In pictures: Annual swan upping census carried out

The annual tradition of counting swans on the River Thames has got under way.

The count - known as swan upping - is the royal census of birds on the river and dates back to the 12th century.

It is designed to give an idea of the health of their population, and is carried out every July.

It began at Sunbury Lock in Middlesex on Monday and will finish at Abingdon Bridge, Oxfordshire, on Friday, passing through a number of places including Henley, Sonning and Caversham.

This year's swan marker, David Barber, said the previous two counts had shown a "downturn" in cygnet numbers as a result of bird flu.

"Fortunately, there has been a decrease in reported cases of the disease in the River Thames area in recent months," he said.

"Calmer river conditions of recent weeks will also benefit young cygnets as they learn to navigate the waterways with their parents."

After the event, he will produce an annual report with the results.