Most severe, transporting rest home (8)
I believe the answer is:
sternest
'most severe' is the definition.
(I've seen this in another clue)
'transporting rest home' is the wordplay.
'transporting' indicates anagramming the letters (I've seen 'transported' mean this).
'home' becomes 'nest' (a bird's home).
'rest' is an anagram of 'ster'.
'ster'+'nest'='STERNEST'
(Other definitions for sternest that I've seen before include "Most strict and demanding" , "Most serious and unrelenting" , "Strictest or grimmest" , "Most unfriendly" , "Most severe and unrelenting" .)