A Larsen trap is a device used to live trap wild birds. It is used in avian predator control programs, and in scientific research.
It is essentially a cage with two (or more) compartments. A previously caught magpie or crow is kept in the decoy compartment, and this attracts territory holders who see the decoy as an intruder.
Alternatively create a ”nest” in the decoy compartment or use a decoy magpie.
Use in the United Kingdom
The Larsen trap is legal to use under general licence. It is the most widely used magpie population control method amongst gamekeepers and conservationists. It is also used to trap magpies by back-yard conservationists concerned for the well being of nesting song-birds.
The decoy bird must be properly cared for according to local regulations.In 2003 the RSPCA successfully appealed an acquittal of a case in which a single decoy magpie was used throughout the summer in a cage which was too small for the bird to stretch its wings, contrary to the Wildlife and Countryside Act.