matters - if the males have their red shoulders painted black they keep their territory, but if they can't sing, they lose it. The cool thing is that you can temporarily mute them by popping the vocal sac, and in a couple of weeks it heals. The male loses his territory for those two weeks, then returns full throttle and drives off the new male once his singing ability is restored. Females only care about real estate and don't relocate during this process."
Finally, for your viewing AND listening pleasure, following is a short video of the stud above countersinging with several neighboring birds.