As already stated, take Biology and Environmental Science (Field Biology). As for what career options there are, NUMEROUS and very diverse options you face. You could work for Department of Natural Resources, where you could survey wildlife populations and establish limits for game animals, maintain national parks, etc.
If you want my honest opinion, learning about animals is great, but it doesn't mean squat until you learn about bacteria/fungi/viruses, and other microbes, with a great emphasis on learning about PLANTS. I know, you may find plants boring, but you cannot learn about the environment without knowing nearly all there is to know about soil, erosion, types of plants and the climate of the areas in which they grow. The best way to learn about this stuff on your own, or with someone who is like-minded in their aspiration to find a career in such a field. Go outside a lot, (here comes a redundancy) plant plants, observe animals in nature, go and look around in nature, but do not disturb its way of order. Just by being out there, whether you know it or not, you will gain as much knowledge as you are willing to absorb.
Another major base knowledge is marine life. Because the majority of ALL life on earth is found in water, and has unique characteristics, many similarities and differences to the terrestrial ecosystem.
If you heed my advice, you will have the tools to confidently make your decision on what you would like to be.
