just looked around google i believe they are egrets. the white ones will turn pink from eating the crawfish.Are they gannets?
the dark ones probably are the eastern reef egrets.Do the white ones have a spoon shaped bill? If so, they're some kind of spoonbill( http://en.wikipedia.org/wiki/Spoonbill ). If they have long thin bills, my guess would be they are snowy egrets ( http://en.wikipedia.org/wiki/Egret ). They dark ones might be Eastern Reef Egrets ( http://en.wikipedia.org/wiki/Eastern_Reef_Egret ).