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
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 | |||||||||||
|
0:
0% |
I:
0-1% |
II:
1-5% |
III:
5-10% |
IV:
10-20% |
V:
>20% |
total
|
yellow
|
orange
|
red
|
total
|
||
| HG ♂ |
10
|
31
|
11
|
2
|
0
|
0
|
54
|
2
|
52
|
0
|
55
|
|
| HG ♀ |
13
|
26
|
7
|
0
|
-
|
-
|
46
|
4
|
42
|
-
|
46
|
|
| total |
22
|
57
|
18
|
2
|
0
|
0
|
100
|
6
|
94
|
0
|
100
|
|
| LBBG ♂ |
10
|
24
|
9
|
3
|
1
|
1
|
47
|
-
|
0
|
47
|
47
|
|
| LBBG ♀ |
13
|
31
|
8
|
1
|
0
|
0
|
53
|
-
|
0
|
53
|
53
|
|
| total |
24
|
55
|
17
|
3
|
1
|
1
|
100
|
-
|
0
|
100
|
100
|
|
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 >
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.
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%.
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%.
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%.
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%.
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%.
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%.
Lesser Black-backed Gull L.f. graellsii male 63, 09 May 2006. Iris speckling: >20%.
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'.
Lesser Black-backed Gull L.f. graellsii male TX, 21 May 2006. Orbital ring score 'orange'.
Lesser Black-backed Gull L.f. graellsii female 13, 16 May 2006. Orbital ring score 'orange'.