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by Michael Marshall Anyone who has used an in-car satnav will be familiar with Jane, the calm voice that tells you to turn around because you've gone the wrong way. Many users will also be familiar with the response: yelling "Shut up, Jane!" while performing illegal turns. Bumblebees, it turns out, could give Jane a run for her money. Despite having a brain the size of a poppy seed, these insects can solve a fiendish navigational problem that modern supercomputers struggle to crack. Not so bumbling Bumblebees have been changing their name for centuries. From Shakespeare through to Darwin they were known as "humblebees", because of the humming sound they make. Then in the 20th century, for no good reason, they became "bumblebees". Like honeybees and ants they are social insects, with a queen who controls hordes of sterile workers. Among other ingenious behaviours, they keep their nests at a constant temperatureMovie Camera, avoid foraging close to homeMovie Camera for fear of leading predators to it, and become paranoid when camouflaged predators are aboutMovie Camera. Buff-tailed bumblebee workers fly from flower to flower in search of nectar and pollen. But each flight costs energy and time, so they need to minimise the distance they fly. To do that, they have to solve one of the hardest problems in mathematics: the travelling salesman problem. © Copyright Reed Business Information Ltd.
Gayathri Vaidyanathan Thump! Thump! Thump! As the hollow sound echoes through the Liberian rainforest, Vera Leinert and her fellow researchers freeze. Silently, Leinert directs the guide to investigate. Jefferson 'Bola' Skinnah, a ranger with the Liberian Forestry Development Authority, stalks ahead, using the thumping to mask the sound of his movement. In a sunlit opening in the forest, Skinnah spots a large adult chimpanzee hammering something with a big stone. The chimpanzee puts a broken nut into its mouth then continues pounding. When Skinnah tries to move closer, the chimp disappears into the trees. By the time Leinert and her crew get to the clearing, the animal is long gone. For the past year, Leinert has been trekking through Sapo National Park, Liberia's first and only protected reserve, to study its chimpanzee population. A student volunteer at the Max Planck Institute for Evolutionary Anthropology (EVA) in Leipzig, Germany, Leinert has never seen her elusive subjects in the flesh but she knows some of them well. There's an energetic young male with a big belly who hammers nuts so vigorously he has to grab a sapling for support. There are the stronger adults who can split a nut with three blows. And there are the mothers who parade through the site with their babies. They've all been caught by video cameras placed strategically throughout Sapo. Chimpanzees in the wild are notoriously difficult to study because they flee from humans — with good reason. Bushmeat hunting and human respiratory diseases have decimated chimpanzee populations1, while logging and mining have wiped out their habitat. Population numbers have plunged — although no one knows by exactly how much because in most countries with great apes, the animals have never been properly surveyed. © 2011 Nature Publishing Group,
Link ID: 15690 - Posted: 08.20.2011
Jo Marchant Hyenas can count up to three. Researchers playing recorded calls to the wily carnivores found that wild spotted hyenas (Crocuta crocuta) responded differently depending on whether they heard one, two or three individuals. The result adds numerical assessment to the list of cognitive abilities that hyenas share with primates, and supports the idea that living in complex social groups — as both primates and hyenas do — is key to the evolution of big brains. Sarah Benson-Amram, a zoologist at Michigan State University in East Lansing, and her colleagues played recordings of hyena calls, or whoops, to members of two hyena clans in the Masai Mara National Reserve in southwestern Kenya1. The recordings were made in Tanzania, Malawi and Senegal, so the calls were unfamiliar to the Kenyan clans, and would have been interpreted as belonging to potential intruders. The recordings each consisted of three bouts of whooping, from one, two or three different animals. In 39 trials involving resting adults — mostly lone females — Benson-Amram measured how vigilant the animals became while the recordings were playing by comparing the amount of time they spent facing the speaker with the amount of time they spent looking away or resting. Although some females became equally watchful in response to all of the recordings, most of the animals distinguished between one, two or three intruders, their attentiveness increasing with the number of unique calls they heard. The finding is published in Animal Behaviour. © 2011 Nature Publishing Group,
Link ID: 15689 - Posted: 08.20.2011
By Susan Milius Acts of apparent altruism in European paper wasps can be explained by plain old self-interest, a new study finds. Polistes dominulus females can either establish their own nests to raise young or join other females for joint homemaking. In those joint nests, though, one female fights her way to the top and does most of the egg-laying while the others do most of the drudge work in taking care of the top wasp’s young. When a subordinate helps her sister, that’s not hard to explain: The underling may not end up with her own offspring, but her reproductive success includes an indirect share of her sister’s brood, because relatives share genes. Forgoing her own direct offspring counts as a kind of altruism, in which an individual helping kin trades direct for indirect benefit. Either way, the wasp’s self-interest is served. But some 15 to 35 percent of co-queens slaving away are not closely related to the top wasp, so biologists have been puzzled about why those strangely helpful females don’t go off to found their own nests. They do it because joining an unrelated queen’s nest offers a chance of grabbing the throne, says Ellouise Leadbeater of the Zoological Society of London. She and her colleagues tracked the fortunes of 1,113 foundresses in 228 nests in southern Spain. In this epic population analysis, females that started out as subordinates to a nonrelative occasionally took over the whole nest and laid their own eggs. Their triumphs were rare but dramatic enough so that, overall, the strategy worked out better than being a single mom: Lone nest foundresses hardly managed to produce any offspring, the researchers report in the Aug. 12 Science. © Society for Science & the Public 2000 - 2011
