Scientists have left a story incomplete about the evolution of beak size. In the 1990s, researcher Russ Greenberg from the Smithsonian Institution in the United States began to discover a new question. This question was concerning to the link between environment and the evolution of beak size. This question was stimulated by Allen's Rule, which states that warm-blooded animals living in cold climates will have shorter limbs and appendages than those that live in warmer climates.

The scientists stated that the biological mechanism behind this rule is thermoregulation -- more body surface area helps animals to shed heat better. On the other hands, less surface area helps the animals to conserve the heat. As far as the bird’s beak is concerned, it plays a huge role in thermoregulation. Thermoregulation has many blood vessels and is not covered in feathers.

Then the question arises whether hotter climates cause larger beaks and colder climates beget smaller ones. Certainly, studies exposed that climate has influenced beak size. However, it is unclear which type of climate had more of an overall impact.

By: Priyanka Negi

Content: www.sciencedaily.com