Migratory bird (6)
(Other definitions for cuckoo that I've seen before include "Bird (with a bad reputation)" , "building no nest?" , "flier?" , "counting as bird? Yes and no" , "Bats" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">migratory bird</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tern that I've seen before include "Winger" , "Pay rent for seabird" , "Fork-tailed relative of the gull" , "Fork-tailed seabird" , "Three-masted schooner" .)