What goes up must come down, but not in the case of Jack the falcon who decided to break with years of falconry tradition and stay in the sky.

It was a routine part of falconer Rob Allott's act, sending his pair of Lanner falcons Jack and Jill up into the air so they could swoop low above the heads of the crowd at Lanchester Show at the weekend. But while Jill came tumbling down, Jack didn't.

Now his desperate owner is offering a £500 reward for the return of his prize bird, which he has looked after for seven years.

Rob Allott, who runs the Prince Bishops Bird of Prey and Falconry from Belmont in Durham said: "I'm offering this award because this bird is priceless, but only to me. Anyone who has seen Jack and Jill performing will know why he has a big reward on his head. It takes years to train a bird to this standard.

"It feels as if there's a death in the family."

Jack and Jill's acrobatics perform the centrepiece of Rob's show which he conducts from horseback in costume to recreate a medieval hunting scene. Jill has already begun to pine for Jack, as the two birds fly together at every show.

Rob thinks the falcon may have found a thermal of warm air which birds of prey can glide on for up to 30 miles. But a tracking device attached to Jack with a 30 mile radius has produced nothing, even when Rob has taken the device to the top of Durham Cathedral to get the best possible reading.

Rob also fears the falcon may be weak with hunger as Jack does not know how to hunt and may soon start dive bombing people in the hope of being handed food.

The bird is ringed and should still have his silver transmitter and red cap. Anyone who spots him should contact Rob on 0191-3848498.