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 Obstructing the ‘inner eye’
07.07.2017 | Friedrich-Schiller-Universität Jena

nachricht Drone vs. truck deliveries: Which create less carbon pollution?
31.05.2017 | University of Washington

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: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>