Background research is vital for developing a foundational understanding of your topic. It will also help you narrow and focus your research question, choose relevant keywords and search terms, and shape research direction.
In addition to general searching using your favorite search engine or Wikipedia, you may also review newspaper or magazine articles, and longform journalism. Biology encyclopedias can also be useful places to look for information because they are written by experts in the field and will also include references that will direct you to further reading on a given topic.
These selected works and websites will help you to quickly find a definition, explanation of a process, or a brief introduction to a concept.
Grzimek's is a comprehensive reference work on the animal world. The volumes are organized by taxonomy, with information for each organism organized under general topic areas such as reproduction, behavior, ecology, etc.