Pigeon perch (5)
I believe this is a double definition.
'pigeon' is the first definition.
(both can mean an informant)
'perch' is the second definition.
(Other definitions for stool that I've seen before include "place butt on one?" , "Motion" , "Small seat" , "Seat without a back" , "Simple seat" .)
'pigeon perch' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ledge that I've seen before include "Mantelpiece" , "Narrow projection or shelf" , "Shelf-life projection" , "A step" , "Ridge or shelf" .)