**When They're Distant **
Let's use a small flock of mallards as an example. You should begin calling as soon as you can make them out as ducks, as opposed to merely dots in the air. Start with a loud five- to eight-note hail call until they turn. If they don't turn, continue calling until they're out of earshot. If the flock circles from behind or to the side, let them pass, then call again to bring them around. This way, you avoid piquing the birds' interest while they're over the blind, where they may look down and spot you.