Featured Research

from universities, journals, and other organizations

Gravity-defying Bird Beak Mystery Solved: Shorebirds Benefit From Surface Tension

Date:
May 17, 2008
Source:
Massachusetts Institute of Technology
Summary:
As Charles Darwin showed nearly 150 years ago, bird beaks are exquisitely adapted to the birds' feeding strategy. A team of mathematicians and engineers has now explained exactly how some shorebirds use their long, thin beaks to defy gravity and transport food into their mouths. Some species rely exclusively on a feeding mechanism that takes advantage of water's surface tension, and so are extremely vulnerable to oil spills.

MIT researchers have figured out how the phalarope, a shorebird with a long, narrow beak, transports its food from the tip of its beak to its mouth. Here the bird feeds by pecking at the water surface.
Credit: Photo / Rainey Schuler

As Charles Darwin showed nearly 150 years ago, bird beaks are exquisitely adapted to the birds' feeding strategy. A team of MIT mathematicians and engineers has now explained exactly how some shorebirds use their long, thin beaks to defy gravity and transport food into their mouths.

Related Articles


The phalarope, commonly found in western North America, takes advantage of surface interactions between its beak and water droplets to propel bits of food from the tip of its long beak to its mouth, the research team reports in the May 16 issue of Science.

These surface interactions depend on the chemical properties of the liquid involved, so phalaropes and about 20 other birds species that use this mechanism are extremely sensitive to anything that contaminates the water surface, especially detergents or oil.

"Some species rely exclusively on this feeding mechanism, and so are extremely vulnerable to oil spills," said John Bush, MIT associate professor of applied mathematics and senior author of the paper.

Wildlife biologists have long noted the unusual feeding behavior of phalaropes, which spin in circles on the water, creating a vortex that sweeps small crustaceans up to the surface, just like tea leaves in a swirling tea cup.

The birds peck at the surface, picking up millimetric droplets of water with their prey trapped inside. Since the birds point their beaks downward during the feeding process, gravity must be overcome to get those droplets from the tip of the bird's long beak to its mouth. Until now, scientists have been puzzled as to how that happens.

Scientists speculated that the feeding strategy depended on the drop's surface tension. Surface tension normally dominates fluid systems that are small relative to raindrops (for example, the world of insects), but it was not clear how it could benefit shorebirds. A key observation was that in order to propel the drop, the birds open and close their beaks in a tweezering motion.

To unravel the mystery, Bush teamed up with Manu Prakash, a graduate student in MIT's Center for Bits and Atoms, and David Quere, of the Ecole Polytechnique in Paris, a visiting professor in MIT's math department at the time of the study. They built a mechanical model of the phalarope beak that allowed them to study the process in slow motion.

The process depends on a surface interaction known as contact angle hysteresis, typically an impediment to drop motion on solids. For example, raindrops stick to window panes due to contact angle hysteresis. In the case of the bird beak, the time-dependent beak geometry couples with contact angle hysteresis to propel the drop upward.

"This may be the first known example where droplet motion is enabled rather than resisted by contact angle hysteresis," Bush said.

As the beak scissors open and shut, each movement propels the water droplet one step closer to the bird's mouth. Specifically, when the beak closes, the drop's leading edge proceeds toward the mouth, while the trailing edge stays put. When the beak opens, the leading edge stays in place while the trailing edge recedes toward the mouth.

In this stepwise ratcheting fashion, the drop travels along the beak at a speed of about 1 meter per second.

The efficiency of the process, which the authors dub the "capillary ratchet," depends on the beak shape: Long, narrow beaks are best suited to this mode of feeding. The study highlights the sensitivity of this mechanism to the opening and closing angles of the beak: "Varying these angles by a few degrees can change the drop speed by a factor of 10," Quere said.

The capillary ratchet also depends critically on the beak's wettability--a measure of a liquid's tendency to bead up into droplets or spread out to wet its surface. Oil is much more "wetting" than water, so if the beak is soaked in oil from a spill, this process won't work.

The researchers note a potential application of nature's design: "We are currently exploring microfluidic devices in which this mechanism could be exploited for directed droplet transport, allowing for controlled stepwise motion of microliter droplets," Prakash said.

The research was funded by the National Science Foundation, the Centre National de la Recherche Scientifique (France) and MIT's Center for Bits and Atoms.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. Note: Materials may be edited for content and length.


Cite This Page:

Massachusetts Institute of Technology. "Gravity-defying Bird Beak Mystery Solved: Shorebirds Benefit From Surface Tension." ScienceDaily. ScienceDaily, 17 May 2008. <www.sciencedaily.com/releases/2008/05/080515145426.htm>.
Massachusetts Institute of Technology. (2008, May 17). Gravity-defying Bird Beak Mystery Solved: Shorebirds Benefit From Surface Tension. ScienceDaily. Retrieved November 24, 2014 from www.sciencedaily.com/releases/2008/05/080515145426.htm
Massachusetts Institute of Technology. "Gravity-defying Bird Beak Mystery Solved: Shorebirds Benefit From Surface Tension." ScienceDaily. www.sciencedaily.com/releases/2008/05/080515145426.htm (accessed November 24, 2014).

Share This


More From ScienceDaily



More Plants & Animals News

Monday, November 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Ebola-Hit Sierra Leone's Late Cocoa Leaves Bitter Taste

Ebola-Hit Sierra Leone's Late Cocoa Leaves Bitter Taste

AFP (Nov. 23, 2014) The arable district of Kenema in Sierra Leone -- at the centre of the Ebola outbreak in May -- has been under quarantine for three months as the cocoa harvest comes in. Duration: 01:32 Video provided by AFP
Powered by NewsLook.com
Anglerfish Rarely Seen In Its Habitat Will Haunt You

Anglerfish Rarely Seen In Its Habitat Will Haunt You

Newsy (Nov. 22, 2014) For the first time Monterey Bay Aquarium recorded a video of the elusive, creepy and rarely seen anglerfish. Video provided by Newsy
Powered by NewsLook.com
Birds Around the World Take Flight

Birds Around the World Take Flight

Reuters - Light News Video Online (Nov. 22, 2014) An imperial eagle equipped with a camera spreads its wings over London. It's just one of the many birds making headlines in this week's "animal roundup". Jillian Kitchener reports. Video provided by Reuters
Powered by NewsLook.com
Could Your Genes Be The Reason You're Single?

Could Your Genes Be The Reason You're Single?

Newsy (Nov. 21, 2014) Researchers in Beijing discovered a gene called 5-HTA1, and carriers are reportedly 20 percent more likely to be single. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins