Beaks Reflect UV Light

close up view of an emperor penguin in the sunlight near water

Biological Strategy

Emperor penguin

AskNature Team

Image: Jörg Vieli / Pixabay / Free non-commercial use

Modify Light/Color

Color in living systems comes from pigments and the interaction of light with surfaces. Color serves many purposes for living systems, such as attracting prey or mates, providing warnings, or protecting through camouflage. To create the effects needed for each purpose, living systems must control the expression or visibility of pigments and the interactions (such as reflectance and refraction) of light. To do so, they have strategies that modify color or light to increase or decrease the color’s position, intensity, opacity, and more. Male hummingbirds, for example, have brightly colored feather patches on their throats; the coloring comes from pigments, structures that refract light, or a combination of the two. When a male hummingbird hovers near a potential mate, it modifies the angle of these feathers to create a bright, colorful display. However, when it needs to mute the colors to reduce conspicuousness, such as to avoid a predator, it modifies the angle again.

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Send Light Signals in the Non-visible Spectrum

Living systems interact with each other and with their environments to gain information, which is sometimes in the electromagnetic spectrum. Wavelengths of the electromagnetic spectrum are also called the non-visible light spectrum because humans cannot detect them with the naked eye. These include ultraviolet (UV) light, infrared (IR) light, radio waves, and other wavelengths, which living systems can use to send signals. Those signals must not only be targeted to other living systems that can detect them, they must be energy- and material-efficient. This creates both challenges and opportunities. For example, some web-weaving spiders add UV-reflective silk strands to their webs to keep birds and bumblebees (which can see UV light) from crashing into and destroying them. But because the insects the spiders feed on they can’t see UV wavelengths, they fly into the web.

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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 beaks of emperor penguins reflect UV light via a multilayer reflector photonic microstructure.

Image: Birgitta Dresp, Pierre Jouventin, and Keith Langley /

Transmission electron micrograph of the upper region of the beak horn, showing it to be packed with microstructures constituted of multilayer folded membrane stacks. Scale bar, 1.0 mm. Image taken from Dresp, B; Jouventin, P; Langley, K. 2005. Ultraviolet reflecting photonic microstructures in the King Penguin beak. Biology Letters. 1(3): 310-313. This document is downloadable free online from http://171.66.127.192/content/1/3/310.short

“Although the mouths and flanges of begging passerines have been reported to reflect in the ultraviolet (Hunt et al. 2003), this is the first time that the nature of the UV-reflecting microstructures has been characterized in beak tissue of any bird. The ultrastructure of the photonic microstructures found in the present study differs radically from that of those previously described in either bird feathers or skin. The regular multilayer membrane arrays found in the beak horn microstructures closely approximate to two dimensional crystal lattices, strongly suggesting that UV reflectance here is produced by interference between incident light and that reflected from successive folds in these microstructures (Prum & Torres 2003).” (Dresp 2005:312)

Transmission electron micrograph of the upper region of the beak horn of an emperor penguin, showing it to be packed with microstructures constituted of multilayer folded membrane stacks. Scale bar, 1.0 mm.