Crossword Genius

Cry when husband leaves for a fly-by-night? (3)

Ross

I believe the answer is:

owl

'a fly-by-night?' is the definition.
(creature which flies at night)

I don't understand how the remainder of the clue works.

(Other definitions for owl that I've seen before include "eg Snowy, Tawny" , "One flying" , "Nightbird" , "Member of Parliament" , "Winged hooter" .)

I've seen this clue in The Times.
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