Another examle of a 5th-calendar year European Herring Gull Larus argentatus argenteus showing sub-adult features in its plumage. Most interesting are the sub-adult tertials.
Green YBPS was ringed as a 4th-calendar year in June 2014 while breeding in the gull colony of IJmuiden (Forteiland), the Netherlands. It was seen breeding again in the same colony this year, showing black markings in the central tail feathers, a brown hue to the inner greater coverts and brown in the tertials.
The brown marks in the tertials are especially rare for European Herring Gulls older than 4th calendar year and is something that I relate more to American Herring Gulls (see Tertial spots in sub-adult and adult gulls).
This is only the second time that I have encounterd an adult Herring Gull in Europe with tertial markings.
I observed Green YBPS on several occasions during the breeding season but only managed to get a good video and photos on 22 June 2015. Unfortunately I was not able to get a shot of YBPS with spread wings.
With un-ringed partner:
As a 4th-calendar year
For comparison, here is an image of Green YBPS from June 2014: