Bird-feeder filler (5)
I believe the answer is:
seeds
'bird-feeder filler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for seeds that I've seen before include "Favoured entrants in a knock-out competition" , "Pips" , "Initiates the growth of" , "top tennis players" , "favourites for the trophy?" .)