In yesterday's heat I witnessed the following - both juveniles were chasing parent for food then, close to the ground, one attacked the other, who then laid on its back on the mulch in surrender. The attacker moved away, the other bird stood and was attacked again. It lay on its back for a good minute and I was becoming concerned. As I stood up, it righted itself (to my relief) and I was able to get this photo.
and here's the assailant - you can tell it's hot by the open beak and wings held away from body
Parent bird very hot too, as it looks on -