In one of my bathrooms on the top floor, I can loudly hear noises that sound somewhat like a bird. The sounds have been going for about a month now. What's going on? Should I be concerned?
You should always be concerned about a new noise in your house. Examine the outside upper story soffit framing to see if any soffits are missing or broken. If so, there's a good chance something's crawled/flown up there. Get a good flashlight and check out the attic by slowly opening the access door/panel and looking around. If you find something up there, well that's another question.
Do woodpeckers live in your vicinity ?
That rattling sound with a few slower bangs after it really sounds like a woodpecker hammering.
The other noises are certainly birds.
That isn't necessarily inside your attic. You be surprised how sound can carry through a structure if it is being knocked on from the outside. And an attic in particular can act like a sound-box amplifying sounds in a strange way.
I would take a flash-light and get into the attic space.
Wait until it starts again (might take a while) while keeping still. You might see movement from bird activity or get a better feel from where the sounds are really come from.