Leaving dragons a little aside, a memory came to my mind when I researched about mythological/folk creatures that fly and remembered a very peculiar one: the Firebird. It's basically a glowing bird and it fascinated me! I want a bird like that for my world, a bird that many characters can have as a pet. But I don't want the creature to be magical and as realistic as possible. Is it possible for a bird to glow?
Basically, what I have in mind is: the bird is carnivorous, it feeds on insects. It has feathers in shades of yellow, red and orange. The bird is able to emit light rays through its feathers. The bird is diurnal, but the mating ritual is at night, the ritual is to fly through the night sky and sparkle. The bird chooses when it will emit light. The bird is monogamous, so the feathers will gradually be replaced by normal feathers after the bird finds its partner(well, in some species it's like that, in others the feathers are permanent as some insects are attracted to light, so it's a good hunting tactic). Bioluminescence is autogenic, that is, the bird itself produces it and not a bacterium it eats.
Note: I used google to translate so maybe "shimmering" is wrong. In Portuguese, "cintilante" means something that emits light in short intervals of time. In other words, my bird can glow and go out whenever it wants to create a light show, it doesn't just glow, it fluctuates between glowing and going out.