Yellow egg to lift across log for bird expert (13)
I believe the answer is:
ornithologist
'bird expert' is the definition.
(I've seen this before)
'yellow egg to lift across log' is the wordplay.
'yellow' becomes 'or' (heraldic term).
'egg' becomes 'nit' (a nit is an insect egg).
'to' means one lot of letters go next to another.
'lift' becomes 'hoist' (hoist can mean to lift something up).
'across' is an insertion indicator.
'hoist' enclosing 'log' is 'hologist'.
'or'+'nit'+'hologist'='ORNITHOLOGIST'
'for' acts as a link.
(Other definitions for ornithologist that I've seen before include "Student of birds" , "Person who studies birds" , "Iron's too light (anag.)" , "Studier of birds" , "Bird expert" .)