I can't quite work out the trigger mechanism - but I assume that there is a nail or something on that perch just hooking the door and holding it against the tension of the spring.
Has the trap fired at all ? or just had no interest ?
Try a rabbit with the guts still present and half out of the body, that often attracts crows quicker.
There is also persistent rumour that crows prefer side entry traps where as magpies catch better in top entry.
the pirtch has a grove in it holding the door opern witch props as son as any think lands on it has been trigerd a cup time but buy smal