OK so this is a bit late.

A friend of mine, Robin Sellers, has done a lot of work with cormorants in
England. Drying appears at least to be the major function of holding their
wings out with birds orienting themselves to face the wind (depending on
how strong it is) and more importantly the sun. Birds after prolonged
fishing attmepts will periodically leave the water to dry themselves before
returning to fish - this seems to be independent of whether they actually
catch anything which points to drying as a prime motivation.

The cormorants (Phalacrocorax carbo) also flag their wings to presumably
increase the drying effect.

In Scotland, shags (Phalacrocorax carbo) only occaisonally spread their
wings- these birds are only about 2/3 size of P. carbo so the cost of
having waterproof and hencve bouyant feathers is not as great.

A good place to look at this in Seattle would be on the boom opposite 520
in Union Bay. Some diligent soul could set up a telescope from Foster Island
or perhaps Montlake (to get a better angle) and record the times the birds
spend "drying" themselves and see what the correlations are - weather,
time of day, number of birds, etc.

There might be a social signalling component to this who knows ?

Stuart