Rare example of an adult Lesser Black-backed Gull showing tertial spots, seen in the gull colony of IJmuiden Forteiland, the Netherlands, April 2018.
The gull in question is Green YAKU, ringed as an adult in the colony in 2009, making it older than 13 calendar years in 2018.
I observed YAKU again in July. By then, the greater coverts were very worn leaving much of the tertials exposed and making the spot(s) even more visible.
It is my first example of a Lesser Black-backed Gull showing tertial spots, see the references that I’m keeping in Tertial spots in sub-adult and adult gulls. It is therefore also the first time that I have observed it in YAKU. During previous observations dating back to 2010 I never saw this characteristic in this bird. Interestingly, this means that it can suddenly occur in adults of a relatively old age as well.
Above: YAKU, October 2016, IJmuiden beach, the Netherlands. Photo: Mars Muusse, gull-research.org.
Above: YAKU, October 2015, IJmuiden beach, the Netherlands.
Above: YAKU, Katwijk aan Zee beach, the Netherlands, October 2013.
Above: YAKU, Wijk aan Zee beach, the Netherlands, September 2010.