Queen's swans
Swans and cygnets are weighed, measured, inspected and recorded in the annual counting of The Queen's swans, known as 'Swan Upping', along the River Thames near Chertsey in July 2015. Reuters

Scientists are testing seven dead swans from the Queen's flock over concerns that they were killed by bird flu. The H5N6 avian influenza is believed to have caused the deaths and experts are checking to make sure that the virus won't spread, the Sun reported.

A source at the Department for Environment, Food & Rural Affairs (Defra) told the Sun: "Bird flu is feared to have struck the Windsor swan flock.

"They are waiting for the tests to come back but everyone suspects the worst. The results are expected early next week."

Regarding the deaths of the seven swans, a tenth of the total number, the royal biographer Penny Junor told the paper: "The Queen will be profoundly upset about this. She is an animal lover and if they have bird flu it's horrible."

The Queen's official Swan Marker David Barber, who carries out an annual census of Thames swans said: "We are deeply saddened by the loss."

In the annual census, known as "swan upping", it was found there were 72 swans at Windsor. Bird flu has also killed wildfowl earlier in the year at Amwell Nature Reserve in Hertfordshire and one in Abbotsbury Swannery in Dorset last year.

Defra said the latest outbreak would be unlikely to lead to a cull, saying that would only happen if bird flu entered the food chain, the Sun reported.