Bird showing split crest (9)
I believe the answer is:
partridge
'bird' is the definition.
(partridge is a kind of bird)
'split crest' is the wordplay.
'split' becomes 'part' ('part' can be a synonym of 'split').
'crest' becomes 'ridge' (I've seen this before).
'part'+'ridge'='PARTRIDGE'
'showing' is the link.
(Other definitions for partridge that I've seen before include "Widespread bird" , "Flighty type" , "early Christmas present" , "Game bird (in a pear tree?)" , "Flier" .)