Myself and other banders in Scotland were catching big numbers (thousands)
of snow buntings in the early 90's. There are birds from Scandanavia and
Iceland present (though mostly from Iceland as it turned out) however all
the identification guides were written for Scandanavian birds which are
different from Icelandic ones so initially we had a difficult time ageing
and sexing birds.

We spent a LOT of time with live birds, skins and photographs trying to
identify criteria to separate ages and sexes. Only after a good deal of
practice were we able to sort out most of the males. The contrast between
the primaries and the rest of the underwing is a great characteristic - in
males the contrast is sharp, females not sharp though there is a range and
it is not always possibly to sex every bird. It is possible to see this in
the field but you need to be close. Ageing females is much harder and can be
very subjective. I can't remember all the different criteria to sort them
out but it was not straight forward.

Do not use the shape of the tail feathers to age a bird. It is extremely
unreliable for birds in the hand. In the field.. forget it.

The amount of white on the tail feathers is extremely variable in European
Snow Buntings so I would use caution.

Snow bunting plumage is designed to change colour through feather wear - the
lovely black and white breeding plumage of males is a result of all the
feathers being worn down rather than a molt. The citeria Pyle gives about
sexing using back feathers with black centers is going to be affected by
feather wear so again I would be cautious.

Stuart
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Stuart MacKay, Lisbon, Portugal