Which is an example of an adaptation?

An adaptation is a characteristic that has evolved over time to help an organism survive and reproduce in its specific environment. Bird migration serves as a prime example of adaptation because it illustrates how certain bird species change their location seasonally to find food, escape harsh weather, or reproduce effectively. This behavior is a direct response to environmental conditions and ensures that birds can access the resources they need at different times of the year.

In contrast, cloud formation, soil erosion, and river currents are natural phenomena or processes that do not involve changes made by organisms to enhance their survival. While these processes may influence ecosystems and the organisms within them, they are not adaptations that arise from biological evolution or behavioral changes aimed at improving the chances of a species' survival in its environment.