The problem there isn't your receptors, which are UV sensitive. The problem is your lens, which filters it out. Remove the lens and you can see UV just fine.

Until you get eyeball cancer, that is. UV is mutagenic. That's why you filter it out.

People with cataracts get replacement lenses, and some exist that don't filter the UV. I think they're hard to get, what with the whole "eyeball cancer" thing. But if I get to my 70s and need replacement lenses (I do have a family history), I'm going to campaign to see if I can spend a couple of decades looking at the pretty birdies.