Night birds (4)
I believe the answer is:
owls
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">night birds</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for owls that I've seen before include "Slow kind of birds" , "Slow sort of birds" , "Members of Parliament" , "Nocturnal birds" , "Strigiform creatures" .)