This term apparently describes an odd sounding manoeuvre performed by geese (which would also seem appropriate for a Jabberwock).
When coming in to land, in order to lose height quickly, they tip sideways sometimes flipping over completely.
This I have to see!
See also whiffle.
http://www.travelmanitoba.com/adventure/wildlife/birds.html
http://www.startribune.com/stories/1551/3357159.html