First, we need to know what type of aggressive behavior you are describing. Is it actually aggressive or defensive in nature?

Aggressive behavior is one in which the swan chases or attacks other wildlife or people for no apparent reason at any time of the year.

Defensive behavior is one in which the swan chases threats or perceived threats to his territory which is extremely common during mating and nesting season.

This time of the year is the normal mating season for mute swans. So, regardless of the genders, you will still see some defensive behaviors. The swan is clearing its territory for mating and nesting season. Yes, swans of the same gender mate and nest. In same gendered pairs, male swans will not produce eggs, but female swans will produce non-fertile eggs. The male swans are usually the ones which build the nests, but female paired swans will also build nests. The swans will sit on the nests until they realize that no viable young will be produced, the testosterone level for the males will decrease and everything will go back to normal.

Swans are less defensive or aggressive if people and predators leave them alone during the mating and nesting season. Once the hormone levels dissipate, then normal feeding and interaction with people should return. If however, the swans still chase, then you need to look at the reason for this aggression.

Did someone do something to the swan that makes it aggressive, is it particularly aggressive to one particular person or a group of people, i.e., males vs females. Swans may imprint on certain people and they will go out of their way to chase anyone or anything from the area. Yet, they will have nothing to do with anyone other than the person that cares for them. We have had individuals tell us about swans who will literally feed from a female's hands, but her husband cannot get within 2 feet of the bird and vice versa. This even happens with domesticated pets such as dogs and cats.

So, we need to know a little more about the behavior before we can adequately provide you with a possible solution.

We can tell you that even if you tried to pair a female with one of the males, it may not work. This pair has already bonded and it would be inhumane to try and re-pair with a female. You would then have to find another home for the odd man out and again, this could have detrimental effects on both males from losing their mates.

If you choose to have a male and female swan, then you need to find the males a good home so they can stay together.

Having said that, you will need to consider what to do with cygnets should the pair have offspring. You may need a breeder's license to possess an opposite gendered pair. There has been some research in sterilization, but because of its inefficacy, cost, etc., sterilization has not been readily used in swans. Therefore, you will probably have cygnets if a male and female swan is introduced to your habitat. This will bring up a myriad of other problems to include additional veterinary medical costs due to pinioning, care of the cygnets and eventual disposition of the cygnets to a new home. All of this may be ultimately determined by your local wildlife laws. The Regal Swan