Without a cry, this bird keeps mum (5)
I believe the answer is:
macaw
'this bird keeps mum' is the definition.
'macaw' can be an answer for 'bird' (macaw is a kind of bird). I am not certain of the rest of the definition.
'without a cry' is the wordplay.
'without' becomes 'ma' (I am not sure about this - if you are sure you should believe this answer much more).
'a cry' becomes 'caw' (caw is a kind of cry).
'ma'+'caw'='MACAW'
Can you help me to learn more?
(Other definitions for macaw that I've seen before include "Long-tailed American parrot" , "Type of parrot" , "Chattering cousin of a cockatoo" , "Largest parrot" , "Tropical parrot" .)