I have around 25 mallards and the 3 oldest drakes are around a year old. I noticed today 2 of them are biting and laying on the other one, it doesn't appear they are hurting him. Is this normal behavior or is there something wrong with the drake that is getting the attention? It has been going on all day and if I separate them the minute they get back together they are at it again. They 2 are not bothering any of the other drakes or females.