Moerdijk Field Research 2005-2006

(last update: 14 August 2010)

Roland-Jan Buijs
Theo Muusse
Mars Muusse


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

Larus fuscus graellsii & Larus argenatus argenteus, Moerdijk, the Netherlands.

In May 2005 we caught 742 breeding within 6 days and in 2006 we caught 764 birds. We obtained the following data:

Darvic code / metal ring in the field
Species in the field
Sex in the field
Wing-span in the field
Tarsus / Head (when necessary) in the field
Grey-tone in the field + Photoshop grey mode
P10 pattern from photo’s
P10 division from photo’s
P9 pattern from photo’s
P5 pattern from photo’s
Black on Bill in Photoshop
Red on Bill in Photoshop
Pigmentation of the iris from photo’s
Orbital ring in Photoshop

There was no overlap between Herring and Lesser Black-backed Gulls in their upperpart tone. The modal (most frequent) grey tone of the Herring Gulls sampled was 5 (range 3-7) while that for the Lesser Black backed Gulls was 11 (range 8-15), based on samples for Herring Gull (n = 292) and Lesser Black-backed Gull (n = 888).

Barth (1968, 1975) has plotted Munsell values for both species. These data were converted to the Kodak Grey Scale by Jonsson (1998). Nominate fuscus from the heartland of its range (SW Finland & NE Sweden) shows grey tones of 13-17 (mean value 14.4). In our Dutch sample, 10% (92 individuals) showed grey tone 13.0 or higher and therefore match pale to average nominate fuscus in the darkness of their upperparts. The modal grey tone among the Moerdijk Lesser Black-backed Gulls is close to the population mean of 11.7 for intermedius from the Swedish SW coast given by (Barth (1975). Recent research and a publication by Andreas Noeske showed similar results for the island Amrum, N Germany.

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