An introduction to animal behavior: evolutionary theory provides the foundation for the study of animal behavior, charles darwin realized that evolutionary change would occur if natural selection took place. This process happens when individuals differ in their ability to reproduce successfully, as a result of their inherited attributes. Questions about ultimate causes are those that focus on the possible adaptive value of a behavior as well as those that ask how an ancestral trait became modified over time, leading to a modern characteristic of interest. The integrative study of behavior: different populations of birds often sing distinct forms of the same song, called dialects. To understand how birds learn different dialects, we must explore both proximate and ultimate hypotheses for avian song learning: there appears to be little evidence of hereditary differences underlying dialects in several bird species. Instead, young birds appear to learn their distinct songs during a critical window during development.