How to care for an old pigeon?

Can you take it to a veterinarian?

There could be all sorts of things wrong with it...disease, injury, nutritional deficiency...the list goes on.

Pigeons tame easily and make good pets. But if this one is injured or sick it might require medical attention.

We called a local animal protection organization (Tierschutzverein) and they'll send someone to pick it up tomorrow, so all is fine.

Would have loved keeping a bird for once but don't really want to put in the effort so it's better this way.

Since you're only keeping it overnight, just keep it covered.

I've heard pigeons make great pets if you're interested. They're not very expensive (Get a large dog crate to keep them, use pads for diapers or they'll shit on everything you love. That's about it) they're not as noisy or destructive as other birds, they're pretty easy to tame and they're adorable. Would recommend.