Of birds (5)
I believe the answer is:
avian
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">of birds</span>' is the definition.<br/ ><span class="explanation-format__explanation">(avian means relating to birds)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for avian that I've seen before include "Relating to birds" , "Lizard with adhesive foot-pads" , "Like a booby" , "Pertaining to or characteristic of birds" , "Regarding birds" .)