Answer:
C. The two birds have different ecological niches that allow coexistence.
Step-by-step explanation:
An ecological niche is a term for the position of a species within an ecosystem. This include how it meets its needs for food and shelter, survives, and reproduces.
It can also be explained as all the interactions of a specie with the biotic and abiotic factors of its environment.
It should be understood that, when a specie possess an ecological niche in an ecosystem, it most likely reduces the amount of competition for resources that species will encounter.
In this case, the reason why two species of cliff-dwelling birds can coexist is that they have different ecological niches that allow coexistence.