Photo 4: LBBG sub-adult, 19 November 2000, Westkapelle, the Netherlands.

First very obvious clues for immaturity are the black centres of the fresh tertials (note the fresh fringes of these feathers) which directly point to 3cy or 4cy birds when combined with the white tips of the outer primaries. 2cy LBBG would probably not show such white tips and in 5cy the tertials may be expected to be plain adult-like grey and the primary tips would probably be larger, like the adult in the bottom picture. In the bottom picture, note also the relatively pale yellow, almost pinkish legs of the sub-adult.