Who is the oldest?

The four harmonious friends. A Bhutan story about friendship and respect.

A bird, a rabbit, a monkey and an elephant lived by a fruit tree. They hoped to find out who was the oldest among them.

The elephant said when he was little the tree was already fully grown, the monkey remembered the tree when it was still small. The rabbit said the tree was only a sapling when rabbit was a bunny. The bird shared it had eaten the fruits nearby the tree, and the bird excreted the seeds which eventually grew into the tree.

So who is the oldest?