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Slender-billed Gull is mostly white except pale-grey mantle and black tips of primaries (outer border of 2 secondary is black too). Belly and flanks have very light pinkish tinge. Bill and legs are dark-red. Eyes are whitish, yellowish or reddish; eyelids are red. Juveniles are very similar to juveniles of Black-headed Gull; upperparts are grayish with buffy edges of feathers, tail feathers are with black tips, flight feathers have much of black; bill and legs are orange. Sizes: wing 280 - 330 mm, tarsus 45 - 55 mm, bill 35 - 46 mm. Weight: 271-320 gram.

Biology

The Slender-billed Gull is rare breeding migrant. It inhabits marine shores or salty large lakes, at once bred on fresh lake Kazoty (Biylikol lakes group). Appears in April – early May, in small flocks of up to dozen birds. Breeds in dense colonies on sandy or with scarce vegetation islands or saline soil marshes, numbering up to several hundred pairs, together with Caspian, Gull-billed or Sandwich Terns, Avocet, Great Black-headed Gulls often. Nest is built in shallow hole lined with dry alga and grass, very close (at 20-30 cm) each of other. Clutches of 2-5 eggs in end April - May. After strong gale, nests with eggs to wash away, and birds repeat breeding. Both parents incubate and care for chicks. Flying juveniles recorded in end June - early July. Autumn migration in August - September, latest records in end October.

References

"Птицы Казахстана" том 2. Алма-Ата, 1962. Э.И.Гаврилов. "Фауна и распространение птиц Казахстана". Алматы, 1999. Gavrilov E. I., Gavrilov A. E. "The Birds of Kazakhstan". Almaty, 2005.