There are a variety of techniques that can help you to find sources for your research. They include:
1. Identify new or different keywords to search.
2. Try searching in a different database.
3. If you've already found some sources, look at their bibliographies or list of sources cited to see if anything listed is pertinent to your research.
4. Think more broadly about what is relevant.
For example, if you were researching the impact of deforestation on bird species in the Florida Keys, consider whether sources that discuss the impact of deforestation on birds in other parts of Florida, or the southern United States, or other tropical archipelagos would be relevant.
5. Ask a librarian.
Librarians are trained professionals who can help you find the information you need.