Flier's welcome in Royal Navy (5)
I believe the answer is:
raven
'flier's' is the definition.
(raven is a kind of birdanimal)
'welcome in royal navy' is the wordplay.
'welcome' becomes 'ave' (I've seen this before).
'in' indicates putting letters inside.
'royal navy' becomes 'rn'.
'ave' inserted within 'rn' is 'RAVEN'.
(Other definitions for raven that I've seen before include "Big black bird" , "Glossy black colour" , "Species of crow" , "Large bird of the crow family" , "Black crow" .)