There may be something more general in your theory
but in the precise terms stated it doesn't hold. For instance, Procellariiformes
can fly with the feet exposed and trailing or with the feet hidden, tucked
forwards into the belly feathers. Both strategies are shown in the photo of two
Black-winged Petrels in Seabirds in the National Photographic Index (p.
226). See also p. 165. The feet are not concealed in the undertail coverts
because in some species they extend beyond the tail when
'trailed'.
Mike Carter 30 Canadian Bay Road Mt
Eliza Vic 3930 03 9787 7136
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