Voracious bird round United States (8)
I believe the answer is:
ravenous
'voracious' is the definition.
(I know that voracious can be written as ravenous)
'bird round united states' is the wordplay.
'bird' becomes 'raven' (raven is a kind of bird).
'round' becomes 'o' (o is a circular letter).
'united states' becomes 'US' (abbreviation for the United States).
'raven'+'o'+'us'='RAVENOUS'
(Other definitions for ravenous that I've seen before include "starved?" , "Extremely hungry" , "Really hungry, starving" , "Wolfish" , "Famished" .)