What is this behavior?

[sourland]

All Drakes do that. He's impressing the ladies..

It very well may be a mating/posturing display. It's something I have puzzled over for quite some time.

 

[Miss Lydia]

My young Runner does it then bends over and runs around for a sec.

 

[Thunderduck9]

My ducks do that after mating one of the lady’s then they run around with there head to the ground its hysterical