What can dried blood tell an expert?

Making a dry blood test can diagnose hepatitis C

Dry blood samples can detect both antibodies and hepatitis virus RNA successfully. It involves obtaining a few drops of blood by fingerprinting, and letting them dry on a specially specific absorbent paper card.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.