Question

Why does the bulbul hide itself in the bushes?

Answer 1

Bulbul was in search of food in field. But it hears the dry leaves crackling sounds there due to which it hide itself in the bushes. This  sound was actually due to a cart wheels running by a driver in the fields.
The bullbul made an imagination that forest is on the fire by seeing the smoke from cart so it wants to rush towards it's nest where it's child was helpless so bubul wants to protect them.

Answer 2

While the bulbul is in the forest, it hears the sound of dry leaves crackling under the wheels of a bullock cart. The bird sees the cart fully loaded and the driver fast asleep. Worried that the whole forest will catch fire if the cart load topples, the bird goes into hiding. It even imagines the forest being set ablaze and wants to rush to its children. But, fear grips the bulbul and the bird is not able to move from the place.