An unlearned behavior directly linked to a stimulus that is carried to completion once initiated and is essentially unchangeable is

The answer is: a fixed action pattern.

A fixed action pattern is unlearned, instinctive behavior that is invariant within the species. It is linked to a stimulus that is carried to completion once initiated and is essentially unchangeable. The example for this behavior is Graylag Goose. If an egg is displaced from the nest, the goose will roll it back to the nest. If the egg is removed during the egg-rolling, the goose will continue to roll "imaginary" egg.

A: rachel carson :