They spent some time splashing around, zooming up and down our pond, practising flying (above and below water).
They are still very much behaving as a flock, all splashing, swimming, or preening together.
a more contemplative moment
And we're now convinced the missing members have merely flown off on their own. The zooming across the pond resulted in some definite flight-like moments, and one of the ducks actually did fly, albeit awkwardly, up out of the pond.