In pictures: Swan Upping begins on Thames

The historic Swan Upping ceremony is the annual census of the swan population on the Thames. Credit: Steve Parsons/PA Wire
A team of boatmen called Swan Uppers have the job of catching and marking the birds between Sunbury-on-Thames and Abingdon Credit: Steve Parsons/PA Wire
The Queen's Swan Marker and the Royal Swan Uppers use six traditional Thames rowing skiffs to weigh and measure cygnets Credit: Steve Parsons/PA Wire
The ritual known as Swan Upping dates back to the 12th century Credit: Steve Parsons/PA Wire
It began when the ownership of all unmarked mute swans in open water was claimed by the Crown in order to ensure a ready supply for feasts. Credit: Steve Parsons/PA Wire
When a brood of cygnets is sighted, a cry of "All up" is made to signal that the boats should get into position. Credit: Steve Parsons/PA Wire