I think it's more they are aware of things that are not natural to them or out of place, movement the wrong color may make a duck or goose more aware especially later in the season.

Here where I hunt it is just out side the city and 1 of our blinds is within 1000 yards of a marina so the ducks and Geese are use to boats, I have had Geese land in my Decoys and swim behind my blind and right up to the boat that is tied off to the blind, not until I moved did they become alarmed and left.

I have seen Black Ducks fly towards a blind and shoot straight up and over just like he knew the range at which a shotgun would travel and avoided it.

If you are in a blind or in a situation where you and a hunting partner are camoed walk away from where he/she is and have them move there head and watch how their face stands out, of course the whiter someone is the more it stands out. Just imagine what a duck is seeing when flying over looking down

So my take on it is that they are aware of things and movement that are not natural to their surroundings, they become wise to blind locations and for the Hail call it is just used for ducks at long distance hoping that the duck will hear 1 or 2 notes and come in your direction.