Scientists from the Department for Environment, Food and Rural Affairs (Defra) are currently investigating the suspected case of H5N6 avian influenza, according to reports.
David Barber, the Queen’s official Swan Marker, who is responsible for the 800-year tradition of carrying out an annual census of Thames swans, said in a statement: “Over 20 swans have died now and there’s a lot which are seriously ill which will die — well over 20 more.”
Defra confirmed that seven of the swans that died were currently being tested for bird flu.
“We are deeply saddened by the loss of these swans,” Barber continued. “We’re waiting to hear from Defra, but yes it is bird flu. I’m sure the Queen would be concerned. You cannot do anything about it. It will burn itself out. They’re wild birds and it is spread by wild birds and we’ve been very unlucky.”
According to Defra, the outbreak at Windsor, where Prince Harry and Meghan Markle will tie the knot on May 19, is unlikely to lead to a cull (selective slaughter). “There’d only be a cull if it’s a bird involved in the food chain, poultry for example,” they said in a statement.
The Queen, who is a known animal lover, takes great interest in the Windsor swans.
The Crown owns all mute swans (the most common of three local species) found on open water in the U.K. as part of a tradition dating back to the 12th century. Each year, a Swan Upping takes places in which the animals are weighed and measured.
According to the official British Monarchy website: “The swans are also given a health check and ringed with individual identification numbers by The Queen’s Swan Warden. The swans are then set free again.”
After the Swan Upping has been completed every July, the Queen’s Swan Marker releases a report that provides data about the number of all swans that were accounted for.
This article originally appeared on PEOPLE.