Beak Size Optimized for Thermal Regulation

tropical bird with large bill sits against a green background

Biological Strategy

Birds

AskNature Team

Image: Geoffrey Baumbach / Unsplash / Free non-commercial use

Optimize Shape/Materials

Resources are limited and the simple act of retaining them requires resources, especially energy. Living systems must constantly balance the value of resources obtained with the costs of resources expended; failure to do so can result in death or prevent reproduction. Living systems therefore optimize, rather than maximize, resource use. Optimizing shape ultimately optimizes materials and energy. An example of such optimization can be seen in the dolphin’s body shape. It’s streamlined to reduce drag in the water due to an optimal ratio of length to diameter, as well as features on its surface that lie flat, reducing turbulence.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Birds

Class Aves (“bird”): Eagles, hawks, sparrows, parrots

Birds are evolutionary engineering marvels. They are descended from dinosaurs, but are far from our idea of heavy, scaly reptiles. Of the specific adaptions that set them apart, most notable is flight—although some mammals can fly, birds take the prize for abundance in the skies. Many birds have hollow, lightweight skeletons and specially-designed wings to help them stay aloft. They also have feathers made of keratin that help them stay warm, attract mates, and improve navigation and aerodynamics in flight. In contrast to their dinosaur ancestors, they lack true teeth and have replaced them with specialized beaks and bills.

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The beak size of birds is optimized for thermal regulation because they vary in size relative to latitude and environmental temperature, a concept called Allen's rule.

“By examining bill sizes of a diverse range of bird species around the world, researchers have found that birds with larger bills tend to be found in hot environments, whilst birds in colder environments have evolved smaller bills.

“The study…provides evidence that maintaining body temperature in a bird’s natural environment may have shaped the evolution of bird bills…

“The research validates a 133-year-old ecological theory called Allen’s rule, which predicts that animal appendages like limbs, ears, and tails are smaller in cold climates in order to minimize heat loss.” (The University of Melbourne 2010)