"ハト"
English title: Pigeon
Uploaded December 19, 2007, with 692,000+ views
Produced by Hadano-P
This song, Hadano-P's fourth and most popular work, is about a pigeon traveling to distant lands. It has entered the Hall of Fame and is featured on the album 初音 ミクベスト ~Impacts~. This song was performed at the 39's Giving Day 2010 concert.
(Taken from Vocaloid Wiki)
If you want to listen to it, here's the download link.