Flier appears to steal in (5)
I believe the answer is:
robin
'flier' is the definition.
(robin is a kind of birdanimal)
'to steal in' is the wordplay.
'to steal' becomes 'rob' (robbing is a kind of stealing).
'rob'+'in'='ROBIN'
'appears' is the link.
(Other definitions for robin that I've seen before include "Batman and --" , "See 7" , "Traditional Christmas card bird" , "Garden bird" , "Christmas-card bird" .)