Worm initially grabbed by unhealthy-looking bird (7)
I believe the answer is:
swallow
'bird' is the definition.
(swallow is a kind of bird)
'worm initially grabbed by unhealthy-looking' is the wordplay.
'initially' says to take the initial letters.
'grabbed by' means one lot of letters goes inside another (inserted letters are grabbed inside).
'unhealthy looking' becomes 'sallow' (I've seen this in another clue).
The first letter of 'worm' is 'w'.
'w' put within 'sallow' is 'SWALLOW'.
(Other definitions for swallow that I've seen before include "Ingest - bird" , "Songbird" , "Get down" , "One with wings" , "Eat - bird - believe" .)