Noise is one of the issues with wildlife sound recording, and manufacturers often present noise specs in different ways, making it harder to work out if there are unnecessary limitations in a particular equipment combination.
This calculator is an attempt to relate the noise and level specs of your microphone and recorder to give you an indication of the maximum and minimum sound levels you can handle. It is necessarily an approximation, based on the assumption that your microphone and recorder noise are reasonably evenly spread across the frequency spectrum. The unweighted recorder noise is scaled down by 5dB to approximate the effect of A weighting. This calculator uses similar principles to this page.
Raw numbers don't tell the whole story about noise, but gives an overall feel of possible issues. Every effort has been made to ensure accuracy, but mistakes are possible - consult the manufacturer's literature to confirm specs - most items are linked to the manufacturer's page.