[1] : The Collaborative International Dictionary of English v.0.48

nightbird \nightbird\ n.
   a person who likes to be active late at night; a night owl.

   syn: night owl, nighthawk.
        wordnet 1.5
see also:
night owl 

[2] : The Collaborative International Dictionary of English v.0.48

nighthawk \nighthawk\ n.
   1. a person who likes to be active late at night; a night
      owl.

   syn: night owl, nightbird.
        wordnet 1.5

   2. zool. any of several mainly nocturnal north american
      goatsuckers, especially chordeiles minor, or the related
      european goatsucker caprimulgus europaeus, also called
      the nightjar.

   syn: bullbat, mosquito hawk.
        wordnet 1.5
see also:
night owl chordeiles minor caprimulgus europaeus 

[3] : The Collaborative International Dictionary of English v.0.48

night owl \night" owl`\ n.
   a person who likes to be active late at night.

   syn: nighthawk, nightbird.
        wordnet 1.5

[4] : WordNet (r) 2.0

night owl
     n : a person who likes to be active late at night syn: nighthawk,
          nightbird
see also:
nighthawk nightbird 

Barn Owl >> B Words
Barn Owl, definition of term: Barn Owl
barn+owl_pag1.html