Really stange bird deaths?

We usually find dead birds (mostly small finches) around but lately, the dead birds all are in the same weird condition. They are all missing their heads. There is nothing else missing from the birds, just their head. There are no signs of struggle around the birds (feathers, blood etc.). Also, no heads have ever been found. What could possibly be decapitating all these birds and is there anything we can do about it?