Try specific terms first,
then try more general ones.
- Specific terms (Northern Flicker or Colaptes auratus) give fewer but more precise results
- General terms (birds or woodpeckers) give more but less precise results
Searching specific terms may miss a book about the broader topic with just a chapter on your topic.
Use both scientific and common names for organisms, connected with or, as above.
Try using truncation (forest* will find forest, forests and forestry) and variant spellings so you won't miss important titles.