Moerdijk Field Research 2005-2006
(last update: 14 August 2010)
|Larus argentatus argenteus & Larus fuscus graellsii - Moerdijk, the Netherlands
We sampled birds on the large industrial complex at Moerdijk (51.41N 04.36E). All sample birds were trapped at the nest using walk-in cages, as described in Sibly (1983). The nests were selected randomly. Species were separated using the combination of leg colour in combination with upper-part grey tone and orbital ring. Individuals were sexed in the field using head and wing measurements, as Niethammer (1937), Harris and Hope-Jones (1969) and Coulson et al (1983).
1. Grey tone of upper-parts. Scored 1-20 on Agfa grey scale (which is similar to the Kodak 20 step grey scale) in 0.5 classes. See Goethe (1961) and Jonsson (1998) for discussion of the use of grey scales and measurements. We first scored grey tone in the field (in the shadow) and photographed each bird with the scale held next to its wing, to optimise parallel light conditions for feathers and grey scale simultaneously (see for example plate 7). Data were then validated from the photographs, using Photoshop ‘grey scale’ mode to correct for brown hue and chroma.
2. Black on greater primary coverts. Scored as either present (+) or absent (-). A bird is scored positive only when pigmentation exceeds the width of the shaft.
3. Number of primaries with black pigmentation. Small black sub-terminal spots are included and scored positive.
4. P10 and P9 primary patterns. Following Goethe’s classification, we used six classes to characterise these feathers. I: No mirror. II: Mirror on one web. III: Full sub-terminal black band, mirror on both webs. IV: Sub-terminal black present, but band broken. V: No sub-terminal black, mirror completely merged with tip. VI: ‘Thayeri’ pattern, medial band not reaching the feather-edge of the inner web. For more details, see plate 1 and Goethe (1961).
P10 black/grey division: 2 classes. Division between grey inner web and black outer web scored either sharp or diffuse. For more details, see Barth (1975) and plate 1.
5. P5 primary pattern. Five classes. I: Complete sub-terminal band. II: Sub-terminal band broken, but black on both webs. III: Sub-terminal black present on one web, sharply defined. IV: Sub-terminal black present on one web, diffuse marking. V: No black present. For more details, see Goethe (1961).
6. Red gonydeal spot on upper mandible. Scored as either present (+) or absent (-). A bird is scored positive when the modal red tone of the lower mandible is measured on the upper mandible (see plate 4). We used the Photoshop eye-dropper tool for scoring.
Black on lower and upper mandibles. Scored as present (+) or absent (-). A bird is scored positive when a black value is measured in Photoshop. Using this method, small black markings on the bill are scored the same as an extensive black band.
7. Iris speckling. Six classes. 0: No speckling. I: Speckling < 1% of surface. II: Speckling 1-5%. III: Speckling 5-10%. IV: Speckling 10-20%. V: Speckling > 20%. We did not score so-called ‘clouded’ irides, as true black values are not present in such iris markings. See plate 2 for example of birds in each class.
Orbital ring colour. Three classes. I: Yellow (ffff00-ffa800 on colour scale in Photoshop). II: Orange (ff5800-ffa800). III: Red (ff0000-ff5500).
8. Primary Moult Score for left wing (ranges from 0-50). Following Stewart (2006), we use six classes. 0: Old feather. 1: Missing feather, new feather in pin. 2: New feather visible, < 1/3. 3: New feather, 1/3 2/3. 4: New feather, > 2/3, but still waxy sheath. 5: New feather fully grown. For more details, see Stewart (2006).
All data generated using these scoring protocols were analysed using SPSS 12 for Windows. In the text which follows, we refer to individual ringed birds, where mint-green rings are ‘m’; yellow rings are ‘y’ and orange rings are ‘o’. The notation for Herring Gull mint S0 is therefore ‘HG mSO’.
Read further on RESULTS: 1. UPPERPART GREY TONE >
|Lesser Black-backed Gull L.f. graellsii U3, 28 May 2006. Ringed adult at the nest. Ringed female on 21 May 2005.|
|Lesser Black-backed Gull L.f. graellsii trapping adults using 'walk-in cages'.|
|Herring Gull L.a. argenteus female HP, measurements of wing length on adults.|
|Lesser Black-backed Gull L.f. graellsii 7X, measurements of 'head+bill' on adults in the field.|
|Lesser Black-backed Gull L.f. graellsii 63, measurements of grey tone on adults.|
|Herring Gull L.a. argenteus 8cy KU, measurements of grey tone on adults.|
|Herring Gull L.a. argenteus J5, measurements of grey tone on adults.|
|Herring Gull L.a. argenteus 5cy J2, 05 May 2006. Black on primary coverts.|
|Herring Gull L.a. argenteus 6cy K4, 09 May 2006. No black on primary coverts.|
|Lesser Black-backed Gull L.f. graellsii 14cy UX, 15 May 2006. Black on primary coverts.|
|Herring Gull L.a. argenteus 9cy P3, 16 May 2005. P4-P10 with sub-terminal black.|
|Herring Gull L.a. argenteus NLA 5.363.004 12 July 2005. Thayeri pattern on P9 and P10.|
|Herring Gull L.a. argenteus 17cy female 1A, 04 May 2005. Red on um, black on um and lm.|
|Herring Gull L.a. argenteus female PN, 07 May 2006. Red on um, no black on the bill.|
|Lesser Black-backed Gull L.f. graellsii 8cy male VH, 08 May 2006. Red on um, black on um and lm.|
|Lesser Black-backed Gull L.f. graellsii 8cy male 3N, 06 May 2006. No red on um, black on um and on lm.|
|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%.|
|Herring Gull L.a. argenteus NLA 5.363.004 12 July 2005. Exceptional bird: only HG showing orbital ring 'red' in our sample.|
|Lesser Black-backed Gull L.f. graellsii female C9, 06 May 2006. Exceptional bird: only four LBBGs have orbital ring score 'orange'.|