Figure 3: upper-part value & chroma in LBBG
(last update: 04 december 2003)
Herring Gull argentatus
3 from "Taxonomy of Larus argentatus and Larus fuscus
in north-western Europe", by Edvard K. Barth (Ornis Scand. 6, 49-63,
Statistical analysis of colour value (increasing lightness upwards), and chroma notation (increasing saturation to the right) of the three races of L. fuscus. The Danish population is considered to be a partial mixed one. Single lines represent the range. Rectangles indicate one standard deviation on either side of the means. Solid bars indicate 99% confidence intervals for the means. The number of birds in each sample is given.
From Barth's research, interesting points are the homogenous population in isolated locations regarding chroma value. On the other hand, Barth found "markedly heterogeneous population ... in southernmost Sweden and the whole of Denmark and at the southernmost point of Norway as well as on Tarva off the Trontheim Fiord and in East Finnmark, all these areas bordering upon neighbouring races. Immigration may occur in these areas". Still, best features to distinguish intermedius from fuscus (on population level) are colour value and chroma value.
Note the inter-specific population variation and the overlap between the populations. On individual level, Danish birds may overlap in both chroma and colour level with true fuscus from the Baltic and N Norway, where fuscus populations are homogeneous in their very dark upper-parts. Jonsson (BW 11-8, p 303) mentions a 15% overlap in mantle colour between fuscus from the Swedish east coast and intermedius from western Sweden. He therefore concludes that: "... the mere fact that a Lesser Black-backed Gull looks darker than a typical intermedius, and may even appear black-looking, is not enough for a sub-specific identification."
A few notes are necessary: By the time Barth wrote his articles, fuscus was more numerous as a breeding bird in both northern Norway and the northern parts of the Baltic's. In the 70's, the intermedius area Möre-Bohuslän was well defined, compared with fuscus breeding in the northern half of Norway. Nowadays the fuscus populations decreased drastically as a breeding bird in all parts of Scandinavia and has vanished from Kola peninsula and the southernmost Baltic. Now fuscus withdraws, graellsii/intermedius is taking over in abandoned areas like the Danish islands and NW Norway (L. Jonsson in BW 11-8, 1998).