Link ID: 15672 - Posted: 08.13.2011
by Sara Reardon Giving birth to twins is rough, especially in rural regions. They tend to be born smaller and weaker than single babies, and their mothers have more complications during childbirth. So why did twinning evolve? A new study in Gambia finds that women who have twins also tend to have single babies that are heavier than average at birth, which makes them more likely to survive. Since the 1950s, the U.K. Medical Research Council has been collecting data and providing medical care in Gambia. It's a highly unusual data set, says evolutionary anthropologist Rebecca Sear of Durham University in the United Kingdom, with a length and thoroughness that's "unheard of for populations without good access to medical care." Evolutionary biologist Ian Rickard of the University of Sheffield in the United Kingdom wondered whether the data could shed light on the biology of twins. Rickard and colleagues looked at the birth weights of 1889 single babies born to Gambian women over a 30-year period. Then they examined which of these mothers also had twins. Single babies born after twins were 226 grams heavier on average than single babies whose mothers had no twins, the team reports today in Biology Letters. This wasn't surprising, Rickard says, because carrying twins is thought to improve blood flow to the uterus and "prime" it for later children, allowing them to more easily receive nutrients. What did surprise the researchers was the discovery that when single babies were born before twins, the singles tended to be 134 grams heavier than average. © 2010 American Association for the Advancement of Science
By Alexandra Witze There’s just no getting ahead when you’re a hobbit. Anthropologists are arguing yet again over whether a tiny 18,000-year-old Indonesian skull represents a separate species of little human cousins, or an ordinary Homo sapiens with an abnormally small head. New data compare the fossil to a large group of modern humans with microcephaly, a genetic condition that makes the head smaller than usual. Measurements of the hobbit skull suggest its proportions fall within the range of microcephalic Homo sapiens, researchers report August 8 in the Proceedings of the National Academy of Sciences. “Previously published papers that seemed to show that it can’t be a microcephalic are open to doubt,” says coauthor Ralph Holloway, an anthropologist at Columbia University in New York. The hobbit story began in 2003, when archaeologists unearthed the skull and other bones of a female hominid on the island of Flores. Her discoverers argued she represented a member of a human genus that had survived until relatively recently, and dubbed it Homo floresiensis. But some scientists charged that because the hobbit’s skull is so small, it might have just been a microcephalic Homo sapiens. To test that question, anthropologist Dean Falk of Florida State University in Tallahassee compared the skull’s internal dimensions to those of nine microcephalic humans and 10 normal humans. In a 2007 paper, she concluded the hobbit skull was still best assigned to its own species. © Society for Science & the Public 2000 - 2011
Link ID: 15657 - Posted: 08.09.2011
by Helen Fields Despite our wars and crime, humans tend to be nice. We bake for our neighbors, give directions to strangers, and donate money to far-off disaster victims. But does the same go for our closest cousin, the chimpanzee? A new study suggests that it does. People who study chimpanzees in the field have known for a long time that the apes console their comrades when they're upset and support each other in a fight. And when one chimp has a good hunting day and kills a nice, juicy monkey, it shares the meat with the other members of its group. But scientists have found that chimps don't share in lab experiments, creating a bit of a primatology mystery. For instance, when researchers gave captive chimps the opportunity to get rewards just for themselves or for both themselves and another chimpanzee from an apparatus with multiple interconnected trays, the apes were equally likely to choose the selfish and sharing options. Comparative psychologist Victoria Horner of Emory University in Atlanta thought she knew the reason why experiments didn't find sharing: the experimental setups other scientists used to test the chimps were just too confusing—"tables with pulley systems and whatnot." For one study, she says, "I had to read it several times before I understood the apparatus, and I'm a human." She thinks the chimps didn't understand how what they did affected their partner. With her colleagues at Emory, including renown primatologist Frans de Waal, Horner devised a new way to test chimps' generosity. "We did the same basic idea but from a more chimpy perspective," she says. In each experiment, two female chimps that live at the Yerkes National Primate Research Center in Lawrenceville, Georgia, were put in side-by-side rooms with a mesh-covered opening between them. Both chimps had been trained to "buy" food from the researchers with tokens, colored, 5-centimeter-long pieces of PVC pipe. © 2010 American Association for the Advancement of Science.
