Sadists who crucified, beheaded and hung a rare swan on a tree are thought to have been carrying out a sick pagan ritual.

Horrified staff at a Durham Wildlife Trust nature reserve discovered the gory remains of the mute swan at their special site of scientific interest at Houghton-le-Spring on Thursday.

The swan was decapitated and hung up on an elder tree - said to be a significant species to ancient pagan witches - after being killed with a crossbow.

It is thought the sick stunt forms part of an ancient sacrifice once common around Halloween.

Terry Coult, Durham Wildlife Trust's conservation manager, said staff were visibly upset after making the discovery in an isolated copse at Joe's Pond, at Rainton Meadows.

He said: "It was crucified and hung up in the tree. Its head was removed and its wings were spread out. It seems like someone was trying to make a point.

"Whoever did this obviously went to some lengths - they had gone to the trouble of threading the branches of the tree through it.

"The interesting thing is that it was hung up on an elder tree close to Halloween. This particular tree used to be known as the witches' tree in the North-East.

"It's not unusual for people to trespass and take potshots at the swans, but this is something else."

This latest killing follows the slaughter of 80 rare kitti-wakes at a coastal beauty spot in South Tyneside in the summer.

In a chilling incident also linked to the occult, the dead birds were laid out to spell the word "death".

Northumbria Police said the swan - which is Britain's largest bird - is a protected species under the Wildlife and Countryside Act of 1981.

A force spokesman appealed for information to help catch the culprits.

Anyone who can help the investigation should contact Houghton-le-Spring police on 0191-454 7555