This has been bugging me for weeks now! I hope someone can help me. There was an animated film that I used to watch when I was a little kid (probably in the early 90's) It's starts with a fuel truck running over a piece of glass in the road and crashing into a tree and all the toxic gas fills the woods and starts killing the animals. One of the animals gets really sick from it (I think her name is Amelia) and her friends have to travel far away to find the plants nessesary to make her better. Along the way they run into like a chior of birds that sing and they have to make a plane out of really big leaves and sticks and stuff to get to the top of a cliff where one of the plants they need is located. Does anyone know what the hell I'm talking about?

Once Upon a Forest (1993) (http://www.imdb.com/title/tt0107745/)