Whitethroat (useful tips for identifying juvenile birds)

This morning I visited a lane near Bodney, Norfolk, where two territories of Whitethroats have been seen this year.  The lane is within a vast expanse of arable with little tall cover.  The wide roadside verges have a couple of well-spaced Hawthorns, otherwise the habitat is one of long grasses, umbellifer species, and low sprawling ground cover.
This morning I watched two pairs of Whitethroats, one of which was accompanied by at least two juvenile birds.  The adult birds typically gave their single, nasally alarm call to warn the juveniles, also the adults were food-carrying.

Juvenile Whitethroat (Note the all dark eye)

All ages and sexes of Whitethroats have the distinctive chestnut wing-panel, the only British species to have this feature, other than the very rare Spectacled Warbler.  Note here the concolourous head and mantle, also, see that the eye of the juvenile bird is all dark, on adults the iris is Orange with a darker pupil.  The other obvious giveaway is the pale gape flanges, an 'elastic' like membrane which allows a wide gape when being fed by adult birds.

Juvenile Whitethroat 10th July.  The dark eye and chestnut wing patches are visible here.

This photograph highlights nicely the chestnut wing patches and tertial fringes, the only British Warbler to have this feature, which also helps separate this species from the slightly smaller Lesser Whitethroat. 

Two juvenile Whitethroats waiting for food 10th July