Reuniting two roosters

[cski]

My neighbor wanted to get rid of one of their roosters. We took him and put him in a separate run (the rooster not my neighbor lol) and coop from the rest of the flock. Had him for about a week, then my neighbor wanted to get rid of a second one. We though fine we will take him since the two knew each other and got along before, they can keep each other company in their separate run while they get used to seeing our existing flock. Well when the second rooster was placed in the run with the first rooster, and even though they knew each other and was only separated for about a week, rooster 1, the bigger one attacked rooster 2 to the point of drawing blood. Rooster 1 wanted no part of rooster 2. We have them now separated in two separate runs. We are now thinking of keeping rooster 1 in his own run and maybe getting 3 or 4 hens for him to be in charge of. We would rather just be able to have rooster 1 get along with rooster 2 and the rest of the flock. Would anyone know why rooster 1 would reject rooster 2 even if they got along before?

 

[sourland]

Normal chicken behavior. Once a rooster defines territory/flock as his own he wants no intruders. It's all about the DNA.