While I was browsing an old British Birds, I found the following note
(edited for length)

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Underwing of adult Ross's Gull
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Most literature concerning Ross's Gull mentions the underwing colour of
adults as being grey, and it is often depicted as looking almost white.

(snip)...during my observations of three adult Ross's Gulls on the North
Yorkshire coast, I noted that under field conditions the underwing
appears very dark, usually blackish, offering contrast with the more
translucent trailing edge.

I made particular note of theis whilst observing the bird which
frequented Filey Brigg during 17-10 February 1983. At all angles
(although it did not fly directly overhead) and under different lighting
conditions, the underwing always looked blackish, the darkness
accentuated by the white, translucent trailing edge, and a triangular
patch of grey feathers from the leading edge at the base of the wing,
across the axillaries [he refers here to the two photos published with
the note]. Even ;when at rest, the darkness of the undersides of the
primaries was visible, contrasting with the pale shaft of the outermost
primary.

[Paraphrasing: Balch et al (1979) report that a Massachusetts Ross's gull
showed blackish underwing, but an Illinois bird had the wing "the same
color as the upperwing."] One possibility that has been suggested by
Grant (in litt.): that the tone of grey on the underwing of Ross's Gull
may be related to age, as is the case with the Little Gull, where
first-years are white, second-years grey, and third years/adults are
blackish; but as yet there is no evidence for this from the skins he
examined....[possibility of confusion with Little Gull discussed]



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the note was by P J Dunn, 25 Wreyfield Drive, Scarborough, North
Yorkshire YO126NP.

I did not get the exact citation when I copied the note - I
believe it was British Birds, Volume 77: pp 23-24, but I did not note
what year volume 77 came out.

Dunn cites these two works:

Balch, L G, Bohlen, D D, and Rosenband, G B. 1979. The Illinois Ross's
Gull. American Birds 33: 140-142

Grant, P J 1982. Gulls: a guide to identification. Calton

I brought it up because several observers of the McNary dam bird noted
the dark underwings, especially in contrast to the Bonaparte's gulls
there. And my field guides do show a lighter underwing for Ross's than
the bird in the field showed. Some possible explanations for the
variation (other than age):

--Feather wear or fading. The McNary's bird was quite pink, and it
may have just finished its fall molt. Perhaps the dark underwings fade
as the feathers get older. Perhaps the pink fades, too, as I believe it
does for the Roseate Tern as the season progresses.

--Individual variation






Chris Hill
Zoology Department NJ-15
University of Washington
Seattle, WA 98195
cehill at u.washington.edu