If you choose psychology for your major, you will most likely still have the option to take some animal related classes, but the majority of your courses will focus on the human mind. If you know that you want to focus on animal behavior, I would look into Biological Sciences or more specific programs like Animal Behavior and Ethology. There are a lot of other courses of study that look at Animal Behavior as well. Behavioral ecology studies the evolutionary basis for why animals act the way the do. In Environmental Toxicology, we often look at animal behavior to help understand the health of the environment (sentinel species, indicator species, mutant species).
If you want to go into research, which I'm guessing you do by the hashtag, Biological Sciences is a good way to go. I took lots of animal related biology courses and minored in psychology, which gave me the best of both worlds.
Also, keep in mind that you don't have to commit to one course of study right away. It's good to have an idea of what you want to study (and you may even have to declare a major when you apply), but you aren't stuck with that major forever. If you can't decide which direction you want to go, take general education classes your first semester and classes that can be applied to either degree you are deciding between.
Bailey recommends the following next steps:
I do not know of a school that offers an undergraduate program in animal behavior related to psychology, but that does not mean that you cannot pursue this path during undergraduate life. A major in psychology will allow you to learn about behavior. You can seek out hands on experience through research opportunities related to your field of interest. Although your major during undergrad does matter a bit, your hands-on experiences will really make a difference in helping expose you to your future career of choice.