Pigeon in front of railing (5)
I believe the answer is:
homer
'pigeon' is the definition.
(homer is a kind of pigeon)
'in front of railing' is the wordplay.
'in' becomes 'home' ('he's in' can mean 'he's home').
'front of' says to take the initial letters.
The initial letter of 'railing' is 'r'.
'home'+'r'='HOMER'
(Other definitions for homer that I've seen before include "Great Greek author of The Iliad" , "Greek poet, c. 800 BC" , "Great Greek who wrote The Iliad" , "Measure < of poet's" , "makes round trip by air" .)