When Hiro was first discovered, there were bushes and trees all around him. After that scene, the area was cleared out almost like a miniature valley for the rest of the movie. See more
Narrator: Suddenly, Spencer whistled long and hard! James and Toby heard Spencer. Suddenly, James and Toby steamed out. Spenser had puffed to close to Hiro! James blew his whistle /whoo whoo!\, and Toby rang his bell /ching ching-ching ching!\. Together they chased the mighty Spencer down the track and away from Hiro.