Almost four years ago I received a pair of mute swans as a gift. Supposedly it was a male and a female. They live on a small lake I have on my property and are super happy! The only problem is that they have yet to lay eggs. Could it be that I received two males or two females instead? I understand that a blood test is necessary to determine the sex. If I do that and it turns out the ones I have are the same sex, can I then purchase the opposite sex and introduce them into this environment? I appreciate your help!