Putting down any bird or animal is never easy. Even an old rooster like myself, you has taken over 200 deer, shot countless duck, peasants, turkeys, and dove, finds the task objectionable. However, so times it is the only option. Probably the least messy and humane method would be a cervical dislocation.
Assuming you don't have great hand strength I would recommend using the "cheat" method. Hold the bird upsided down by the feet and in a few moments it will lose consciousness. While still holding the feet place bird on ground with a board across its neck.Stand on both ends. Pull upward until you feel neck separate.
Assuming you don't have great hand strength I would recommend using the "cheat" method. Hold the bird upsided down by the feet and in a few moments it will lose consciousness. While still holding the feet place bird on ground with a board across its neck.Stand on both ends. Pull upward until you feel neck separate.