Caught a Casp!

Dutch bird ringer Frank Majoor visited my home town of Leiden, The Netherlands, yesterday to ring some Black-headed Gulls as part of one of his projects.

During one of the sessions I noticed a first-calendar year Caspian Gull (Larus cachinnans) standing between a small group of European Herring Gulls. It stood out not only because of the different plumage (white head, distinctive scapular pattern and a few moulted wing coverts), but also because of its large size and thin, tall legs.

Caspian Gull, 1cy, Y[FF]
First-calendar year Caspian Gull in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

 

Caspian gulls are quite common in The Netherlands but the number of observations of this type of gull are quite low in the Leiden area (partly because not many people keep track of gulls here).

It only took Frank a few moments to catch it, enabling us to take a close-up look of this magnificent bird. What struck us immediately was its large size (especially the bill), which made it quite a challenge to take its measurements, especially using equipment aimed for measuring Black-headed Gulls!

Fortunately Frank carries with him rings for various types of birds, including large gulls. This bird was to be fitted with a metal ring (ringing station Arnhem, code 5463250) and a color ring (Yellow FF) provided by Roland-Jan Buijs. After a quick call to Roland-Jan to make sure the rings were fitted in the right position (metal on the right tibia, color on the left tibia), we made a few identification photos and then released it. It will be interesting to find out where it will be observed over the next years!

Caspian Gull, 1cy, Y[FF]
First-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.
 
Caspian Gull, 1cy, Y[FF]
Tail pattern of first-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.
 
Caspian Gull, 1cy, Y[FF]
Wing pattern of first-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.
 
Caspian Gull, 1cy, Y[FF]
Flight-shot of first-calendar year Caspian Gull Yellow FF in first-winter (first cycle) plumage. Leiden, The Netherlands, 24 December 2011.

Some of the identification features of a first-calendar year Caspian Gull, distinguishing it from a European Herring Gull or a Yellow-legged Gull of the same age include:

  • Thin high legs, showing much tibia (upper leg)
  • Light-grey scapulars with distinctive dark anchor
  • Moult in the wing coverts
  • White head with light streaking and lack of an eye patch as for Yellow-legged
  • Large black bill, somewhat parallel and no blunt tip
  • Inner primaries with light inner web and dark outer web (creating a ‘Venetian blind’ effect)
  • Small white tips to the inner primaries (apical spots)
  • Narrow banding on the tail above the subterminal band

All-in-all a great moment and a nice way to end the year with!

Caspian Gull, 1cy, Y[FF]
Me with first-calendar year Caspian Gull Yellow FF.
 
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