Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Slow-motion video study shows shrews are highly sophisticated predators

12.02.2008
Strange as it seems, the smallest mammal
Is the shrew, and not the camel.
And that is all I ever knew,
Or wish to know, about the shrew.
--Ogden Nash

Shrews are tiny mammals that have been widely characterized as simple and primitive. This traditional view is challenged by a new study of the hunting methods of an aquatic member of the species, the water shrew. It reveals remarkably sophisticated methods for detecting prey that allow it to catch small fish and aquatic insects as readily in the dark as in daylight.

It is a skill set that the water shrew really needs. About half the size of a mouse, water shrews have such a high metabolism that they must eat more than their weight daily and can starve to death in half a day if they can’t find anything to eat. As a result, water shrews are formidable predators ounce for ounce.

“Water shrews do much of their hunting at night so I began wondering how they can identify their prey in nearly total darkness,” says Ken Catania, the associate professor of biological sciences at Vanderbilt who headed the study.

Catania teamed up with James Hare and Kevin Campbell at the University of Manitoba and used a high-speed infrared video camera to answer this question. The results of their study are reported in a paper titled “Water shrews detect movement, shape, and smell to find prey underwater” published Jan. 9 in the Proceedings of the National Academy of Sciences.

“Our research confirms that shrews in general, and water shrews in particular, are marvels of adaptation, with specializations and behaviors that put many other mammals to shame,” says Catania.

The researchers needed a high-speed camera because of the water shrew’s lightning-fast reflexes: It can launch an attack in under a 50th of a second of detecting the presence of prey and opens its mouth in preparation to take a bite in a 20th of a second. To determine how the shrews hunt in the dark, the scientists also had to monitor their behavior in the infrared portion of the spectrum, which is beyond the shrew’s visual range.

Their observations revealed that the tiny animals can catch prey just as quickly and efficiently at night as they do during the day and determined that they use three basic methods to do so. Working in darkness, water shrews:

Detect water movements caused when prey animals try to swim away;
Identify the shape of prey species using their whiskers;
Use their sense of smell underwater by blowing air bubbles out of their nose and then re-inhaling them.

Catania had discovered the third of these methods – the shrews’ ability to follow scent trails underwater by exhaling air bubbles and then re-inhaling them – in a 2006 study published in the journal Nature. This ability allows diving water shrews to literally sniff out the general location of underwater prey.

In the current paper, the researchers discovered that the water shrews use two additional methods to zero in on toothsome targets. They use their sensitive whiskers to determine the shape of objects that they encounter. And they are acutely sensitive to sudden water currents like those generated when a fish or insect attempts to swim away.

“This combination of methods poses a serious conundrum for prey,” Catania observes. “If they freeze, they risk detection from touch or olfaction. But, if they try to swim away, they generate water currents that can reveal their location.”

After observing the water shrews’ natural hunting behavior in nearly total darkness, the researchers devised a series of experiments to identify the specific detection methods that the tiny hunters use and to rule out some others.

By recording audible and ultrasonic calls, the researchers were able to rule out the possibility that the tiny shrews use sonar, echolocation or electrical sensitivity (electroreception) to find prey.

To test water shrews’ response to water currents, the researchers equipped a small, glass-bottomed aquarium with several small water jets. They put individual water shrews into the chamber and videotaped their response as they turned different jets on and off. They found that the shrews repeatedly attacked brief, sudden water movements designed to simulate disturbances caused by escaping prey.

To test the water shrews’ ability to identify prey by their shape, Catania and his colleagues created fish-shaped silicon objects, mixed them with similarly sized rectangular and cylindrical pieces of silicon and put them in the aquarium with the shrews. Then they observed as the shrews generally ignored the geometric shaped objects but snapped up the fish-shaped targets after nudging them with their whiskers.

The researchers also determined that motion also triggered attacks, even when the moving targets did not have a realistic fish shape. They created moving targets by inserting a small piece of iron into pieces of silicon and used a magnet placed under the tank to make them move.

“One of the difficulties in doing these experiments was that it doesn’t take the shrews long to figure out that our targets are not real fish. You can only fool them a few times,” Catania reports.

David F. Salisbury | EurekAlert!
Further information:
http://www.vanderbilt.edu/exploration/stories/watershrew.html

More articles from Studies and Analyses:

nachricht Innovative genetic tests for children with developmental disorders and epilepsy
11.07.2018 | Christian-Albrechts-Universität zu Kiel

nachricht Oxygen loss in the coastal Baltic Sea is “unprecedentedly severe”
05.07.2018 | European Geosciences Union

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

Computer model predicts how fracturing metallic glass releases energy at the atomic level

20.07.2018 | Physics and Astronomy

Relax, just break it

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>