In preparation for fitting several juvenile Lesser Black-backed Gulls with GPS loggers in the IJmuiden Forteiland colony in the Netherlands, we closely monitored the development of several young birds.
This resulted in a nice photographic overview of the development of these birds, from fluffy chick to fully feathered juvenile.
One such example is Green YCWU, who eventually was fitted with a GPS logger.
The photos were taken between 3 June 2019 and 22 July 2019 when it was between 3 and 52 days old.
Click for a larger view.