Rapist Roosters

The chicken farmer told me that half of his roosters were rapist-murderers. I was stunned when I heard that. There is no species alive in nature where half males kill reproductive age females. There had to be something seriously wrong with those birds.

(...)

A normal rooster does a little courtship dance before trying to mate with a hen. The dance is hardwired into the rooster's brain; it is instinctual behaviour, or what animal ethologists call a fixed action pattern. All normal roosters do it.

The dance triggers a fixed action pattern in the hen's brain, and she crouches down into a sexually receptive position so the rooster can mount her. She doesn't crouch down unless she sees the dance. That's the way her brain is wired.

But half of roosters had stopped doing the dance, which meant that the hens had stopped crouching down for them. So the roosters had become rapists. They jumped on the hens and tried to mate them by force, and when the hen tried to get away, the rooster would attack her with his spurs or his toes and slash her to death.

Temple Grandin: Animals in Translation