Most bird molt twice a year. The timing of those molts and the
number of feathers molted vary by species. Generally, the basic plumage
refers to what most field guides refer to as winter plumage. It is the
dull, boring plumage usually seen in the winter. Alternate plumage is also
called breeding or nuptial plumage and usually brighter. In some birds,
such as chickadees, alternate and basic plumage looks exactly the same even
though a molt is involved. Other species look very different.
Waterfowl do things a bit differently. Most birds molt their flight
feathers one at a time in sequence. Waterfowl drop all of their flight
feathers at once and go through a brief period of total flightlessness.
During this period, the males molt their body feathers and look like
females. This camouflages them better and they are less obvious during this
vulnerable period. Then the flight feathers grow back and they can fly
again. Gradually, they molt out of the female-like plumage and into the
breeding plumage they will wear for most of the year. As Michael Dossett
pointed out, ducks court during the winter so they wear their breeding
plumage all winter long! There is differences in the timing of eclipse
(Ruddy Ducks, for example, start later and retain it longer). The females
also molt all of their flight feathers, usually while accompanying
flightless young. They do not appear different except they have no flight
feathers. Geese also molt all of their flight feathers at once. They do
not have a separate body plumage for this flightless period; I assume their
size or breeding habitat makes them less likely to be preyed upon while they
are flightless. Some waterfowl species do things differently; for example,
both sexes of Oldsquaws change plumage during the winter. I assume they go
through a flightless period but I don't know for certain. They definitely
molt twice a year.
I hope that helps. I agree with Hal Opperman; the references he
listed are a good place to learn about plumages.

Cheers
Deb Beutler

Deborah K. Beutler
Department of Zoology
Washington State Univeristy
Pullman, WA

dbeutler at wsunix.wsu.edu