Plumage Traps and Releases Air for Aquatic Launch

emperor penguin launching out of the water

Biological Strategy

Emperor penguin

AskNature Team & Cuentero Productions

Image: Christopher Michel / Flickr / CC BY - Creative Commons Attribution alone

Move in/on Liquids

Water is not only the most abundant liquid on earth, but it’s vital to life–so it’s no surprise that the majority of life has evolved to thrive on and under its surface. Moving efficiently in and on this dense and dynamic substance presents unique challenges and opportunities for living systems. As a result, they have evolved countless solutions to optimize drag, utilize surface tension, fine tune buoyancy, and take advantage of various types of currents and fluid dynamics. For example, sharks can slide through water by reducing drag due to their streamlined shape and specially shaped features on their skin.

Search this Function

Modify Speed

Modifying speed or magnitude of velocity is important for some living systems because it enables them to control their movement to access resources, escape predators, and more. Modifying speed requires not only overcoming inertia, but also minimizing the energy needed to make the change. Therefore, living systems have strategies to safely shift from fast to slow or slow to fast. An example is a bird called the kingfisher, which streamlines its body and feathers to quickly move from hovering over water to diving through the air and into the water. Once in the water, the kingfisher slows down by spreading its wings to avoid diving too deep.

Search this Function

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.

Search this Living System

Micro-bubbles released from the Emperor penguin’s feathers act as a natural turbo boost, creating a lubrication layer around its body that reduces drag and enhances the bird's aquatic speed, propelling it from water to ice with graceful efficiency.

Introduction

In the stark, frozen territories of Antarctica, the Emperor penguin stands as the tallest and heaviest of all penguin species, clothed in a striking tuxedo of black and white plumage. Beyond its distinctive appearance, this penguin exhibits a remarkable for exiting the icy waters—a balletic leap, powered by micro-bubbles released from its feathers. These bubbles create a lubrication layer, significantly reducing drag and enabling explosive leaps onto ice ledges above the sea surface.

The Strategy

The Emperor penguin has mastered what might be termed a biological technology akin to a torpedo launch system. After grooming its dense feathers to trap air, the penguin dives deep, sometimes up to 20 meters below the surface. Here, the real mechanics come into play: as it ascends, it systematically compresses its feathers to release the trapped air as micro-bubbles. This action forms a sleek, lubricating coat around its body, drastically reducing water resistance. The continuous cloak of bubbles works like a natural propulsion system, allowing the penguin to break the water’s surface with enough momentum to vault onto the ice—mirroring the rapid, streamlined firing of a torpedo.

The Potential

The Emperor penguin’s air-trapping feather structure offers a blueprint for cutting-edge designs in both marine engineering and competitive swimwear. By replicating the feather’s ability to trap and strategically release air, engineers could develop marine vessels with external surfaces designed to reduce hydrodynamic drag in a similar manner. For swimmers, incorporating micro-fabric technologies that the penguin’s plumage could minimize resistance, enhancing speed and efficiency in the water: how about those hydrodynamics! These innovations could lead to more energy-efficient transportation and performance-enhancing sports apparel, demonstrating how biomimetic principles can merge sustainability with advanced technological design.

Before exiting the water, the penguin swims at the surface, where it is believed that it loads its dense coat of feathers with air via grooming. The bird then dives to a depth of 15 to 20 meters. During this dive or at the bottom, it depresses its feathers, thereby creating less space for the air to be stored and releasing micro-bubbles. Throughout its ascension, the penguin releases these bubbles in a controlled way, creating a layer of micro-bubbles over most of its body surface. This lubrication layer reduces drag, enabling the penguin to swim faster and to overcome gravity so that it can successfully launch from the water.

This summary was contributed by Ashley Meyers

Check out this National Geographic video to see the penguin's strategy in action.

Last Updated June 12, 2024

References

“To jump out of water onto sea ice, emperor penguins must achieve sufficient underwater speed to overcome the influence of gravity when they leave the water. The relevant combination of density and kinematic viscosity of air is much lower than for water… Analysis of published and unpublished underwater film leads us to present a hypothesis that free-ranging emperor penguins employ air lubrication in achieving high, probably maximal, underwater speeds (mean ± SD: 5.3 ± 1.01 m s–1), prior to jumps. Here we show evidence that penguins dive to 15 to 20 m with air in their plumage and that this compressed air is released as the birds subsequently ascend whilst maintaining depressed feathers. Fine bubbles emerge continuously from the entire plumage, forming a smooth layer over the body and generating bubbly wakes behind the penguins… From simple physical models and calculations presented, we hypothesize that a significant proportion of the enhanced ascent speed is due to air lubrication reducing frictional and form drag, that buoyancy forces alone cannot explain the observed speeds…” (Davenport et al. 2011: 171)

“Before jumping out of the water onto ice, the penguins swim at the surface and then dive on inspiration (Kooyman et al. 1971). We believe they dive with plenty of air in the plumage, with erected feathers making room for an air layer about 25 mm thick (following Du et al. 2007). Kooyman et al. (1971) described the grooming behaviour by which surface swimming emperor penguins load their plumage with air and we confirmed this by observation… They subsequently dive to ~15 to 20 m (by which depth the air volume will have decreased by a substantial amount…). During the dive, or when achieving that depth, they depress the feathers (to fix the plumage volume at the new, decreased level). When the birds swim quickly upwards, the decompressing air will flow out by virtue of the available fixed plumage volume being substantially less than the initial volume. Plumage consists of a fine, multi-layered mesh over the whole of the body surface comparable to a porous medium with an estimated pore size of <20 μm (Du et al. 2007), so the expanding air will automatically issue as small bubbles. This arrangement resembles the flat-plate experiments of Sanders et al. (2006), who used a 40 μm pore size sintered stainless steel strip for microbubble air injection. The ‘active’ part of the process consists solely of maintenance of depressed feathers during the near vertical phase of the ascent in order to regulate expulsion of air driven by decompression. As bubbles continue to enter the boundary layer along the plumage, they are swept downstream and move outwards, thus increasing the void fraction in the boundary layer downstream to finally leave in the wake behind the bird; or they coalesce with other bubbles to form rather large bubbles at the outer edge of the boundary layer…” (Davenport et al. 2011: 175-176)

“…Emperor penguins ascending rapidly in the water column to jump onto ice shelves emit bubble clouds into the turbulent boundary layer over most of the body surface throughout their ascent. Emission does not diminish as a penguin approaches the surface, but increases. Because the bubbles are produced over most of the body surface, their drag-reducing function should exceed the performance of marine engineering plate/ship models described so far, in which maintaining sufficient bubble coverage within the turbulent boundary layer is a major problem.” (Davenport et al. 2011: 180)

Journal article

Drag reduction by air release promotes fast ascent in jumping emperor penguins—a novel hypothesis

Inter-Research | Davenport J; Hughes RN; Shorten M; Larsen PS

embedly preview

AskNature