This bird was aged as an adult based on the four following criteria.
Adult alula has a pointed profile giving it a spear like appearance.
Juveniles have a rounded profile.
Adult primary coverts have a flat profile and a pale terminal band.
Juveniles have a more rounded profile with a terminal band the same colour as the rest of the feather.
Adult inner primaries show a flattened tip with a step between the inner and outer web.
Juvenile inner primaries have a rounded tip with no step between the inner and outer web.
Adult underwing secondary coverts have a broad flat tip and distinct barring.
Juvenile underwing coverts have a pointed tip and faint or irregular barring.
Based on the wing length of 203mm it was sexed as a male, range being 195-206. the female range is 185-202.
This was the first time I have lamped this field. A word of warning, walk raound the field in daylight first. There was one stage this evening where I lost my bearings for a while and it is a bit disconcerting to realise you are lost. Lesson learnt.