Very poor looking blackbird

As the title suggests I have a blackbird that frequents the garden that is in a very sorry state. As the photo shows, is has lost basically all its tail feathers and, presumably as a result of the lack of feathers, his legs are heavily cover in what looks to be excrement. He’s also got very thin, soiled feathers on his breast. I know blackbirds often look pretty scruffy this time of year but this is the worst state I’ve ever seen one in.

He’s still able to fly as he’s able to get up to my window bird feeder, but I’d still like to know if there’s anything that can be done/I can do for this poor boy, or do I just have to hope his feathers grow back?