by Helen Fields Humans buy unripe bananas, then leave them on the kitchen counter. The tayra, a relative of the weasel native to Central and South America, appears to do much the same thing, picking unripe plantains and hiding them until they ripen, according to a new study. The authors speculate that tayras are showing a human-like capacity to plan for the future, which has previously been shown only in primates and birds. Biologist Fernando Soley was an undergraduate at the University of Costa Rica in 2004 when he first started thinking about tayras. He was studying poison dart frogs at La Selva Biological Station in northern Costa Rica, when he noticed a tayra—essentially a giant weasel with a bushy tail—approach a tree. "It climbed 4 meters high, went directly to a bromeliad [a plant growing in the tree], and came back down with a ripe plantain and ate it," Soley says. The trees in the forestry plantation where he was working are planted in neat rows, and it's easy for humans to get lost. Because the animal went straight to the plantain, he thought it couldn't have found it by chance. "I thought, wow, for sure this animal was the one that brought it there." A few years later, Soley came back for a closer look at the tayras, teaming up with Isaías Alvarado-Díaz, a self-taught biologist who lives near La Selva. Animals don't spend much time in the forestry plantation, so Soley thought tayras might hide their fruit there to keep it safe from prying snouts. The duo set up an Easter egg hunt for fruit thieves to find out if the tayras were doing a good job. "We hid pieces of banana, which pretty much tastes and smells very similar to plantains, in the forest and in the plantation, and after 2 days we went to count them," he says. Animals found fewer bananas in trees than on the ground, and fewer in the plantation than in the forest. That means hiding plantains in the plantation and up in tree is a smart move by tayras that don't want other animals to find their treasures. © 2010 American Association for the Advancement of Science
By Victoria Gill Science reporter, BBC Nature The flamboyant "booming" display of the threatened Houbara bustard is linked to the rate at which the birds age A large, flamboyant bird has given biologists an insight into the relationship between sex and ageing. The male Houbara bustard has striking ornamental feathers that it displays while running around and "booming" to attract a mate. As scientists report in Ecology Letters, birds that indulge in more of these sexual displays age faster. The more "showy" males experienced earlier age-related declines in the quality of their sperm. The team used 10-years-worth of data on the sexual behaviour and fertility of more than 1,700 North African Houbara bustards that were bred by conservationists in Missour, Morocco. "The birds are a threatened species, and the data was collected as part of an ongoing conservation programme aimed at increasing their numbers in the wild," explained lead researcher Brian Preston, a scientist based at the University of Burgundy, France. The scientists measured how much time each male spent carrying out its elaborate display, and compared this to changes in its fertility that are associated with ageing. BBC © 2011
THE extraordinary success of Homo sapiens is a result of four things: intelligence, language, an ability to manipulate objects dexterously in order to make tools, and co-operation. Over the decades the anthropological spotlight has shifted from one to another of these as the prime mover of the package, and thus the fundament of the human condition. At the moment co-operation is the most fashionable subject of investigation. In particular, why are humans so willing to collaborate with unrelated strangers, even to the point of risking being cheated by people whose characters they cannot possibly know? Evidence from economic games played in the laboratory for real money suggests humans are both trusting of those they have no reason to expect they will ever see again, and surprisingly unwilling to cheat them—and that these phenomena are deeply ingrained in the species’s psychology. Existing theories of the evolution of trust depend either on the participants being relatives (and thus sharing genes) or on their relationship being long-term, with each keeping count to make sure the overall benefits of collaboration exceed the costs. Neither applies in the case of passing strangers, and that has led to speculation that something extraordinary, such as a need for extreme collaboration prompted by the emergence of warfare that uses weapons, has happened in recent human evolution to promote the emergence of an instinct for unconditional generosity. Leda Cosmides and John Tooby, two doyens of the field, who work at the University of California, Santa Barbara, do not agree. They see no need for extraordinary mechanisms and the latest study to come from their group (the actual work was done by Andrew Delton and Max Krasnow, who have just published the results in the Proceedings of the National Academy of Sciences) suggests they are right. It also shows the value of applying common sense to psychological analyses—but then of backing that common sense with some solid mathematical modelling. © The Economist Newspaper Limited 2011.
