Bird dropping first of eggs in the long grass (6)
I believe the answer is:
thrush
'bird' is the definition.
(thrush is a kind of bird)
'long grass' is the wordplay.
'long' becomes 'th' (I can't justify this - if you can you should believe this answer much more).
'grass' becomes 'rush' (I've seen this before).
'th'+'rush'='THRUSH'
'dropping first of eggs in the' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for thrush that I've seen before include "Speckle-breasted songbird" , "sprue" , "Speckled songbird or throat infection" , "Infection of the mouth and throat" , "Common songbird or throat infection" .)