Nah that's bollocks mate.
An extract from the Defra website
Ladder traps
These traps were originally devised by MAFF and although still in use are not as popular as the Larsen. The trap is normally about 12 feet square and about 6 feet high. The roof of the trap is the shape of a flat bottom 'V', the flat part being formed by the ladder. This has rungs approximately nine inches apart, which allow birds, (mainly crows), to enter the trap but prevents them from getting back out. The more that enter the trap, the more effective it becomes. These traps are normally baited with grain, d