The food chain is a natural process that is important for every level to be balanced.
Here the caterpillar eats the plants, a bird eats the caterpillar then the small bird can be eaten by a large bird.
If in case the caterpillar dies and there is no caterpillar to eat the plants, birds won't eat the plants and hence the growth of the plants will be uncontrollable.
This is a system created by nature to keep all the levels balance and none would perish without others.