Photo 12 & 13: LBBG 3cy, May 2000, Maasvlakte. 

Compare structural differences in flight between both birds. The left being obviously more slender with narrow and relatively long wings. Some central tail feathers have been moulted during late winter or early spring. This combination points to intermedius. The right bird is a typical second summer in showing a grey saddle, brownish coverts and old tail containing much black.

In the bottom picture: Unmoulted lesser and median under-wing coverts are very dark brown in many individuals. Note the obvious contrast of these feathers against the largely white under parts, paler secondaries and greater under-wing coverts. This bird is actively moulting its inner primaries.