How can I write the purpose of this experiment?

thanks (: every bit counts.

You wanted to determine the affect (effect?) music has on animal, if it irritates or calms them, etc? Best I could think of xD

The purpose of any experiment is to learn something. You have already state your purpose here: to learn “if music affects animal behavior.” Not knowing the structure of your experiment, I suspect that in practice its purpose may have been somewhat narrower, like: to learn if a certain amount of exposure (duration, volume, etc.) to certain kind(s) of music (string quartets, heavy metal, didgeridoo, etc.) affects the range of behaviors that you tested for in certain species of mammals.

If someone asks, “Yes, but what was your purpose in learning that?” I would say they are no longer asking about the purpose of the experiment, but rather about the purpose of the learning - which may have an immediate practical application, or may be out of purely scientific curiosity, or anywhere in between.