The process by which a species becomes better suited to its environment through natural selection is called adaptation.

Here's a breakdown:

* Natural Selection: This is the mechanism by which individuals with traits that make them better suited to their environment are more likely to survive and reproduce.

* Adaptation: This refers to the changes in a species over time that result from natural selection. These changes can be physical (like a beak shape) or behavioral (like migration patterns) and they help the species survive and reproduce in its environment.

In short, natural selection is the process, and adaptation is the result.