If these swans have never mated in 4 years, it would seem that you have two males instead of a mating pair. Some breeders sell swans based upon cloacal checking instead of the more reliable DNA Sequencing. Cloacal checking is not reliable, especially at a young age because the genitalia are not as developed until later, so what you think you have may not be a reality which will show up during mating season. First, you need to have the gender verified for both swans through DNA Sequencing which can be conducted by a veterinarian.
Once verified, you have several options. If both males and aggressive behavior does not settle after a couple of weeks due to hormones, then you need to keep them separated on the pond ( must allow water and food access to both at same time only separated so that one does not become king of the pond– you can also remove both from the pond at the same time and move indoors- separated but within sight range) Indoor separation will require safe enclosure from any predators climbing in or digging under, clean food daily and using straw so no abrasive substrate (flooring). After couple of days, reintroduce both swans to pond, monitor closely and see if aggression continues.
1. If aggression continues, you need to find a good safe home for one of the swans and allow the remaining swan to live its life alone- males will do fine on their own.
2. Trade out both swans for a pair of mating swans- would recomnend not going back to sane breeder if they gave you wrong gender at the time of sale of these swans because you can possibly have a recurrence of wrong i.d. If there is a possibility of trading one or both swans, would recommend you contact Bob Knox- 847-875-3947.
3. If you are looking for breeding pair of Mute Swans, you may need to check on your state laws. Many states are killing Mute Swans and will not allow you to have any Mute Swans, much less a breeding pair. Should you have a breeding pair, you may need a license for possession and a breeding license since you will need to find a good safe home for all cygnets once the next mating season occurs as the parents will chase them from the pond. All cygnets must be pinioned (rendered unable to fly at 1-2 weeks of age by a reputable avian veterinarian).
Mute Swans can produce 1-12 cygnets annually, which means you will have the pinioning and rehoming issue every year. It is for this reason, that we strongly urge you find out the gender of your swans, rehome one if the aggression does not work out or trade out both swans for 2 females( non-breeding). Female swans will get along with other females, especially if they are raised together at young age, unlike males which usually not accept another male unless they are siblings, and even then may not get along.
Swans will mate with each other regardless of gender if the same genders are raised together. Males (if they do get along, will mate, construct a nest but obviously produce no eggs). Females will mate with each other, build a nest and produce eggs- but obviously will not produce young.
We think you have two males and each are trying to establish dominance during a heightened hormonal mating season. This may resolve itself once hormone levels go back to normal- several days to a week.
Unscrupulous breeders sell swans without notifying potential buyers of state laws and requirements of raising and breeding swans, or will sell same gender swans without doing diligent sequencing or knowingly passing off same gendered swans or sick swans so they can make a sale. Always do your homework and do background checks on breeders, ask for veterinarian or other certified health/gender documentation and inquire about warranty on bill of sales if something goes wrong. We hope this information is of benefit. The Regal Swan