I'm raising mallards and they about 4 weeks old. I had 6 until last week, when my dog got out and killed 2 of them. The problem is I'm pretty sure all I've got left are 3 drakes and 1 duck. I'd like to get some more to replace the ones I've lost. Is it better to introduce ducks when there younger then waiting until later to add more? I hope to get them ordered in the next couple of days.