The greeting call is a series of single quacks, sounds easy enough, right?
In this video you'll learn how to do the greeting call, which is a combination of single quacks. If you don't know how to do a single quack, you'll want to look that up first.
You want to do the greeting call when the ducks are close enough to hear you without effort, and the cadence is key. The greeting call has five notes, and is five single quacks combined.
Did you hear how he "cut off" each single quack? This made it so the sounds were more decipherable and in general made the call most natural sounding.
Here's a good tip to remember this call, simply think, "Three blind mice, quack, quack." Now that you know how to do this call, get out there and practice; it's the only way you'll get better.