female 3K, 14 May 2005. Iris speckling: 5-10%. |
Iris speckling: 10-20% |
Herring Gull L.a. argenteus male 44, 16 May 2005. Iris speckling: 5-10%. |
Lesser Black-backed Gull L.f. graellsii sub-adult male CV, 06 May 2006. Iris speckling: 10-20%. |
Herring Gull L.a. argenteus male 4X, 16 May 2005. Iris speckling: 5-10%. |
Lesser Black-backed Gull L.f. graellsii female LF, 13 May 2006. Iris speckling: 10-20%. |
Herring Gull L.a. argenteus male H7, 05 May 2006. Iris speckling: 5-10%. |
Lesser Black-backed Gull L.f. graellsii male BK, 02 May 2006. Iris speckling: 10-20%. |
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Iris speckling: >20% |
Iris speckling: 10-20% |
Lesser Black-backed Gull L.f. graellsii 4cy male S6, 04 June 2006. Iris speckling: >20%. |
Herring Gull L.a. argenteus male J5, 08 May 2006. One bird showing iris speckling: 10-20%. |
Lesser Black-backed Gull L.f. graellsii 5cy male E0, 14 May 2006. Iris speckling: >20%. |
Iris speckling: >20% |
Lesser Black-backed Gull L.f. graellsii sub-adult male LE, 16 May 2006. Iris speckling: >20%. |
Herring Gull L.a. argenteus male KN, 09 May 2006. One bird showing iris speckling: >20%. |
Lesser Black-backed Gull L.f. graellsii female AV, 21 May 2006. Iris speckling: >20%. |
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Lesser Black-backed Gull L.f. graellsii male 63, 09 May 2006. Iris speckling: >20%. |
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Orbital ring score 'orange' in Lesser Black-backed Gulls |
Orbital ring score 'orange' in Herring Gulls |
Lesser Black-backed Gull L.f. graellsii 4cy male S8, 04 June 2006. Orbital ring score 'orange'. |
Herring Gull L.a. argenteus NLA 5.363.004 12 July 2005. One bird showing orbital ring 'orange'. |
Lesser Black-backed Gull L.f. graellsii female C9, 06 May 2006. Orbital ring score 'orange'. |
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Lesser Black-backed Gull L.f. graellsii male TX, 21 May 2006. Orbital ring score 'orange'. |
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Lesser Black-backed Gull L.f. graellsii female 13, 16 May 2006. Orbital ring score 'orange'. |
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