What bird kills blue jays and not eating them hangs them upside down?

Answer 1

Shrikes, (also called "butcher birds") will hang insects and small rodents this way on thorns or barbed wire, but a jay is too large for the shrike to tackle, being somewhat larger than either the loggerhead or northern shrike. This sounds to me like a human activity. Corvids like jays and crows are often killed and hung to frighten other members of their species away from an area.