MICHEL MARTIN, HOST:
OK, Steve - a question for you.
STEVE INSKEEP, HOST:
OK.
MARTIN: What do penguins, sea turtles and whales have in common?
INSKEEP: They all make cute stuffies for small children in my family.
MARTIN: That could be one thing, OK.
INSKEEP: OK.
MARTIN: But new research suggests they all use the same trick to save energy on marathon swims.
INSKEEP: Got it.
MARTIN: NPR's Jonathan Lambert has more.
JONATHAN LAMBERT, BYLINE: Anyone who's ever swum in open water knows it's hard work. You have to contend with choppy water, and the physical act of swimming creates drag, explains biologist Kimberley Stokes of the University of Swansea in the U.K.
KIMBERLEY STOKES: If an animal swims very close to the surface or at the surface, then they'll be splashing and generally making waves at the surface, which means there's wasted energy because water is being moved without thrusting the animal forwards.
LAMBERT: Diving deeper solves this problem but adds distance, especially because penguins, sea turtles and whales have to come up for air. Theoretically, there should be a sweet spot for swimmers - deep enough to avoid creating waves, but not so deep as to create extra work on journeys that can be hundreds to thousands of miles long. Physics provided a theoretical answer - a depth of about two to three times the diameter or thickness of the body. To test the idea, researchers have turned to some pretty unusual methods.
STOKES: This researcher, Terrie Williams, was dragging frozen carcasses through the water to measure the drag forces and how they changed at different depths. So this kind of sweet spot was predicted previously. But since then, very few people have been able to show examples of animals actually swimming at these depths.
LAMBERT: Stokes teamed up with other researchers who studied the movements of sea turtles, penguins and whales. The team combined data from satellite trackers affixed to turtle shells, video cameras attached to penguins and studies of whale swimming depth.
STOKES: Even though we were comparing animals of really different sizes - the smallest penguin species, only about 30 centimeters long, to pygmy blue whales, around 20 meters long - we found the relative depth - so how deep are they compared to their body size? - was similar across these very different species.
LAMBERT: About two to three times their thickness - just as the physics predicted. The work appears in the journal PNAS.
Jonathan Lambert, NPR News.
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