Top: group of adult Slender-billed Gulls, Muharraq, Bahrain, February 25 2001.

Below left: head of an adult Slender-billed Gull, port of Manama, Bahrain, February 27,2001.

Slender-billed Gull is a small to medium gull, only slightly larger than Black-headed Gull. In summer plumage, it lacks a dark hood on the head, but remarkably, as in Black-headed Gull, in winter it develops a dark patch on the ear-coverts (although much smaller). The most noticeable feature in Slender-billed Gull is the long neck, especially when alarmed. Furthermore, the head is elongated with a sloped forehead and the bill is particularly slender. Slender-billed Gull breed commonly in isolated colonies in the Mediterranean and along the shores of Russian steppe lakes (e.g. Black Sea, Caspian Sea). It winters south along the west coast of Africa, the Mediterranean and to the east: the Arabian peninsular and western India. Most of the description below follows from P.J. Grant: “Gulls, a guide to identification”. 1CY SLENDER-BILLED GULL Juveniles show a less well-defined brown bar on the median and lower lesser coverts than juvenile Black-headed Gull. Also it lacks the extensive buff-brown wash on the crown and ear-coverts. Juvenile Slender-billed has a predominantly pale head. In Black-headed Gull, the buff extends on the sides of the breast and on the mantle and scapulars, where the feathers become more ginger-toned and show white fringes. This ginger tone is missing in Slender-billed, which has the mantle and scapulars grey-brown. The brown tertials are normally broader fringed grey. The inner greater coverts show an extensive dark brown centre, but from greater covert #5 outwards, the juvenile greater coverts are predominantly grey. The white tail shows a clear black tail-band. The partial autumn moult (post-juvenile moult into so-called "first winter" plumage) starts right from the moment the nests are abandoned and is completed by September. This partial moult includes the head and under-parts and often median and lower lesser coverts are included. The head, neck and under-parts turn all white except a small dark spot near the eye and ear spot (of variable size). The new mantle and scapulars are moulted to second generation feathers which are all grey. If median and lower lesser coverts are involved, they are replaced by all-grey feathers as well, similar to the juvenile outer greater coverts (although the first replaced feathers may still show a dark wedge in the centre). The tertials are normally excluded and remain juvenile, but some birds include the upper two or three tertials in this partial moult. 2CY SLENDER-BILLED GULL Next moult takes place in early spring (from February to April into so-called "first summer" plumage) and includes again the body and head. By now, the head turns pale grey without ear-spot. All wing-coverts, remiges and rectrices become strongly worn and the dark bar on the lower lesser coverts bleaches to very pale brown. In a small sample of 2cy birds in Bahrain, quite some birds started to moult outer median and outer lower lesser coverts in this partial moult. In the images of 2cy Slender-billed Gulls in February and March, presented on this web-page, it is obvious that median and lower lesser coverts have been moulted: the dark centred juvenile feathers are replaced for plain grey second generation feathers. As the fringes of some of these feathers are still pretty neat, it is expected these feathers were moulted late in winter. Second generation feathers moulted earlier (September) show extensive wear already (note the wear in the upper tertials of the bird in the upper image on this page). Commonly, the central tail-feathers are included in this partial moult. From June into October the complete moult starts with the inner primaries. The second generation outer primaries will show more white: the partial black outer-web on the primaries P7-P9 (prominent in first generation primaries) is missing in the second generation flight feathers. Again, P10 has a black outer-web. In general, the second generation primaries resemble those in Black-headed Gull. The breast and belly develop a pink cast, variable in extend and hue. The tail is moulted to all-white feathers, the iris turns white to greenish, the bill turns dark red with the legs slightly paler red. Only a few individuals can be recognised as 2cy (second calendar year) birds in October by the primary coverts, which may still show some dark markings or slightly brownish cast on the centre of a tertial. Otherwise, most 2cy Slender-billed Gulls from October are indistinguishable from adults. 3CY & ADULT SLENDER-BILLED GULL Next moult (to summer adult plumage) starts in February and ends in April. It’s a partial moult, including the body and head: the head becomes all white, sometimes with a pink hue. Adult birds develop a strong pinkish wash on the breast and belly. From June into October the complete moult starts again with the inner primaries. When this moult is completed, Slender-billed is in so-called "adult winter" plumage. In general the colour of bare parts is somewhat duller and the head shows a small ear-spot on the rear ear-coverts. Measurements in mm’s wing: 278-320, tail: 110-125, bill: 35-46, tarsus: 46-54; n = 24.	End of February in the Arabian Gulf: still 1.000's of Slender-billed Gulls present. Slender-billed Gull 2cy, Manama, February 2001. Slender-billed Gull 2cy, Manama, February 2001. Slender-billed Gull 2cy, Manama, February 2001. Slender-billed Gull, 3cy, Manama, February 2001. In this plumage, Slender-billed Gull normally show adult-like upper-parts. Slender-billed Gull 3cy, Manama, February 2001. Slender-billed Gull adult, Manama, Bahrain, February 2001. Slender-billed Gull adult, Manama, Bahrain, February 2001. Slender-billed Gull adult, Manama, Bahrain, February 2001.