Bird ascending east German mountain (5)
I believe the answer is:
grebe
'bird' is the definition.
(type of bird)
'ascending east german mountain' is the wordplay.
'ascending' says the letters should be written in reverse.
'east german' becomes 'e' (I can't explain this - if you can you should give a lot more credence to this answer).
'mountain' becomes 'berg' (I've seen this before).
'e'+'berg'='eberg'
'eberg' in reverse letter order is 'GREBE'.
Can you help me to learn more?
(Other definitions for grebe that I've seen before include "Swimmer" , "I'll dive in" , "Small diving waterfowl with a long neck" , "Diving bird which may be crested" , "Freshwater diving bird" .)