The tuco toucan, the largest member of the tucan family, possesses the largest beak relative to body size of all birds. this exaggerated feature has received various interpretations such as being

This exaggerated feature has received various interpretations such as being adapted for better feeding and temperature maintenance.

Explanation:

The largest beak of Tuco toucan relative to body size is an adaptation for feeding. Tuco toucon use their beaks to pluck fruits to eat, they catch insects, frogs and reptiles for feeding. When sleeping they keep their beaks under their feather to keep itself warm. Also, the large beaks help it radiate heat and maintain its temperature. They increase their blood flow to their beaks and maintain temperature  to survive in the tropical climate.