The avian bill is a textbook example of how evolution shapes morphology in response to changing environments. Bills of seed-specialist finches in particular have been the focus of intense study demonstrating how climatic fluctuations acting on food availability drive bill size and shape. The avian bill also plays an important but under-appreciated role in body temperature regulation, and therefore in energetics.

Click on the link to read the rest of the article: The evolution of the avian bill as a thermoregulatory organ – Tattersall – 2016 – Biological Reviews – Wiley Online Library