What if your bird is fluffing his feathers a lot and spending a lot of time at the bottom of the cage?

This means either your bird is extremely sick or something is really bothering it, like its surroundings or something.

You should firstly take him to the vet right away if this has been going on for a long time.

If it was very recent, check the cage surroundings for things that could be bothersome, such as an air humidifier, dehumidifier, heater, air conditioner, etc