Second means of identifying male animal (4)
I believe the answer is:
stag
'male animal' is the definition.
(I've seen this in another clue)
'second means of' is the wordplay.
'second' becomes 's' (common abbreviation).
'means of' becomes 'tag' (I can't justify this - if you can you should give a lot more credence to this answer).
's'+'tag'='STAG'
'identifying' acts as a link.
Can you help me to learn more?
(Other definitions for stag that I've seen before include "in a rut, perhaps?" , "Stock market speculator" , "Investor" , "Male animal" , "Adult male deer, often with antlers" .)