Link ID: 15642 - Posted: 08.04.2011
By SINDYA N. BHANOO The Marcgravia evenia plant has dish-shaped leaves that bounce back echoes that bats can identify through echolocation. The vine, Marcgravia evenia, has dish-shaped leaves that bounce back echoes that are easy for the bats to identify through echolocation. “They have a very special kind of echo,” said the lead author, Ralph Simon, a biologist at the University of Ulm in Germany. “This echo is very loud and has a constant signature from different angles.” Dr. Simon and his colleagues trained bats in the laboratory to look for a feeder. They then placed it in different locations — attached to a dish-shaped leaf, an ordinary leaf or no leaf. The bats located the feeder in half the time when it was attached to a dish-shaped leaf. And that was good for the bats and the vine. “For the plants, it increases the success of pollination,” Dr. Simon said. “For the bats, it’s good because it helps them find the flowers faster — they have to make several hundred visits to flowers every night.” The study, which appears in the current issue of the journal Science, is one of the first to focus on the evolution of echo-acoustic signals in plants. Several hundred species of plants in the Neotropics rely on about 40 nectar-feeding bat species for pollination, Dr. Simon said. © 2011 The New York Times Company
by Michael Balter "This town ain't big enough for the both of us," says ranch foreman Nick Grindell to lawman Tim Barrett in the 1932 film The Western Code. Biologists know the principle well: Two animal species can rarely occupy the same niche. The same, it seems, goes for human populations. A new study of Neandertal and modern human sites in the south of France concludes that the moderns so greatly outnumbered their evolutionary cousins that Neandertals had little choice but to go extinct. For more than 100,000 years, Neandertals had Europe all to themselves. Then, beginning roughly 40,000 years ago, modern humans—Homo sapiens—began migrating into the continent from Africa. Although researchers debate how long the Neandertals hung around, these ancient humans probably did not survive much longer than 5000 years. Just why they disappeared is also a matter of contention, but most experts agree that H. sapiens was able to outgun its rival in either direct or indirect competition for food and other resources. Some genetic studies, based on both modern and ancient DNA sequences, have suggested that modern human population growth quickly outstripped that of Neandertals, but estimating population levels from these kinds of data is very difficult and inexact. So Paul Mellars and Jennifer French, archaeologists at the University of Cambridge in the United Kingdom, decided to look directly at the archaeological evidence for the presence of both groups in the region where the most excavations have taken place: southwestern France, including the lush Dordogne region, as well known for its prehistoric sites as for its wine and foie gras. © 2010 American Association for the Advancement of Science
Link ID: 15625 - Posted: 07.30.2011
by Carl Zimmer In 1758 the Swedish taxonomist Carolus Linnaeus dubbed our species Homo sapiens, Latin for “wise man.” It’s a matter of open debate whether we actually live up to that moniker. If Linnaeus had wanted to stand on more solid ground, he could have instead called us Homo megalencephalus: “man with a giant brain.” Regardless of how wisely we may use our brains, there’s no disputing that they are extraordinarily big. The average human brain weighs in at about three pounds, or 1,350 grams. Our closest living relatives, the chimpanzees, have less than one-third as much brain—just 384 grams. And if you compare the relative size of brains to bodies, our brains are even more impressive. As a general rule, mammal species with big bodies tend to have big brains. If you know the weight of a mammal’s body, you can make a fairly good guess about how large its brain will be. As far as scientists can tell, this rule derives from the fact that the more body there is, the more neurons needed to control it. But this body-to-brain rule isn’t perfect. Some species deviate a little from it. A few deviate a lot. We humans are particularly spectacular rule breakers. If we were an ordinary mammal species, our brains would be about one-sixth their actual size. Competing theories seek to explain the value of a big brain. One idea, championed by psychologist Robin Dunbar of the University of Oxford, is that complicated social lives require big brains (pdf). A relatively large-brained baboon can make a dozen alliances while holding grudges against several rivals. Humans maintain far more, and more complicated, relationships. © 2011, Kalmbach Publishing Co.
