SWAN killers and the worst floods in living memory have left the regal creatures in the grip of a population crisis.

David Barber, the Queen's Swan Marker, has warned that the population could have dropped by as much as 30 per cent following reports of stonings by youths up and down the Thames.

Flooding also forced many swans to nest away from their usual spots leaving them exposed and vulnerable.

Mr Barber, based in Cookham, is responsible for maintaining the Queen's swans and leads the historic annual Swan Upping which travels up the Thames in July logging the number of newborns.

He said: "We are concerned by the increased vandalism by youths. Year after year there are a few more. Just here in Cookham we had reports of youths throwing stones at a nest but by the time we got there it was too late. There were seven in the nest and now there are just four."

Last summer a swan was shot through the head with an air rifle near Lock Island in Marlow.

And Mr Barber reported two swans had recently been clubbed to death with sticks in Windsor.

He said the drop in numbers would show up in two or three years time when people notice a downfall in the number of swans on the river but he said the population should recover next year.

Swan Upping begins on July 16 in Sunbury, near Chertsey, and arrives in Marlow on July 18.