Bird little upset being eaten by quarry? (6)
I believe the answer is:
peewit
'bird' is the definition.
(peewit is a kind of bird)
'little upset being eaten by quarry?' is the wordplay.
'little' becomes 'wee' (similar in meaning).
'upset' says the letters should be written backwards.
'being eaten by' means one lot of letters goes inside another.
'quarry?' becomes 'pit' ('pit' can be a synonym of 'quarry').
'wee' back-to-front is 'eew'.
'eew' inserted inside 'pit' is 'PEEWIT'.
(Other definitions for peewit that I've seen before include "Lapwing turned up in a wee pit" , "Kind of plover; let it weep" , "Lapwing - ie wept (anag)" , "Does it weep, this bird?" , "Flighty type" .)