Inside, they are, I hear, on one early eucalypt to hold a nest (5)
I believe the answer is:
eyrie
'a nest' is the definition.
(I know that eyrie is a type of bird nest)
'inside they are i hear on one early eucalypt to hold' is the wordplay.
I cannot really understand how this works, but
'i' is found in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found in the leftover letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for eyrie that I've seen before include "retreat for hunter" , "elevated position" , "High altitude habitation" , "Eagle's lair" , "Inaccessible place" .)