Bird turned up covered with special foam (5)
I believe the answer is:
spume
'foam' is the definition.
(spume is a kind of foam)
'bird turned up covered with special' is the wordplay.
'bird' becomes 'emu' (emu is a kind of bird).
'turned up' says the letters should be written backwards.
'covered with' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'special' becomes 'sp'.
'emu' reversed gives 'ume'.
'ume' after 'sp' is 'SPUME'.
(Other definitions for spume that I've seen before include "Surf" , "Froth on waves" , "Foam on waves" , "Sea foam, froth" .)