Link ID: 15623 - Posted: 07.28.2011
By Judith Burns Science reporter, BBC News Humans living at high latitude have bigger eyes and bigger brains to cope with poor light during long winters and cloudy days, UK scientists have said. The Oxford University team said bigger brains did not make people smarter. Larger vision processing areas fill the extra capacity, they write in the Royal Society's Biology Letters journal. The scientists measured the eye sockets and brain volumes of 55 skulls from 12 populations across the world, and plotted the results against latitude. Lead author Eiluned Pearce told BBC News: "We found a positive relationship between absolute latitude and both eye socket size and cranial capacity." The team, from the Institute of Cognitive and Evolutionary Anthropology, used skulls dating from the 1800s kept at museums in Oxford and Cambridge. The skulls were from indigenous populations ranging from Scandinavia to Australia, Micronesia and North America. Largest brain cavities The largest brain cavities came from Scandinavia, while the smallest were from Micronesia. BBC © 2011
Link ID: 15619 - Posted: 07.28.2011
by Virginia Morell Asian elephants have long been considered somewhat antisocial. Instead of living in large, tightly knit herds, as do female elephants on the African savanna, those in Asia were thought to have only small groups of friends and few outside connections. But a new study shows that many female Asian elephants are more like social butterflies, with numerous pals. And they're able to maintain strong friendships even with those they have not seen in a year or more. The study adds Asian elephants to a short list of other species, including dolphins, that are able to maintain complex social relationships despite not having daily contact, an ability regarded as being cognitively demanding. "People thought they knew what Asian elephants were doing [socially] based on what they saw them doing in captivity," says Shermin de Silva, a behavioral ecologist with the Elephant, Forest and Environment Conservation Trust in Colombo, Sri Lanka, and the lead author of the new study. Asian elephants are also extremely difficult to study in the wild, she adds. They inhabit dense forests, so researchers are usually able to observe the animals only by climbing tall trees or watching them when they gather at water holes. But 30 years ago, one population of Asian elephants on Sri Lanka became observable because it lost its forest home. People logged the trees, converted the land into teak plantations, and subsequently dammed the region's main river, creating the large Uda Walawe reservoir. In 1972, 308 square kilometers around the reservoir were made into the Udawalawe National Park. Some 800 to 1200 former forest elephants now live here on grass- and scrublands that resemble an East African savanna, de Silva says. © 2010 American Association for the Advancement of Science.
Link ID: 15613 - Posted: 07.28.2011
By Laura Sanders Unlike humans, chimpanzees’ brains don’t shrink as they get older. That means that, so far, people seem to be the only lucky species whose brains wither with age, researchers report online July 25 in the Proceedings of the National Academy of Sciences. “Chimp aging seems to be on a different trajectory than humans’,” says aging and Alzheimer’s expert Caleb Finch of the University of Southern California in Los Angeles, who was not involved in the study. So far, the small number of great ape brains that have been studied show mild changes with age, Finch says, but nothing that approaches the damage seen in the brains of people with Alzheimer’s disease. Understanding differences in aging between humans and other primates may help scientists figure out why human brains are susceptible to age-related dementias. In the new study, anthropologist Chet Sherwood of George Washington University in Washington, D.C., and colleagues focused on chimpanzees, which have some of the most developed brains and longest life spans among primates. The researchers wondered if chimps experience brain decline in old age similar to that seen in humans. The researchers scanned the brains of 99 chimpanzees with ages representing the entire adult life span, from 10 to 51 years. For comparison, the team imaged the brains of 87 humans from 22 to 88 years old. © Society for Science & the Public 2000 - 2011
Analysis by Kieran Mulvaney Whale-watching tourists off western Australia saw more than they expected - and perhaps more than many of them wanted - last week. As two boats of observers took in the action, a humpback whale mother desperately and vainly tried to protect a calf from four predatory orcas. The video below, shot from a light aircraft that circled overhead as the action unfolded, isn't always easy to make out, but it shows the orcas circling as the humpback attempts to protect the calf by lifting it on to her back. (If you pause the video at about 12 seconds, you can see the whale more or less center of the screen, and the lighter-colored calf just above it.) According to witnesses, the humpback was spotted with two calves, but the orcas swiftly came on the attack taking one. The mother only succeeded in protecting her second calf for about three-quarters of an hour before it, too, succumbed to the ambush: "I've been diving for three years and I've never seen anything like it," said Tamar Melen, who watched the 45-minute spectacle unfold metres from the boat. Sadly, the killer whales made off with both calves. Ms Melen, 31, said they grabbed the first in seconds, but the attack on the second lasted half an hour. "It was quite impressive," Ms Melen said. "The first hit was so quick, but then they took their time with the second. It was agonising to watch the mother humpback trying to protect her calf. © 2011 Discovery Communications, LLC.
