LONDON (AP) — The annual count of swans belonging to Queen Elizabeth II has begun on the River Thames.

The five-day event known as Swan Upping dates back to the 12th Century and began as a ritual to ensure there were enough swans for feasting. Now it is more about conservation.

The British monarch traditionally claims ownership of all unmarked swans in open water.

Swan Uppers — a team of dedicated boat men — are tasked with finding swans on a specific stretch of the River Thames. When a group of cygnets is spotted, they cry "All Up" then mark the young birds and check them for disease or injury.

David Barber, the queen's official Swan Marker, hopes the event will draw attention to the threats young swans face on the river.