I think the 7 letter bird has a large bill david if i am on the right lines... then change the last 3 letters to the opposite ..in fact just adding a letter gives the opposite.
Seems to parse but I may weel be wrong!
21a is normal I think .. an anagram
25a also a normal clue that i got early on
19a a liqueur minus 2 letters gives you the "seeds"
Hopefully you can progress a bit now!