Crate in dock transported by bird (6)
I believe the answer is:
jalopy
'crate' is the definition.
(I've seen this before)
'dock transported by bird' is the wordplay.
'dock' becomes 'lop' (both can mean to cut).
'transported by' is an insertion indicator (some letters carried or transported by others).
'bird' becomes 'jay' (jay is a kind of bird).
'lop' inserted inside 'jay' is 'JALOPY'.
'in' is the link.
(Other definitions for jalopy that I've seen before include "Old vehicle" , "wreck" , "Dilapidated car (colloq.)" , "A battered old car" , "Old and unreliable car" .)