IJmuiden Project - Fred Cottaar, José Verbeek, Maarten van Kleinwee & Mars Muusse

(last update: January 01, 2023)

Lesser Black-backed Gull (graellsii) F2-hybrid Y.BWN 1CY, June & August 2015, IJmuiden, the Netherlands. Picture: Mars Muusse & Maarten van Kleinwee.

Ringed as pullus in season 2015 at Forteiland, IJmuiden. Ringed by Fred Cottaar ringing team.

Green YBWN is an offspring of two ringed adults: Lesser Black-backed Gull graellsii YASC and (presumed) hybrid graellsii x michahellis YAHH. This makes YBWN an F2 hybrid (second generation hybrid from michahellis), as is the sister/brother YBWP. If examined into the smallest details, one may find traits that may indicate this michahellis influences (e.g. inherited may be pale on outerwebs of inner primaries), but probably this may also be found in pure graellsii populations: phenotypically YBWN is a graellsii in all respects. Its a gentle bird, probably a female. It will be interesting to measure upperpart grey tone once this bird is in adult plumage.

Two papers have been published on the occurrence of michahellis and its hybrids in this colony:
- Dutch Birding 2004-1 "Yellow-legged Gulls and hybrids breeding at IJmuiden", by Fred Cottaar.
- Dutch Birding 1994-6 "Geelpootmeeuw gepaard met Kleine Mantelmeeuw broedend te IJmuiden", by Fred Cottaar & Kees Verbeek.

Lesser Black-backed Gull (graellsii) F2-hybrid Y.BWN 1CY, August 17-18 2015, IJmuiden, the Netherlands. Picture: Mars Muusse.

Local juvenile in pooring rain. Fresh plumage. Assumed female (code F0).

Lesser Black-backed Gull (graellsii) F2-hybrid Y.BWN 1CY, August 02 2015, IJmuiden, the Netherlands. Picture: Maarten van Kleinwee.

In very fresh plumage there are some tiny white tips to the outer primaries. Such tips may be more common in michahellis than they are in graellsii.

Lesser Black-backed Gull (graellsii) F2-hybrid Y.BWN 1CY, June 29 2015, IJmuiden, the Netherlands. Picture: Maarten van Kleinwee.

When processed while ringed.

Unfortunately, bird was found death while migarting south on October 05 2015 along the Atlantic coast of Algarve, Portugal (halfway Quarteira and Portimao). Cause of death unknown. Recoveries: