Chapter 6. Evolution of the Brain and Behavior
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By PAUL VITELLO Alison Jolly, an American-born primatologist whose research in the forests of Madagascar shed new light on the evolution of social intelligence and helped disprove a longstanding scientific tenet that males were dominant in every primate species, died on Feb. 6 in Lewes, East Sussex, England. She was 76. The cause was breast cancer, said Barbara Orlando, a longtime friend. Dr. Jolly’s two major insights emerged from her 1960s field studies of the lemur, a primate whose development in relative isolation on the island of Madagascar makes the species something akin to a living fossil. Dr. Jolly cited lemurs’ complex social relationships as evidence of an unexplored trail in one of anthropology’s great mysteries: the evolution of higher intelligence. Writing in the journal Science in 1966, she suggested that the many hours lemurs spent in play, mutual grooming and social networking — activities that establish the social ties and hierarchies that determine access to food, mate selection and migration patterns — may have been as important to the evolution of intelligence as the development of weapons and tools of hunting and protection, then considered the hallmarks of evolutionary advance. More unnerving to colleagues was her discovery that in some primate species, females run the show. The finding upended a bedrock assertion in evolutionary biology — based on studies of chimpanzees and orangutans in captivity — that males dominated females in every primate species, including humans. “Females have social, spatial and feeding priority over males,” Dr. Jolly wrote in describing the feeding, mating, child-rearing and recreational habits of the ring-tailed lemur, one of about 100 recognized species of lemur, of which more than a dozen are female-dominant. Among the ring-tailed lemurs, Dr. Jolly wrote in “Lemur Behavior: A Madagascar Field Study,” “all females, whether dominant or subordinate in the female hierarchy, are dominant over males.” © 2014 The New York Times Company
Elephants, both African and Asian, have long been considered empathetic animals. They help baby elephants stuck in mud holes, use their trunks to lift other elephants that are injured or dying, and even reportedly reassure distressed individual elephants with a gentle touch of their trunk. But it’s one thing to witness something that looks like consolation, and another to prove that this is what elephants are doing. Now, scientists have shown that African elephants do indeed get distressed when they see others in trouble, and they reach out to console them—just as we do when we see someone suffering. Elephants, thus, join a short list of other animals, including great apes, canines, and some birds, that scientists have shown to reassure others. The study “is the first to investigate responses to distress by Asian elephants,” which “is inherently difficult to assess because one has to wait for opportunities to arise spontaneously,” says Shermin de Silva, an behavioral ecologist at the Uda Walawe Elephant Research Project in Sri Lanka. It would not be ethical to intentionally create stressful situations for the animals as a test, she notes—which is why, until now, researchers have had to rely on well-documented, but anecdotal observations of wild and captive elephants to back up claims that they reassure each other. Joshua Plotnik, a behavioral ecologist at Mahidol University in Kanchanaburi, Thailand, and Frans de Waal, a primatologist at Emory University, got around this problem by comparing Asian elephants’ behaviors during times of stress to periods when little upset them. For one to two weeks every month for nearly a year, Plotnik spent 30 to 180 minutes daily watching and recording 26 captive Asian elephants. The animals ranged in age from 3 to 60 years old and lived at the 30-acre Elephant Nature Park in northern Thailand. Most of the elephants, aside from mother-juvenile pairs, were unrelated, and did not live in family groups as wild elephants do. Instead, the park’s Mahouts, or keepers, organized them into six groups which they then guided through a daily routine—bathing and feeding them in the morning, and tethering them at night. But during the day, the elephants were left alone to roam and graze at will. © 2014 American Association for the Advancement of Science
It seems simple: People are more likely to cooperate if everyone plays fair. But a new study suggests that fairness itself arises from an unlikely source: spite. Researchers made a mathematical model based on the so-called ultimatum game. In it, two players are offered a reward, and the first player makes an offer for how it should be split up. If the second player agrees, then they divide it accordingly. But if the second player refuses, then neither gets the reward. As shown in the image above, depending on the interaction of the players, the outcome can be classified as altruism, cooperation, selfishness, or spite. Previous experiments have shown that, over multiple rounds of the game, a culture of cooperation evolves where everyone makes fair offers. But the new study, published online today in the Proceedings of the Royal Society B, finds that when players start out using multiple different strategies, by making fair or unfair offers, and rejecting or accepting unfair offers, some will act out of spite. These spiteful players deny the first player the reward at a cost to himself. The calculations further show that the antisocial behavior will eventually cause fairness to become the most successful option, because there is no reason to reject a fair offer. In essence, fairness evolves in spite of spite, when players start out using different strategies. Though they warn against generalizing to humans, the researchers point out that if fairness is the basis for a moral society, then paradoxically, spite may have played a role in the evolution of morality. © 2014 American Association for the Advancement of Science.
