I recently read Mike Tomkies' A Last Wild PLace, his account of ten years
near an isolated loch in western Scotland. He observed a bird--can I
remember which one? of course not--also reputedly unable to walk, but
which scooted itself along pretty well on its chest/bag legs
(wheelbarrow? John Cleese silly walk?). It used this walk only to cross
the short way to its nesting site.

Anyway, the "walkless" grebes might have the same ability for short
distances. I recall Tomkies was quite surprised and delighted to see the
bird walk, because all experts agreed it couldn't.