Why does a California condor have a bald head?

All vulture and vulture-like species have bald heads. The main reason is for sanitation. Vultures eat dead things - often very dead, very putrid, very bacteria-infested things.

If you had to stick your head inside the bloated side of a dead deer for every meal, you'd shave your head too.

It keeps them from having to try and clean the feathers regularly, and keeps bacteria and other lovely gross stuff from growing in the feathers.