Headless Black bird

I sadly came across a dead blackbird at the bottom of a hedge in my garden this morning, it had no head and another wound at the nape of its neck.  Until 3 days ago I had regularly seen around 6 blackbirds feeding in my back yard both male and female, when I noticed ALL my visiting birds only here in small numbers, and no Blackbirds.  What is going on? and what could have killed my bird? I live on open farm land.