Swans have been pulling a rope in order to ask for bread at Bishop's Palace in Somerset since the 1800s. They have attracted thousands of visitors every year to the palace in Wells.
However, the practice is in jeopardy after the latest pack living on the water parted ways.
Bertie and Vicky were introduced to each other in June, when one of the previous swans died. The pair have been finding it difficult with the bell ringing training after they were reportedly interrupted by a group of ducks.
The male swan has now disappeared, leaving Vicky on her own, and the bell not being rung.
A palace spokesman said: "We can confirm that one of our swans is missing, the male one took to his wings and has taken flight. We have just his female companion now.
"We are hopeful that in fact he will decide the moat is an attractive place to live and return for good. But they are wild swans, they are free to come and go as they please.
"We do care for them, feed them and look after them. But these ones came from a sanctuary and are wild.
''Obviously we would like them to stay but if one wants to fly off we can't stop them. However the female is here still, so we hope her mate will return."
The rope is situated outside a window of the caretaker's sitting room. When heard, the owner feeds the birds outside.
Caretakers Paul and Carol Arblasta explained that Bertie and Vicky didn't seem to understand the system, especially after a group of ducks learned how it worked and began using it.
When the pair did manage to ring the bell, the ducks would quickly emerge to steal all the food.
Paul said: ''These swans are very shy. At first, they didn't even come to the window for a week and a half.
''We tried to train them to ring the bell but the ducks were ringing it instead.
''The swans were left looking bemused cocking their heads, amazed at what they were seeing.''
He added that if Bertie does not return, a new male would be introduced to stop Vicky from being too lonely.
Conveyancer Marianne Smith has launched an unofficial 'swan watch' to find Bertie.
She said: "We've been hoping the separation isn't permanent."