The happy couple at Abbotsbury Swannery are the only homosexual swans among more than 1,000 birds at the reserve.
They are believed to be only the second male pair ever to hook up at the reserve.
The pair show no interest in their female companions and only have eyes for each other.
Dave Wheeler, from the swannery, said: "The two birds both hatched in 2002 and are sort of together.
"They have been together for several nesting seasons and basically keep territory as if they are a nesting pair."
The twosome flock together at the start of the nesting season in March and perform rituals associated with a breeding couple.
Manager of Abbotsbury Swannery, John Houston, said: "The swans have been nesting together like this for several years and they get together every nesting season and form a nest together.
"They sit on the nest and act in every way as if they were a pair expecting to lay eggs.
"It is quite sweet."
Like most couples, the swans are known for the occasional lover's tiff, but are quick to sort out their differences.
"They just always stay together and I hear that they have some spectacular fights with each other, but they always make up and get back together," said Mr Houston.
"We have more than a thousand swans here in the reserve and they are the only two doing this. We don't know of any others acting in this way in the area.
"We realised they were together because the swan herds can obviously tell the difference between the males and females as the cobs have a much larger bump on their nose.
"They are sexed and tagged at birth so we know from their rings that they are both male."
Records for the swannery date back to 1393 and it is believed that they are the only pair of homosexual swans currently nesting at the reserve.
Homosexual behaviour is universal across the animal kingdom, from whales to snails and even nematode worms.
