I was inspired by a recent visit to the Gold museum in Bogota, a truly amazing collection of artifacts from history. Paticularly intriguing were the bird-men displayed. Most of them had these round noses.
According to numerous American cosmologies, the universe was made up of three worlds. Mankind lived in the intermediate world, whereas gods, ancestors and other supernatural beings resided in the upper world or the underworld.
The upper world and the underworld were conceived as having opposing and complementary characteristics, such as light/dark, male/female or dry/wet. The middle world, where people lived combined elements from the other two.
Birds symbolized the upper world.
The bird-men in these ornaments have twisted nose rings with circular tips instead of a beak: they are elements in the transformation into a bird which allude to the ecstatic flight of the shaman.
In my mind, these nose rings bear uncanny resemblence to clown noses.