The secret of the magic mine in waterbirds

Anne Trafton

Almost 150 years ago Charles Darwin revealed a slender bird's beak due to its adaptation to its environment. Now, the Massachusetts Institute of Technology (MIT) team of mathematicians and engineers has given an accurate explanation of how some waterbirds use long, thin beaks to resist gravity and swallow. food into the mouth.

According to an article published in the May 16 issue of the Journal of Natural Science, the team of researchers said the waterbird that resides in the north-west of the US takes advantage of the surface interaction between the inner surface of the mine and the water droplets. to push small pieces of food to your mouth through a long beak.

Surface interactions depend on chemical properties related to liquids, so waterbirds and about 20 species of birds use the same mechanism to be extremely sensitive to any of these impurities. water surface, especially detergent or grease.

'There are a few birds relying on this mechanism to swallow food so they are very vulnerable to oil spills', said John Bush, associate professor of applied mathematics, co-author of the study. know.

For a long time, many wildlife researchers have recorded unusual behavior in waterbirds, spinning on the water, creating whirlpools, pushing crustaceans. on the top surface layer, like tea leaves in a rotating cup.

With a long, narrow beak, waterbirds use a surgical mechanism on the water to push food from the tip of the beak to the mouth.(Photo: Rainey Schuler)

By operating on the surface of the water, they will catch the prey in small droplets (millimeter size). Because the bird beak is pointing downwards during the process of swallowing food, gravity must be defeated, enabling water droplets to move through the long beak, from the tip of the mine to the mouth. Until now, scientists still do not understand the mechanism of this implementation.

Scientists consider that the water bird's strategy of swallowing food is based on the surface tension of water droplets. Surface tension dominates all common liquids, from small rain drops to insects in insects and insects, but the benefits of water for waterbirds are not easily recognized. Key recognition lies in the ability of water droplets to move when birds open and close their beaks like a moving tweezers.

To solve this mystery, Bush worked with Manu Prakash, a doctoral student at the Center for Small Atomic and Atomic Research; At the same time, there was the participation of Professor David Quere (from Paris Polytechnic University) during the time he taught at the Faculty of Mathematics (MIT). They built a model of a beakhole mechanism that allowed the slow motion processes to be studied.

Waterbirds take advantage of surface interaction through a moving contact angle phenomenon to push water droplets containing prey to the throat.(Photo: Robert Lewis)

This process model is based on surface interaction known as contact angle hysteresis (moving contact angle), ignoring the typical obstacle of moving solid objects. For example, raindrops cling to window panes due to contact angle hysteresis. During the time when the bird's beak swallowed food, the two edges of the beaks when opened form a geometrical angle, combined with the contact's latency due to changing the width of the two beaks, will help push the droplets up stairs.

Because the bird's beak as a scissors extends and clamps, every move like that will push the drop of water one step closer to the bird's mouth. It is clear that when the beak is closed, the tip of the droplet moves towards the mouth while the tail of the water droplet pushes (moves) upward, closer to the mouth.

Like the steps on the catwalk, water drops move along the mine at a rate of about 1 meter per second.

This process is called 'capillary ratchet' by the authors , the effect depends on the shape of the bird's beak: long and thin are the most appropriate factors for the method of swallowing food thanks to water . The remarkable point of this study is that the opening and closing mechanism of the angle formed by the two beak edges: 'Changing the angle of a few degrees can make the droplet's movement speed faster or slower. 10 times, ' Quere said.

'Capillary wheels' also depend heavily on the wet state of the beak - the tendency for water droplets to form or the degree of water spread evenly across the bird's surface. Oil and grease are considered to be "wetter" than water, so if the beak is soaked with oil from the oil slicks, it will prevent them from exercising their ability to swallow food.

Researchers note potential applications from nature's design models: 'We are currently working on micro-liquid devices that use this mechanism to push water droplets along. The desired direction, allowing control of every step of the movement of micro droplets at the micro level ', Prakash expressed.
The research was funded by the National Natural Science Foundation, the Scientific Research Center (France) and the Center for Small Atomic and Atomic Research (MIT).

Related videos:

The model of the bird-biting feed mechanism through very small droplet transport capacity, helps MIT researchers discover how waterbirds push food up the throat.Videos are recorded at 2000 frames per second & slow down to 30 frames per second.(Video: Manu Prakash, MIT)

The act of swallowing the food of the red-necked waterbird.MIT scientists point out how birds turn water against gravity when moving prey caught in water, through mines up to the throat.(Video: Don DesJardin)