SAVE stands for “Smart Attribute Value Elimination.” It is a patented feature of the iBird search engine. SAVE prevents you from selecting search criteria that will yield zero results. It works by hiding options that do not match any species.
For example, one of the option in the shape category is “Hummingbird-like.” If I choose size as “Very Large,” and then I open the shape category I can no longer see the “Hummingbird-like” option. This is because there are no very large birds with the hummingbird shape.