Bird enthusiast with warm eggs (8)
I believe the answer is:
nuthatch
'bird' is the definition.
(nuthatch is a kind of bird)
'enthusiast with warm eggs' is the wordplay.
'enthusiast' becomes 'nut' (I've seen this before).
'with warm eggs' becomes 'hatch' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'nut'+'hatch'='NUTHATCH'
Can you help me to learn more?
(Other definitions for nuthatch that I've seen before include "Small songbird often seen on tree trunks" , "Small songbird that climbs up and down trees looking for food" , "Tree-climbing songbird" , "Climbing songbird" , "small bird" .)