Rock here is a ptarmigan. He's Herb's best friend and roommate. The design is still rough. Up until now, he looked much more like a rooster, which isn't gonna work. NOW, he looks more like a ptarmigan, yet less like the other characters. So the design is still in progress..
The ptarmigan is the state bird of Alaska. In the winter their feathers go white and the ridges on the males' foreheads pop up all bright red. This is in the interest of simultaneously hiding from predators and attracting the attention of mates. A highly nuanced maneuver to be sure.