Large, mountain-mounted, alpenhorn from the 1959 Dr. Seuss children's book Happy Birthday to You! A traditional part of the culture of Katroo, it is blown at dawn on someone's birthday by the Birthday Horn-Honker. It depends on how densely or sparsely populated Katroo is, but that's probably every morning.
There is only one Birthday Horn, and it resides on top of Mt. Zorn.