Subject: [BIRDWG01] gull mantle colors
Date: Mar 20 09:26:14 1997
From: Jerry Tangren - tangren at wsu.edu


tweets--the following might be of interest to gull watchers
--JT

>X-Sender: dsibley at pulsar.net
>Date: Thu, 20 Mar 1997 10:42:03 -0500
>Reply-To: NBHC ID-FRONTIERS Frontiers of Field Identification
> <BIRDWG01 at LISTSERV.ARIZONA.EDU>
>Sender: NBHC ID-FRONTIERS Frontiers of Field Identification
> <BIRDWG01 at LISTSERV.ARIZONA.EDU>
>X-PH: V4.2 at pegasus
>From: David Sibley <dsibley at PULSAR.NET>
>Subject: [BIRDWG01] gull mantle colors
>To: BIRDWG01 at LISTSERV.ARIZONA.EDU
>
>I was recently looking at specimens at Yale University and pulled out one or
>two adult specimens of each of the North American Gulls which I then
>arranged in a series from lightest to darkest mantle color with the
>following results.
>
>There was little variation in mantle color within each species, aside from
>darkening of some individuals due to obvious soiling or staining
>post-mortem. The collection there was lacking adult Black-tailed, Kumlien's,
>Vega, and Yellow-footed, but all other species are listed here. Species are
>grouped with similar mantle colors and listed from lightest to darkest
>within each group. The groups are somewhat arbitrary but seemed helpful to
>indicate breaks in what is a near continuum of mantle color.
>
>
>Glaucous (atlantic birds ~ Barrow AK)
>Iceland (one Greenland bird)
>Ross' (slightly darker gray than preceding)
>
>Black-headed
>Little
>Ring-billed (slightly bluer?)
>Herring
>Bonaparte's (slightly but distinctly darker than Black-headed)
>
>Thayer's
>Yellow-legged michahellis
>Mew canus
>
>Glaucous-winged
>Mew brachyrhynchus
>California (subspecies comments below)
>Black-legged Kitiwake
>Western occidentalis
>Sabine's
>
>Red-legged Kittiwake
>Franklin's
>Laughing
>Lesser Black-backed graelsii
>
>Heermann's (brownish)
>Western wymani
>Slaty-backed
>
>Great Black-backed
>Lesser Black-backed fuscus
>
>Kelp
>Belcher's - these two species distinctly darker and brown-tinged
>
>This is based strictly on a few specimens and can certainly be refined by
>checking other specimens and by field testing.
>
>California Gull subspecies were mentioned a while ago referring to a paper
>by Joe Jehl. Unfortunately his description of the new subspecies
>albertaensis does not include any actual measurements of mantle color or any
>discussion of variation in mantle color. I have seen little variation
>despite serious looking. Albertaensis averages larger in all measurements
>than californicus but there is evidence of a cline in size and females of
>albertaensis are equal to males of californicus. Thus it must be virtually
>impossible to distinguish birds in the field, which matches my experience in
>California attempting to do just that. I think it is unwise to attempt to
>identify subspecies of California Gull in the field based on current
knowledge.
>
>I have one further esoteric point regarding wing structure of large gulls.
>This may be of interest only to illustrators and possibly very serious
>gullwatchers but I have noticed that the outer 4-5 secondaries and their
>coverts are distinctly pointed, longer than the other secondaries and
>coverts, and intermediate in color between the inner secondaries and the
>primaries. This is clearly visible in many photos in Grant. The same feature
>is visible in hawk photographs in Wheeler and Clark, and presumably occurs
>in all large, long-winged birds. It seems most obvious on immatures. These
>feathers are also sometimes visible on a perched bird e.g. Grant photo 501 -
>the white-tipped feathers just visible beneath the lowest greater secondary
>coverts. Not something one can use every day but it may lead to greater
>precision in describing the wing pattern of immature gulls to distinguish
>between the inner and outer secondaries.
>
>David Sibley
>Cape May Point, NJ
>