A year passes and there's been no word from Don Pedro, so the king sends Don Diego, the second son, on his way to find the Adarna bird. He wastes no time getting ready and goes off on his horse, aiming to find the Tabor mountains and the bird that lives in it.
He wanders for more than five months in the fields, and when he gets to the upwards path and goes up, his horse dies as well upon reaching the top. Same as with Don Pedro, he takes his provisions and goes to the Tabor mountains on foot.
Upon reaching the mountain, he sees the Piedras Platas, still being a shiny tree as ever. Remembering that the Adarna bird makes its home there, he stays there as well. He also gets a bit too fascinated with the shiny tree, and the crystal-like rock that's below it (I think it might be Don Pedro in rock form...), that it occupies his time until around 5 in the afternoon, when the other birds start showing up.
Just like before, the other birds don't perch on the shiny tree, and this puzzles Don Diego quite a bit. Still, he stays until it gets dark, and unlike Don Pedro before him, he actually gets to see the Adarna bird in all its beauty. He plans to capture it, but its song is so enthralling that it puts him to sleep. And after the bird finishes its singing session, it poops, and that lands on him, turning him into stone as well.
I am now curious as to how Don Juan is going to go about capturing the bird. I know part of what happens, but since I didn't read this back then (I think our school went with Florante at Laura instead), I genuinely don't know. Cause this part (the thing with Don Diego) really gives a better idea of how challenging the task is and also raises the stakes (there's only one more son who could do it, although aren't there other people who could do this???).
Also, my first thoughts regarding the crystal rock thing were "Wouldn't Don Diego be able to see that it looks like a person?" But then, it has been a year, at least, and we don't really know how much weathering and erosion happens in that place. Who knows, right?