Why did my Conure die...? D:

by Sydney
(Woodbridge, VA. USA)

Hi.
A few days ago, my beloved Conure died suddenly. The day before he died he was PERFECTLY fine; acting just like himself. But, the next morning he was slowing down and sleeping a lot. That night, he used the last amount of his strength to fly over to me, tweet my name, then he slowly pasted in my arms. I just don't understand why he died and it would put me at peace to know and hopefully prevent his brother from dying from the same reason.
Additional information?
My bird has been on the same food since we got him, he played with his brother every day, we clean his cage constantly, he got lots of sunlight and fresh water. My mom's a bit of a bird freak so his life was pretty good.

Please do give me an answer... My conure Lotus was the best bird I ever had. I still can't believe he's gone. His grave is marked with a Japanese marble tablet and behind that is a porslin Lotus flower.