Saturday, 16 August 2014

Caspian Gull

First-hand experiences of Caspian Gull (Larus cachinnans, Sztyeppi sirály) in Hungary

1. Adult (close to breeding colony) at Hortobágy-fishponds, Hortobágy, Hungary; 25th April 2010

Shape and barepart colours are of more use in the field than is plumage in adult birds:
  • Slender, longish bill without noticable gonys.
  • Small, "beady", darkish eye.
  • Long, prominently sloping forehead - but with a gentle curve. Head profile not as strong or brutal looking as that of other gulls of similar size.
  • Leg colour cannot be seen properly here, but anyway pinkish. Bareparts typically dull even in summer plumage.
 Yellow-legged Gulls (L. m. michahellis) from the East (Eastern Black Sea - Western Caspian Sea region???) migrating through Hungary in autumn [mainly in Oct-Nov] towards the north-west seacoasts of Europe) may also sport finer and dull-coloured bills, but without the longish and slender quality. The head shape of these eastern michahellis birds may also be more gentle than the usual michahellis, but without the prominent slope of forehead. Nesting large gulls in East Hungary (outside the Hortobágy area, esp. in the Kiskunság) are usually considered as L. cachinnans, but they are surprisingly hard to identify, since do not usually show full set of features outlined above, and actually quite featureless in shape and show no diagnostic barepart colouration. They may be hybrid birds (L. michahellis x cachinnans) however, a phenomenon now being increasingly familiar in Poland.

2. First summer at Hortobágy-fishponds, Hortobágy, Hungary; 25th April 2010

Immature birds are not always separable readily from commoner Yellow-legged Gull (Larus michahellis michahellis). Barepart colouration is not much help in immature birds, and for some reason the shape differences listed above for adult birds are not so prominent either - but still valid anyway.

So, in immature birds, we have to revert to plumage marks to look. These are the following:
  • Pale window of inner primaries (resembling to Herring Gull Larus argentatus of similar age)
  • 'Venetian blind'-like (HU: zsalugáter-szerű) pattern on the dark inner primaries (formed by the repetition of two-toned primary feathers - distal webs being dark, inner webs paler)
  • Silvery pale scapulars and mantle/back with few and simple darkish markings  

3. The same individual as in fig. 2, from above

Note the pale inner-primaries window and the 'Venetian-blind' pattern of the outer primaries. Also, pay attention to the silvery and pale mantle, back and scapulars. The bill is longish, gonys is hardly noticable.

4. The same individual as in fig. 2, from below

Underwing including axilliaries is definitely pale/whitish.

5. The same individual as in fig. 2 (with a blue colour - Hortobágy - ring)

Bill colouration makes the gonydeal angle somewhat more discernible from this angle.

Used and recommended references:
Gibbins, C., Small, B. J., Sweeney J. 2010. From the Rarities Committee’s files: Identification of Caspian Gulls. Part I: typical birds. British Birds 103: 142-183.
Malling Olsen, K., Larsson, H. 2003. Gulls of Europe, Asia and North America. Christopher Helm, London.
Van Duivendijk, N. 2011. Advanced Bird ID Handbook: The Western Palearctic. New Holland Publishers.