Wild hares resembling ostriches! (5)
I believe the answer is:
rheas
'ostriches' is the definition.
The answer and definition can be both animals as well as being plural nouns.
Maybe you can see an association between them that I can't see?
'wild hares' is the wordplay.
'wild' indicates an anagram.
'hares' anagrammed gives 'RHEAS'.
'resembling' acts as a link.
Can you help me to learn more?
(Other definitions for rheas that I've seen before include "these birds won't fly" , "Ostrich-like birds" , "Flightless birds" .)