Here are a few articles that help identify the predator. It’s not always easy.
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2111/ANSI-8204web.pdf
http://www.extension.org/pages/71204/predator-management-for-small-and-backyard-poultry-flocks#.VDQPcxEtCUk...