Bird to emerge from shell, head first (8)
I believe the answer is:
nuthatch
'bird' is the definition.
(nuthatch is a kind of bird)
'emerge from shell head first' is the wordplay.
'emerge from shell' becomes 'hatch' (I've seen this before).
'head' becomes 'nut' (informal term for somebody's head).
'first' says to put letters next to each other.
'hatch' after 'nut' is 'NUTHATCH'.
'to' is the link.
(Other definitions for nuthatch that I've seen before include "warbler?" , "Small songbird that climbs up and down trees looking for food" , "Songbird named from its penchant for a kind of fruit" , "Flier" , "Trunk-climbing bird" .)