Bird some ornithologists wanted (4)
I believe the answer is:
swan
'bird' is the definition.
(swan is a kind of bird)
'some ornithologists wanted' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'SWAN' can be found hidden inside 'ornithologists wanted'.
(Other definitions for swan that I've seen before include "Stately aquatic bird" , "Large, long-necked bird" , "Large aquatic bird" , "Whooper, perhaps" , "Flighty" .)