Whiffling[1] is a term used in ornithology, describing the action of descending rapidly from a height once the decision to land has been made, involving fast side-slipping first one way and then the other. The term is usually applied to geese (family Anatidae), whose flocks whiffle spectacularly, especially when wishing to avoid a long, slow descent over an area where wildfowling is practised
It results in an aerial maneuver in which a bird flies with its neck twisted 180 degrees and its body upside down in order to achieve a rapid yet controlled descent.