King Charles Owns All Unmarked Swans, and They Were Just Counted in Swan Upping Tradition

King Charles has several royal titles, including the "Seigneur of the Swans."

Since the 12th century, the British crown held the right to claim ownership of all unmarked mute swans swimming in open waters throughout the U.K. The Royal Swan Marker, currently David Barber, sets out with a team every July for an ancient tradition known as Swan Upping, the annual census of the swan population on the River Thames focused on a 79-mile stretch from Sunbury-on-Thames to Abingdon.

On July 19, King Charles' team shared a video of this year's five-day event on the royal family's official social media pages. The footage showed the Swan Upping team hitting the water in traditional skiffs featuring flags, oars and more carrying King Charles' royal cypher to designate that they're working on behalf of the monarch.

"The annual Swan Upping on the River Thames concluded today," they captioned the post. "The week-long flotilla of traditional Thames rowing boats (called 'skiffs') record the census and health of the swan population over a 130-km route."

Barber sported a red jacket with a patch designating him as "His Majesty's Swan Marker" and a cap featuring a white feather for the occasion.

While British monarchs historically used their right to cook and eat the birds at extravagant royal feasts, the practice of Swan Upping now focuses on conservation and education.

As Swan Uppers come across a family of swans with cygnets (young swans), someone shouts, "All up," and the crew corrals the birds so they can lift them out of the water. The swans and cygnets have their feet or wings tied before they are moved onto the riverbank to be weighed, measured and inspected for signs of illness or injury, often caused by fishing hooks and lines.

Barber previously told PEOPLE, "The whole process, as long as there's no serious injury on the swans, takes about 20 minutes. All the young cygnets and adult birds have to be released together as the cygnets will get lost otherwise. So you have to be very, very careful. You face the cygnet to the parent bird, and then they will go off in the water together."

Although it's a short process, it can be tricky. "Swans are large birds that weigh up to 15 kilograms [33 pounds]," Barber explained. "They have a wingspan of approximately 2.5 meters [8.2 feet], so they are a very large bird to deal with. They are heavy to get out of the water and, of course, they flap around quite a bit too."

“It's worth doing because if we didn't, the population of swans would just gradually disappear,” the Swan Marker added.

In recent years, the Swan Upping census found a "considerable downturn in cygnet numbers due to the loss of many of the breeding pairs during the outbreak of Avian Influenza," according to the Swan Marker's website.

"In 2023, the number of cygnets weighed, measured and given a health check between Sunbury on Thames and Abingdon Bridge was 94 compared to 155 in 2022. This disappointing downturn in numbers was anticipated due to the severity of the outbreak of Avian Influenza in Autumn/Winter 2022 that caused the deaths of many thousands of swans throughout the country, and many hundreds on the River Thames," they continued. "In spite of these extraordinarily difficult circumstances, we were pleased to note the majority of cygnets that were given a health check were in very good condition."

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No members of the royal family attended this July's Swan Upping process, as is the case most years, but there was a very special guest at the event in 2009: then-Seigneur of the Swans, Queen Elizabeth.

"The Queen visited swan upping in 2009," Barber told PEOPLE. "She came along and was very interested in all the processes that we were doing. Asked lots of questions. Met lots of children."

Princess Anne also checked it out in 2018, and Barber recalled, "She actually went in my rowing skiff and sat next to me as we rowed up the river. She took a lot of interest in it all."