Beak Snaps Shut

photograph of a blue and green bird in front of green background

Biological Strategy

Hummingbirds

AskNature Team

Image: Philip Brown / Unsplash / Free non-commercial use

Store Energy

Once a living system captures energy or transforms one energy form into another, it must frequently save that energy for future use. But energy is difficult to store in some forms. So living systems need strategies to either use energy quickly, or to convert it from forms that are difficult to store (such as electrical or kinetic) to more storable forms. For example, grasshoppers store energy as potential energy in an elastic material in their tendons. When they need to jump, that energy converts into kinetic energy, providing the force needed to escape predators.

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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 of the hummingbird can snap closed to capture insects due to stored elastic energy.

“The hummingbird beak, specialized for feeding on floral nectars, is also uniquely adapted to eating flying insects. During insect capture the beak often appears to close at a rate that cannot be explained by direct muscular action alone. Here we show that the lower jaw of hummingbirds has a shape and compliance that allows for a controlled elastic snap. Furthermore, hummingbirds have the musculature needed to independently bend and twist the sides of the lower jaw. According to both our simple physical model and our elastic instability calculation, the jaw can be smoothly opened and then snapped closed through an appropriate sequence of bending and twisting actions by the muscles of the lower jaw.” (Smith et al. 2011:41)

Part of the trick lies in how the hummingbird’s beak is built. While other insect-eating birds such as swifts and nighthawks have a cartilaginous hinge near the base of their beaks, hummingbird beaks are solid bone. They’re also incredibly thin, so that the lower beaks are stiff yet springy. The researchers’ mathematical model revealed that the downward bend of the hummingbird’s lower beak puts stress on the bone, storing elastic energy which eventually powers its sudden snap closure. (From Smith 2011, EurekaAlert)

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