• Scientists reveal secret of a cat's lap

    By Alan Boyle, Science Editor, NBC News

    Engineers have used high-speed videos and mechanical gizmos to figure out the mechanics of a cat's drinking style, confirming what most pet owners know already: Cats are way different from dogs.

    Dogs drink by dipping their tongues into liquids like ladles. A little pool of water is brought into the mouth every time Fido takes a gulp from the toilet bowl. Cats, in contrast, touch only the curled-back tip of the tongue onto the surface of the liquid. When the tongue is drawn back up into the cat's mouth, a thin column of the liquid is drawn up as well. Then the cat closes its mouth around that column.

    The cat-lapping study was published today on the journal Science's website.

    Roman Stocker, an engineering professor at the Massachusetts Institute of Technology who specializes in fluid dynamics, admitted in a Science video interview that the research was "somewhat unusual."

    M. Pilotto, R. Stocker, P. Reis

    How do cats lap? Cutta Cutta shows how it's done.

    "What prompted this study of cats was in fact my cat," he said. "I was watching him one morning, three years ago over breakfast, as he was lapping his water. It occurred to me that there was an exciting biomechanics problem hidden behind the commonplace and apparently simple action of lapping."

    Researchers spent hours at Stocker's house, waiting for the cat (named Cutta Cutta) to take a drink while the high-speed video camera was rolling. They also analyzed scores of videos of drinking cats -- ranging from recordings of big cats at Zoo New England to cute videos they found on YouTube.

    They found that domestic cats average about four laps per second, with each lap bringing in about 0.1 milliliters of liquid. In contrast, tigers, lions and jaguars lap at less than half the rate. In each scenario, the lapping action strikes a balance between the inertia that makes the liquid rise into the cat's mouth ... and the gravity that makes the liquid fall.

    "What is remarkable is that cats seem to know about this balance, and lap with a frequency that maximizes this volume ingested," said MIT's Pedro Reis, another co-author of the paper.

    To tease out the full story behind a cat's lap, the researchers basically used an artificial cat tongue -- a little glass disk attached to the end of a plunger that dipped down onto the surface of a liquid at an adjustable rate. This gave the scientists a way to quantify how gravity and inertia worked together ... without waiting for Cutta Cutta to decide he was thirsty.

    This is the kind of research that sounds as if it came to a conclusion everybody already knows, but Stocker told me these are new discoveries. "I don't think anyone has explained it," he said, "certainly not the balance of forces behind it."

    A lapping cat was one of the subjects covered in the Oscar-winning short subject titled "Quicker 'n a Wink," released back in 1940. MIT engineer Doc Edgerton recorded the cat's technique using a high-speed camera, but didn't delve into the detailed fluid mechanics behind it.

    Stocker admitted that there's not an immediate practical application to the research, which was conducted with borrowed equipment and no outside funding. But he said the mechanics of a cat's tongue could be adapted for robotic devices that move water around using soft structures (like, say, an elephant's trunk). There might also be some evolutionary lessons to be learned from the differences between the drinking habits of cats and dogs.

    The way dogs drink liquids is somewhat messier, Stocker noted. "Part of a cat's face is highly sensitive -- for example, the whiskers. There might be a desire on the part of the cat to keep those dry," Stocker speculated.

    But when you get right down to it, the experiment was "purely curiosity-driven," Stocker said.

    "Although people may not appreciate that, curiosity is often what motivates science," he said. And the nicest part is that in this experiment, curiosity did not kill the cat.

    "The cat is still quite happy," Stocker told me over the telephone. "In fact, he's sitting right beside me now." 

    Update for 2 p.m. ET Nov. 12: Over at the Not Exactly Rocket Science weblog, Ed Yong goes into more detail about the experiment as well as feline drinking habits. He includes a link to "Quicker 'n a Wink" on YouTube -- a link that eluded me yesterday. You can see the cat-drinking footage at around the 4:40 mark in this clip:

    More on cats and dogs:

    In addition to Stocker and Reis, the authors of "How Cats Lap: Water Uptake by Felis Catus" include Virginia Tech's Sunghwan Jung and Princeton's Jeffrey Aristoff.

    Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

  • The 'why' of a leopard's spots

    Cai Priestley

    Patterns like the leopard's rosettes evolve in cats that live in forest habitats.

    Researchers have followed up on Rudyard Kipling's classic tale to investigate why some leopards got their spots — and why others are spotless.

    In one of his "Just-So Stories," Kipling suggested that the leopard scrounged up his distinctive rosettes because he had to stalk his prey undetected in a "great forest, 'sclusively full of trees and bushes and stripy, speckly, patchy-blatchy shadows." Biologists think Kipling wasn't far wrong: The leopard-spot camouflage helps the cats move stealthily through the shadowed forest. But why aren't all big cats spotted?

    Researchers at the University of Bristol have developed a mathematical model that links the patterning of the leopard and 34 other species of wild cats to their different habitats. A paper about their research is being published in the Proceedings of the Royal Society B.

    The model suggests that cats living in the trees within dense habitats, with high activity at low light levels, are the most likely to have complex color patterns in their fur. The cats that spent their time in well-lit and uniform environments, such as plains and grasslands, were more likely to have small spots or plain coats. The analysis supports the view that different patterns of camouflage reflect adaptation to different environments -- and it also suggests that those patterns can change relatively quickly.

    The findings would explain why black leopards (also known as black panthers) are common, while black cheetahs don't exist. As explained in a news release about the research, leopards live in a wide range of habitats ... and some of those habitats offer lighting conditions and behavioral patterns that would favor black leopards over spotted cats. Cheetahs, however, live in a more limited range of habitats.

    The research does raise a few questions, however: The mathematical model generally associates spots with closed environment. But cheetahs are spotted even though they favor open environments, and the bay cat and the flat-headed cat have plain coats despite their preference for closed environments. Why doesn't the model hold true in those cases? (It could be that the cheetah is so fast it doesn't need to rely on camouflage.) And why is the tiger the only species among the 35 studied to have vertically elongated stripes?

    One thing's for sure: The researchers aren't stopping with leopards. Like Kipling, they're gearing up to address other questions of coloration. For example, why do zebras have stripes? Some researchers have suggested that the zebra stripes aren't meant to serve as camouflage, but rather as a cooling system or an insect repellent. Mathematical modeling could provide further evidence for or against such hypotheses.

    "The method we have developed offers insights into cat patterning at many levels of explanation, and we are now applying it to other groups of animals," the University of Bristol's Will Allen said in the news release.

    More about animals and camouflage:

    In addition to Allen, the authors of "Why the Leopard Got Its Spots: Relating Pattern Deveopment to Ecology in Felids" include Innes Cuthill, Nicholas Scott-Samuel and Roland Baddeley.

    Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also check out "The Case for Pluto," Alan's book about the controversial dwarf planet and the search for new worlds.