Mandarin/ Carolina M

[Hawk2099]

Hi I really need advice last year I got mandarin duck female an male this year I got female an male Carolina ducks but my male has paired with my female mandarin an my mandarin male has paired with my female Carolina how do I stop this from happening or is it too late to stop it an on some pages I see that mandarin pair for life other sites say they change there partner every year so this has confused me