According to
@Magnolia Ducks the drakes say "vent, vent, vent…" all day long, referring to their favorite part of the female duck's body.
I'm not so sure about that…
First they seem not to repeat the same word over and over again, but rasp very accordingly to the actual situation:
- Their attached female duck(s) are foraging and there is no threat insight: A gentle, calming "rasp, rasp, raaaasssp" - as if to inform the ladies that they are safe
- Something suspicious appears in the sky: Sudden silence, drake is observing, ducks stop foraging looking at "their" drake and observing the sky themselves.
- Another drake dares to approach: Bursts of short rasps, getting louder and louder with every "rasp", in the end both drakes standing chest to chest and whoever can rasp louder and/or(?) faster wins.
- HillBilly comes outside: Everydrake starts ton rasp as loud and as fast as they can to alert the ducks. - Cat-food is in reach!