Swans will mate throughout the year as a means for bonding between the pairs. Mute Swans will only produce one clutch of eggs each year. This is not the breeding season for them, so they may have been mating for bonding. Mating for egg production usually has eggs being produced within several days to a week after seeing the first mating. Mating will continue to occur with an egg laid every other day until the mother swan has produced her designated number of eggs for that year is reached.

Australian Black Swans mate throughout the year for bonding and will produce 2 clutches a year.

Normally, two species of swans will not produce viable cygnets. There have been cases where interbreeding occurred between species, but humans facilitated the interbreeding. But, in nature this usually does not occur.

Also, female swans without a male partner, will produce non fertile eggs during the nesting/mating season when hormone levels increase. So, the eggs you may be seeing, may not be fertile.The Regal Swan