Washington, Feb 8 : A new study of the water shrew has revealed that the species are highly sophisticated predators, thus challenging the traditional view that the tiny mammals are simple and primitive.
The study reveals remarkably sophisticated methods that the water shrew - an aquatic member of the species, use for detecting prey. These unique hunting methods allow it to catch small fish and aquatic insects as readily in the dark as in daylight.
It is a skill set that is of great importance to the water shrew because of its high metabolism rate, which makes it eat more than its weight daily. If the tiny mammal can't get this daily diet, it can starve to death in half a day.
As a result, water shrews become formidable predators. Water shrews do much of their hunting at night; so I began wondering how they can identify their prey in nearly total darkness," said 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.
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, and, use their sense of smell underwater by blowing air bubbles out of their nose and then re-inhaling them.
"This combination of methods poses a serious conundrum for prey," said Catania. "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," he added.
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 to find prey.
"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," said Catania.