A) Carrions and magpies become communal birds in the autumn and winter, and crows, in particular, may be seen in large communal roosts. In February, dominant crows break away from the community to pair up and defend a territory. It is worth remembering that the major predator of crows eggs and young is other crows. The best results with a Larsen trap will be achieved when the trap is placed within the territory of a pair of crows or magpies as they will then try to attack and drive off the call bird.
Though the spring catching period is not exclusive, it is the most productive time and I never set traps outside this peak period. You could perhaps tempt the odd inquisitive bird in the winter by putting the traps out of sight for some time or by moving them. As winter sets in and food becomes scarce, you might lure a crow or magpie, or even a fox. I caught a mangy fox in a Larsen trap some years ago.