Herring Gull- Zilvermeeuw (argentatus & argenteus)

(last update: 30-9-2009)

Herring Gull (argenteus) YAAH 11CY, August 31 2009, IJmuiden, the Netherlands. 

Local 11cy argenteus, ringed as pullus at IJmuiden 05 July 1999, and re-ringed in 2008 as breeding adult on the nest when a darvic ring was added. P5 fully grown, P8-P10 old. Below pictures the life history has been added; see how readings changed dramatically after adding the darvic ring.

The IJmuiden Ringing Team (Fred & Kees) ringed Herring Gulls and Lesser Black-backed Gulls at Forteiland, IJmuiden in 2008-2011, using green darvic rings, starting with Y for borh species (so codes read Y.xxx).
Early in the season (May), adults were caught at the nests and ringed, late June the juveniles were caught and ringed as well.

This page shows an example of birds from this IJmuiden project. All observations of ringed birds from this project can be sent to Kees Camphuysen at NIOZ, Texel (mail camphuys at nioz dot nl).

From June to December, adult argentatus undergo a complete moult resulting in so-called "winter plumage". By August, the first neat streaks can be found on the crown and hind-neck. After the complete moult is finished by late autumn, the head will show extensive 'winter streaking', often neat fine streaking in sub-adult argentatus. 
By the end of the complete moult (sometimes mid-January in argentatus), the scapulars, mantle, all the wing-coverts, rectrices and remiges will be replaced. From June onwards, the new plain grey wing-coverts are moulted in, starting with the outermost median coverts. 

Adult northern argentatus show a different pattern in the outer primaries, compared to argenteus. In argentatus, especially from northern Scandinavia, the black marking on P5 is very limited and, if black on P5 is present, this black has diffuse edges. But often, these black sub-terminal markings are completely lacking on P5. In Baltic argentatus populations, black on P5 is confined to the outer-web, with sharply defined edges.
Argenteus normally has a black sub-terminal band on the top of p10, dividing the tip from the mirror. If the black sub-terminal band on P10 is broken, the outer-web of p10 still shows black marking. Argentatus normally completely lacks sub-terminal markings, also on the outer-web of P10. Some argentatus completely lack black on the edge of the inner-web, creating a so-called "thayeri pattern". 

The iris is clearly yellow in summer in most argentatus, but some sub-adult argentatus will keep the iris amber to dark brown.

below: Life history for YAAH

Nice to see, how recovery rate increased by attaching the darvic ring!