I've read that guineas can be aggressive when adding birds to their flock. Also, I read that the best thing to do is add young guineas to an already established flock of ducks or birds. So what I have done is this. I got my guineas at 6 weeks old and kept them in an extra large wire dog crate on top of my waist high duck coop. They spent 4 weeks in the crate so that both types of birds could get used to each other. Three weeks ago I opened the crate door. The guineas took a few days but they now travel my yard eating bugs and head back to the duck pen and their cage for their treats at night. Also, the only water source around is in the duck pen and in their cage so they come back for water. At night we let the ducks out into the yard to graze while we are doing gardening, yard work, etc... I have noticed that the guineas are always in the middle of my duck flock. If something scares them they will fly and perch on top of the pen fencing. Then after a couple minutes they panic again and fly back to the duck flock. If the guineas are out wandering and we let the ducks out they will sprint like little road runners to be in the middle of the ducks. The ducks just continue looking for bugs and eating, both birds will simply reach right underneath each other or around each other for a choice morsel. My guineas are 13 weeks old now. At what age should I worry about aggression? Or should it be a non-issue since the flocks both get along so well?