Wow, I took myself off BYC "cold turkey" several months ago because I was spending too much time on it, but I just can't resist this thread.
I hate to use the phrase "self-evident" in anything less important than the U.S. constitution, but this might be one of those times. How can anyone argue that it is impossible to select for a less aggressive rooster when it is clearly done by almost every private breeder with young children? Are there numerous ways to do it? Of course there are, and many have been brought up here. Do some ways get you there slower and some ways get you there faster? Of course different methods have different success rates and speeds, but that doesn't mean that there's only one path towards the goal. Anyone who looks into different lines of almost any dual purpose breed before buying will find that there are huge differences not just in physical characteristics, but also in behavioral characteristics from suppliers that don't use any selection parameters other than egg production (i.e., most hatcheries) verses suppliers that use heavy selection parameters (i,e., most top breeders). If one of those selection parameters is the behavioral traits controlled by brain neurotransmitters, stress hormones, and reproductive hormones (i.e., the genetically-controlled physiological reasons that someone is an aggressive jerk instead of a polite, well-socialized member of your species' social system), then it is clearly possible to select for a sweet rooster. But remember what "select for" means. It doesn't mean that every rooster ever hatched by you will be perfect. It doesn't mean that you don't need to continue the selection process once you've achieved your goal. It's just like any other characteristic that breeders consider in the selection process. Top breeders know that less than 10% of their chicks will grow up to be breeding quality, and if they've worked with a flock for enough time and de-selected undesirable traits well, then hopefully the other 90+% will still represent the breed properly. If a top breeder's flock were to be sold to a high volume hatchery that does no selection, even those excellent birds will devolve into junk (from an SOP viewpoint only, not trying to berate anyone's beloved birds here) over several generations. So the argument that it's not worth doing because it is a never-ending task is ridiculous -- selection for ANY trait is an endless task that can never be ignored, because of course genetic entropy will take over. That's what unselected reproduction does -- for better or worse!
A great example is the RIR. As many on this thread have mentioned, the RIR rooster that most people know is a vicious thing. But they're not supposed to be. A true heritage RIR rooster is a perfectly-behaved farm animal -- he watches out for predators while his girls graze, he protects them from any threats, and he has enough judgment to know that his human guardian is not one of those threats. Unfortunately, there are very few true heritage RIRs left in the U.S. Because of their popularity they have been bred without regard to anything except fertility, and the result is the Production Red, sometimes honestly sold as a Production Red, but frequently sold as a RIR. How exactly are Production Reds (fake RIRs) bred? Picture a giant breeding shed packed tight with 600 hens and 100 roosters. The roosters spend half their day fighting. The winners get to spend the other half of their day breeding. Since a leaner, flighty, high-strung rooster is often better equipped for fighting, this genetic lottery is rarely won by the bird that represents the breed well, as a true RIR is supposed to be a calm, well-muscled, heavy bird that produces an excellent Sunday dinner, but isn't necessarily agile enough to outmaneuver the scrawny violent creature that we've all come to know and dread.
OK, enough of my soapbox!! Breeding a properly behaved rooster is near and dear to me, as I am in the process of breeding a new flock sire. I did not start out planning to breed Red Dorkings. I actually had never heard of the breed. But when my chick order at Sandhill could not be filled as requested in 2012, I was sent 13 Red Dorkings as a substitute for one of my chosen breeds. And I became enthralled with them. They are everything I ever wanted in a chicken. Temptation gave way to new infrastructure and now I'm heading down the road towards becoming a serious breeder. I selected the best two roosters and kept all seven hens. I later culled down to one rooster (not recommended, but had to be done in this case). This year I finally did some test breedings with the 5 best hens to see what traits were hiding in the genetics of this line. Somewhat surprisingly, there were few surprises in the F1s, although I know it's the F2s that can be the most telling. But the behavior aspects of the F1 cockerels is quite straightforward. Using the same rooster over all five hens, the aggressive tendencies of the cockerels (now around 6 months old and full of teenage testosterone) highly corresponds to the "flightiness" of the genetic mother. The more high-strung the hen, the more aggressive the cockerel. The calmer the hen, the less aggressive the cockerel. This has been quite consistent of the 18 cockerels I hatched out. (Admittedly, 18 is not a statistically significant number for research purposes, so I'm not stating this as a factual cause and effect. Just an observation that is consistent over more than just a few birds.) An additional observation is the anxiety level of the cockerels, and their ability to handle stressful situations. That seems to be more related to their early experiences. I brooded them under hens. Two of the hens were excellent mothers, and one was not. The one that was not a good mother kept them warm and protected, but she was anxious herself and a fairly harsh disciplinarian compared to the other two broodies. The three cockerels raised by the poor mother are anxious and have poorer coping skills than all the others, although are not more aggressive (these three chicks had a very calm genetic mother). So from my relatively small but diverse group of Red Dorking cockerels, it seems that aggression is more genetic, and anxiety is somewhat more environmental. Or if you prefer, aggression is more in your genetic nature, and anxiety is more due to your early nurture. How that plays out in behavior depends of what combinations contribute to the final result -- an anxious aggressive bird is the worst of both worlds, and a relaxed, non-aggressive bird is a kid's best friend, but other combinations may be the best bird for your situation, depending on your specific needs.
So, I'm hoping that one of these cockerels will grow into a great rooster. I love Goliath, my current rooster. He has his shortcomings, but his quality is good enough for me to use him as foundation stock towards the SOP. But despite being a totally tame rooster, he has always been a little too territorial, and it's getting worse with age. I didn't know it when I got them, but the Sandhill line of Red Dorkings is known to have aggressive roosters -- well, relatively aggressive, in a breed that is famous for having very sweet and gentle boys. The flock free ranges, and he is very protective of his flock. But he has taken to stalking me constantly. Whenever I'm outside I see him out of the corner of my eye, sneaking around behind bushes, waiting for the moment my head is turned so he can rush up and flog me. He regularly bites me when I'm carrying him around, and will strike out hard with his beak if I walk near his roost. Now admittedly, none of these are abnormal behaviors for a rooster trying to protect his hens. But I want something more. I don't want a bird with no judgment, who acts on just blind instinct to protect. I want a bird who can differentiate between a real threat and their main caretaker. And don't tell me that their brain is too small. I don't believe it. These are the smartest birds I've ever seen, which is why I expect more from the flock leader. So the selection begins ...