On grey tones:
In Bahrain we used a 1 to 16 greyscale which can be downloaded at http://www.nikhef.nl/~e07/index/rgb.html#Greyscale: Greyscale. It’s the same grey scale used in Adobe Photoshop for instance.
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We printed this grey scale and used it in Bahrain as can be seen in some pictures. Still, the grey tones are “printer setting dependant”, but any bird classified “between 8 and 9” in the field will fall between 8 and 9 under other light conditions as well. Light conditions in Bahrain are supposed to influence both upperparts and paper grey scale in a same degree.
Where groups of gulls
are shown, remember grey tone is dependent of the relative angle between bird
and observer. Also remember immature gulls are often slightly paler than adults
and freshly moulted feathers are deeper grey than bleached, worn feathers of a
previous generation. Judging absolute shades of grey from photos
is hazardous. The variables of emulsion film and the processing chemicals are in
our case met by the use of a digital camera. So, there was no scanning or
preparing of photo images. But to display images on a computer monitor
introduces another enormous variability in the perceived shades of grey (and all
colour), f.i. dependant of the colour setting of our monitor, which is the
reference. We used Abode Photoshop to adjust brightness, contrast and
sharpening. But any of these adjustments were always applied to the entire
image. Nevertheless, be careful judging colours/shades on any computer images of
gulls.
On names:
The white-headed gulls in the Bahrain Section are believed to belong to either:
Fuscus: Baltic Gull.
Heuglini:
Siberian Gull.
Ponticus – Cachinnans – Barabensis – (Mongolicus?): Steppe Gull.
We believe both fuscus and heuglini stand on their own. Fuscus as the smallest, darkest of white-headed gulls in Bahrain. Heuglini at our grey scale is up to three shades darker than barabensis, which is by far the most numerous.
The specific division and distribution of different types within the clinic (?) Steppe Gull-complex remain difficult. In Bahrain, the western type of cachinnans, i.e. ponticus is generally easy to separate from the widespread barabensis. Much more difficult to recognize are the nominate cachinnans. Most confusing is based on the ignorance of variability within this type, regarding facial expression; black-white division in the wing; appearance and size of merged tip and mirror; appearance of p5; presence of grey tongues at the outer primaries… Therefore we join Martin Reid, who wrote:
“… note that all identifications of birds in Bahrain are tentative, especially my assignments to race (ponticus or cachinnans) - please interpret each use of a racial name (xxx) as meaning "appears to be closest to xxx based upon population averages".”
As far as we know, we did not come across any mongolicus.
One adult resembled a taimyrensis. P1-p4 recently moulted, p5-p10 old, mantle and scapulars worn, median coverts all missing, inner three greater coverts new, rest missing, head moulting, bill pale yellow with almost no black markings. But as a type, no sufficient study could be done to a group to build up references.
We would like to thank Howard King, Norman van Swelm, Peter de Knijff and Martin Reid. Their contributions for both the trip and preparations for this site were indispensable. Nevertheless, it is inevitable that there are some identification/aging errors at this site, and we appreciate any comments and suggestions. Please let us know and mail us at: