Diving shrews -- heat before you leap

July 3, 2012
The researchers nicknamed the American water shrews they study the "silver bullet." Credit: Robert A. MacArthur

How does the world's smallest mammalian diver survive icy waters to catch its prey? A recent study of American water shrews to be presented at the Society for Experimental Biology meeting in Salzburg on 1st July has surprised researchers by showing that the animals rapidly elevate body temperature immediately before diving into cold water.

This behaviour is unexpected because lower body temperatures enable diving to stay underwater for longer, so heating up doesn't make sense. This is because animals use up oxygen more quickly when they are warmer.

According to Professor Kevin Campbell of the University of Manitoba, who led the study, "This finding goes against prevailing regarding the physiology of divers. Divers, especially small ones, have always been expected to try to maximize their underwater endurance."

Campbell added that this behaviour indicates the shrews are optimising factors other than just dive duration. Given that they are highly proficient aquatic predators, an elevated body temperature presumably heightens foraging efficiency.

The researchers nicknamed the American water shrews they study the "silver bullet." Credit: Robert A. MacArthur

Large animal divers, like seals and , have been studied extensively, but these findings show that small diving animals deserve attention as well.

Life at the limit

Compared to other diving mammals, the shrews carry the least amount of oxygen under water and use it up the most quickly. Typical dives thus last only 5-7 seconds. Being so small also makes them lose heat the fastest.

Dr Roman Gusztak, who participated in the study, said: "The shrews are likely surviving at the limits of what is possible for a diving mammal. They must continually feed to provide for their voracious appetites but have to contend with very short dive durations and the constant threat of ."

The reaction time of the American water shrew is 10-20 times faster than a human's. Credit: Robert A. MacArthur

Exactly how the shrews warm themselves is unknown. Often, the shrews elevated body temperature while they were simply sitting still at the water's edge before a dive. The researchers believe the shrews are shivering or using their brown fat to generate heat.

As part of this study, the researchers observed the shrews' behaviour when diving into water of different temperatures. They compared the length of the shrews' dives in warm and and also monitored the shrews' before, during, and after dives.

Explore further: How water shrews find prey in the dark

Related Stories

How water shrews find prey in the dark

February 7, 2008

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. The research ...

Sticky snack for elephant-shrews

November 16, 2010

Long-nosed Cape rock elephant-shrews are fond of sticky treats, according to Dr. Petra Wester from the University of Stellenbosch in South Africa. Her investigations show for the first time that the elephant-shrew, Elephantulus ...

Seals protect brain during icy dives

October 10, 2006

Norwegian scientists say they've determined seals cease shivering during long icy dives to conserve oxygen and, therefore, minimize brain damage.

Natural-born divers and the molecular traces of evolution

June 29, 2009

An aquatic lifestyle imposes serious demands for the organism, and this is true even for the tiniest molecules that form our body. When the ancestors of present marine mammals initiated their return to the oceans, their ...

Diving seabirds: Working hard and living long

July 2, 2012

Scientists have found that diving birds reach their 30s and then die quickly and suddenly, showing few signs of aging prior to death. Their findings, which will be presented at the Society for Experimental Biology meeting ...

Recommended for you

What makes tissue soft and yet so tough

November 20, 2017

Engineers at ETH Zurich have discovered that soft biological tissue deforms very differently under tension than previously assumed. Their findings are already being put to use in medical research projects.

The astonishing efficiency of life

November 17, 2017

All life on earth performs computations – and all computations require energy. From single-celled amoeba to multicellular organisms like humans, one of the most basic biological computations common across life is translation: ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.