Moerdijk Field Research 2005-2006

(last update: 14 August 2010)

Methods

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).
Birds were classified male argenteus when wings were larger than 430 mm and female when wings were shorter than 410 mm. For birds in the overlapping zone, ‘head+bill’ measurements were used. For males, head+bill was larger than 119 mm and for females head+bill was smaller than ….
For graellsii, birds were classified male when wings were larger than 430 mm and head+bill larger than 115 mm (see also table 1). We scored the upper-part grey tone and primary moult score of each bird in the field. Upperwing, underwing, legs and head were all photographed, with images examined afterwards in Photoshop (CS2) to characterise each bird according to 11 features:

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).

..I	II	III	IV	V	VI
P10 and P9 primary pattern classification in breeding Herring Gulls and Lesser Black-backed Gulls. 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. P10 division diffuse in V and sharp in VI.

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.

LBBG: 0 (0%) o9S, 1 (0-1%) o4X, 2 (1-5%) yE6, 3 (5-10%) o5U, 4 (10-20%) yBK, 5 (>20%) mAV

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.

HG: 0 (0%) m9A, 1 (0-1%) oKW, 2 (1-5%) oL2, 3 (5-10%) m6T, 4 (10-20%) oJ5, 5 (>20%) oKN

Images above. Classification for iris speckling in individual Herring & Lesser Black-backed Gulls. Codes (e.g. M9A) refer to individual birds; see main text for explanation. The iris of LBBG o9S is separated in quarters to illustrate estimations of pigmented surface.

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’.

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