I also believe you're jumping to the wrong conclusion.
It seems unlikely that someone would come open the gate and then stand around until the ducks made their way out then shut the gate and leave.
At that time of night I could open my gate and it would take hours if at all that they would get up and find the open gate and leave.
The only scenario involving a human I could see was someone going in the yard and catching them and leaving with them.
If I was to jump to conclusions I would say something like foxes hopped your fence grabbed them and left. Foxes hardly ever leave clues behind and one or two of them will snag a bird take it a safe distance then repeat several times.
It seems unlikely that someone would come open the gate and then stand around until the ducks made their way out then shut the gate and leave.
At that time of night I could open my gate and it would take hours if at all that they would get up and find the open gate and leave.
The only scenario involving a human I could see was someone going in the yard and catching them and leaving with them.
If I was to jump to conclusions I would say something like foxes hopped your fence grabbed them and left. Foxes hardly ever leave clues behind and one or two of them will snag a bird take it a safe distance then repeat several times.