The shade of "adult gray" across the back and upper wings of mature birds (and on the back and scapulars on younger birds-- like the second winter bird in the middle above) is one of the least variable characteristics of gulls. However, due to different lighting in field conditions, it may be one of the least useful. This gray color, often with a bluish, flat gray, or brownish hue, depending on the species, may appear lighter or darker depending on the angle of the sun or the angle of the bird. The gray often appears darker on birds seen from the rear, lighter (and more blue) when seen from the front. Direct sunlight may produce all kinds of strange effects. In general, this is only a good field mark when birds can be compared side by side, facing the same direction, preferably on an overcast day that eliminates sharp shadows. The following chart may give the misleading impression that birds farther down on the list will always appear darker than birds higher up. In fact, many of the shades are so close that those within 0.3 (on the Munsell scale used) of each other will appear extremely close in color, often indistinguishable to the human eye. Thus, the mantle shade of gray is an excellent field mark when comparing species that are quite different from each other, but of limited use when comparing birds with similar shades of gray. It should also be noted that variability is most common among those species with subspecies that are most defined by mantle shade. For example, Lesser Black-backed Gulls, especially graellsii and intermedius, are probably the most variable.

MUNSELL VALUE (10=white; 1=black)
(colors here are approximate; not exact)

7.5 7.0

Glaucous Iceland

6.5 6.0

Ring-billed; Herring (argenteus) Herring (smithsonianus)

5.5 5.0

Thayer's; Caspian (cachinanns) Common (canus) Yellow-legged (michahellis) Glaucous-winged Mew; Common (henei) Herring (argentatus); California; Kamchatka Vega (birulai)

4.5 4.0

Mongolian (mongolicus) Vega (vegae) Yellow-legged (atlantis) Steppe (barabensis) Armenian (armenicus) Heuglin's (taimyrensis) Western (occidentalis) Heuglin's (antelius)

3.5 3.0

Black-tailed Lesser Black-backed (graellsii) Western (wymani); Yellow-footed Slaty-backed

2.5 2.0

Lesser Black-backed (intermedius) Great Black-backed; Kelp Baltic (fuscus)