A Serial Murder of Crows

We currently have 100+ crows & jackdaws in our village. They flock together early morning and evening and I normally am not bothered to see their arrival to my garden however they have started a murderous rampage in my garden and after finding a few dead sparrows and a fledgling blackbird with horrible injuries to its back and neck I checked my home security to find a jackdaw jumping onto one of the sparrows and pecking it to death then leaving the body, this has happened twice before and I am now concerned for the songbirds and little fledglings as the crows and jackdaws have started roosting in the garden trees. 
The smaller birds are not taken for food for young or even being targeted, it just seems that they are attacked at random, could anyone tell me why would the jackdaw just kill the birds this way and for what purpose? Is there anything I can do to protect the smaller birds or do I have to accept that the crows and jackdaws are now here to stay and the smaller birds will leave or be killed