The rust on the birdfeeder makes this interesting pattern.

It’s because dissimilar metals have different

electrical potentials, and affinity for electrons, so current flows.

The stainless-steel hanger is passive,

but causes corrosion where it touches the steel structure.

The aluminum rivets also are the source of the corrosion.

Rust spreads out in a circle of equal potential,

so the interesting patterns develop,

and leave a flake of paint that looks like Australia.