Larus cachinnans

(last update: February 16, 2013)

Coordinator:
Peter Adriaens (Belgium)
Ies Meulmeester (Netherlands)

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cachinnans plumages

Larus argentatus sensu lato 4P18 adult, May 05 2014 & October 25 2014, Zastów Karczmiski & Wroclaw, Odra River, Poland. Picture: Łukasz Bednarz ringing team.

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Location: Zastów Karczmiski, Poland - colony at the banks of the Middle Vistula river.
In 2004 240 breeding pairs (95% cachinnans, <5% argentatus). (Ornis Fennica 2011 88, 80-89) and in 2012 592 pairs (90% cachinnans, <10% hybrid / argentatus) and possibly Larus michahellis (pers comm. Łukasz Bednarz).

Middle Vistule river is a location where several taxa breed: see composition. Since this is a mixed breeding population where hybridisation is not uncommon, the ringing centre in Poland decided to label birds "Larus argentatus sensu lato". Still bulk of the breeding birds in Middle Vistula region show features of cachinnans.

below: Larus argentatus sensu lato 4P18 adult, May 05 2014, Zastów Karczmiski, Poland. Picture: Łukasz Bednarz ringing team.

Breeding bird trapped at the nest, showing some similarity to argentatus (F2?) in clean iris, obvious gonys (Bill ratio: 3,15), really pink legs and orange orbital ring. All these features can be found in cachinnans as well however.
Adult, with no speckling in iris. Orange orbital ring and gape. No red on upper mandible; faint black on the upper and faint black on the lower mandible. Pink legs.
Deep white tongue on P10 (ends just angular), incomplete black band on P5; no spot on P4. P1 dropped, PMS=1.

below: Larus argentatus sensu lato 4P18 adult, October 25 2014, Wroclaw, Odra River, Poland.