By CARL ZIMMER To study evolution, Jason Munshi-South has tracked elephants in central Africa and proboscis monkeys in the wilds of Borneo. But for his most recent expedition, he took the A train. Dr. Munshi-South and two graduate students, Paolo Cocco and Stephen Harris, climbed out of the 168th Street station lugging backpacks and a plastic crate full of scales, Ziploc bags, clipboards, rulers and tarps. They walked east to the entrance of Highbridge Park, where they met Ellen Pehek, a senior ecologist in the New York City Parks and Recreation Department. The four researchers entered the park, made their way past a basketball game and turned off the paved path into a ravine. They worked their way down the steep slope, past schist boulders, bent pieces of rebar, oaks and maples, hunks of concrete and freakish poison ivy plants with leaves the size of a man’s hands. The ravine flattened out at the edge of Harlem River Drive. The scientists walked north along a guardrail contorted by years of car crashes before plunging back into the forest to reach their field site. “We get police called on us a lot,” said Dr. Munshi-South, an assistant professor at Baruch College. “Sometimes with guns drawn.” Dr. Munshi-South has joined the ranks of a small but growing number of field biologists who study urban evolution — not the rise and fall of skyscrapers and neighborhoods, but the biological changes that cities bring to the wildlife that inhabits them. For these scientists, the New York metropolitan region is one great laboratory. © 2011 The New York Times Company
Link ID: 15602 - Posted: 07.26.2011
By Katherine Harmon Just like our animal skin–clad ancestors, we gather food with zeal, lust over the most capable mates, and have an aversion to scammers. And we do still wear plenty of animal skins. But does more separate us from our Stone Age forebears than cartoonists and popular psychologists might have us believe? At first blush, parsing the modern human in terms of behaviors apparently hardwired into the brain over eons of evolution seems like a tidy, straightforward exercise. And 30 years ago, when the field of evolutionary psychology was gaining steam, some facile parallels between ancient and modern behaviors lodged themselves in the popular conceptions of human evolution. "It's very easy to slip into a very simplistic view of human nature," says Robert Kurzban, an associate professor of psychology at the University of Pennsylvania, citing the classic Flintstones stereotype. Advances in neuroscience and genetics now suggest that the human brain has changed more rapidly—and in different ways—than was initially thought, according to a new paper published online July 19 in PLoS Biology. "There's been a lot of recent evolution—far more than anyone envisioned in the 1980s when this idea came to prominence," says Kevin Laland, a professor at the University of Saint Andrew's School of Biology in Scotland and co-author of the new paper. He and his colleagues argue that today's better understanding of the pace of evolution, human adaptability and the way the mind works all suggest that, contrary to cartoon stereotypes, modern humans are not just primitive savages struggling to make psychological sense of an alien contemporary world. © 2011 Scientific American
Link ID: 15587 - Posted: 07.21.2011
by Virginia Morell In 1991, researchers spotted dolphins doing something unusual in Shark Bay, Western Australia. When the animals got hungry, they ripped a marine basket sponge from the sea floor and fitted it over their beaks like a person would fit a glove over a hand. The scientists suspected that as the dolphins foraged for fish, the sponges protected their beaks, or rostra, from the rocks and broken chunks of coral that litter the sea floor, making this behavior the first example of tool use in this species. But why do dolphins go to all of this trouble when they could simply snag a fish from the open sea? The answer, researchers report online today in PLoS ONE, is that the bottom-dwelling fish are a lot more nutritious. Some species also don't have swim bladders, gas chambers that help other fish control their buoyancy as they travel up and down the water column. In the Bahamas, where dolphins are also known to forage for bottom-dwelling fish, dolphins hunt partly by echolocating these bladders, which give off a strong acoustic signal. That helps the cetaceans find prey even when it's buried in sea sand. But bottom-dwelling fish, such as barred sandperch, which are favored by some Shark Bay dolphins, don't have swim bladders and so are harder to find with echolocation. The sea floor is not nearly as soft here as it is in the Bahamas, so if dolphins want to probe for these fish, they risk injuring their rostra. © 2010 American Association for the Advancement of Science
Link ID: 15586 - Posted: 07.21.2011