The general issue of plumage terminologies was broughtup some months ago
(I think by Michael Price, but I'm not sure). As one person already posted,
the answer lies in understanding Humphrey and Parkes' terminology.
Unfortunately, very few people really do understand this, and to do so
requires sitting down and readsing the original paper (Auk 1959, vol 76:1-31).
It is true that alternate plumage often IS the plumage that birds breed in,
however, i.e. there is a correlation; however, it is completely wrong to
EQUATE the two as if, by definition, they are the same thing.

Chris Thompson, Ph.D.
Research Scientist
Washington Dept. of Fish and Wildlife