| by Isaac Saul Multi-step puzzles can be difficult for humans, but what if I told you there was a bird that could solve them on its own? In this BBC special, Dr. Alex Taylor has set up an eight-step puzzle to try and stump one of the smartest crows he's seen in captivity. They describe the puzzle as "one of the most complex tests of the animal mind ever." This isn't the first time crows' intelligence has been tested, either. Along with being problem solvers, these animals have an eerie tendency towards complex human-like memory skills. Through several different studies, we've learned that crows can recognize faces, communicate details of an event to each other and even avoid places they recognize as dangerous. This bird, dubbed "007" for its crafty mind, flies into the caged puzzle and spends only seconds analyzing the puzzle before getting down to business. Despite the puzzle's difficulty, the bird only seems to be stumped momentarily. At the end of the puzzle is a food reward, but how he gets there is what will really blow your mind. © 2014 TheHuffingtonPost.com, Inc
By Matt McGrath Environment correspondent, BBC News Successful professional cyclists are seen as more handsome than their struggling colleagues, according to new research. Women rated facial attractiveness among riders in the 2012 Tour de France, won by Britain's Sir Bradley Wiggins. The top 10% of performers were rated on average as 25% better looking than the laggards. The scientists conclude that humans have evolved to recognise athletic performance in faces. The research has been published in the Royal Society journal, Biology Letters. Some biologists argue that evolution has shaped women to select mates on the basis that they would either make good fathers or would pass on good genes. Healthy, physically fit men would on average be seen as more attractive by women. A number of other studies in recent years have suggested that women have a sophisticated radar for athletic performance, rating those with greater sporting skill as more attractive. This new work, though, set out to test if the same applied to more inherent physical qualities such as stamina and endurance. Cycle of life Dr Erik Postma, from the Institute of Evolutionary Biology at the University of Zurich, asked people to rate the attractiveness of 80 professional cyclists from the 2012 Tour de France. The cyclists were all of a similar physical stature, were tanned and around the same age. BBC © 2014
Alice Roberts Just how special do you think you are? How different do you think you are from other animals? Do you think of yourself as an animal or do you see yourself, and your fellow humans, as somehow set apart from the rest of the animal kingdom? Most of us – and I would unashamedly label us as the sensible majority of the population – accept that evolution is the best explanation for the pattern of life that we observe on the planet, both living and fossilised. However much creationists bang on about evolution being "just a theory", it beautifully explains all the evidence we have to hand (and there's masses of that: anatomical, genetic, palaeontological, embryological), without a single piece of evidence having turned up that threatens to bring the whole edifice tumbling down around our ears. So, I'm hoping you're a sensible sort of person and that you consider evolution to be as true as the spherical nature of the Earth, or the fact that the Earth orbits the sun and not vice versa. But just how comfortable are you with the idea of being a product of evolution? I think it's still, even among the most enlightened of us, really hard to come to terms with the idea that we are just another animal. A naked ape. The third chimpanzee, even. You have to admit, science has done a very good job at bringing us down a peg or two, at knocking us off the pedestal of our own construction. We can no longer view ourselves as a special creation, something created in the image of a deity and close to angels (whatever they are or look like). We can no longer see ourselves as the ultimate destination, as the pinnacle of evolution, either. Our species is just a tiny twig on the massive, dense tree of life. But that's so difficult to stomach! © 2014 Guardian News and Media Limited
By Meeri Kim, Neanderthal genes lurk among us. Small traces of Neanderthal DNA have been confirmed in the areas of the genome that affect skin and hair of modern humans, according to two new studies that also give clues as to which Neanderthal traits may have been helpful — or harmful — to the survival of our species. The studies, published online Wednesday in the journals Nature and Science, came to similar conclusions despite using vastly different methods of genomic analysis. For East Asian and European populations, genes that provide the physical characteristics of skin and hair have a high incidence of Neanderthal DNA — possibly lending toughness and insulation to weather the cold as early man emerged from Africa, the studies conclude. Neanderthals were thought to have already been adapted to a chillier, more northern environment. Perhaps most notably, Neanderthal DNA was not found in genes that influence testicles or the X chromosome, according to the Nature study, hinting that when the Neanderthal ventured outside his species for sex, the introduction of his DNA may have reduced male fertility in early humans. As a result, evolution wiped away the Neanderthal DNA that negatively affected procreation. “There’s strong evidence that when the two met and mixed, they were at the edge of biological compatibility,” said Nature study author and Harvard University geneticist David Reich. “The people who eventually survived and thrived had quite a bit of hurdles to overcome.” This is consistent with what is seen in nature: When two species mate that are sufficiently far away biologically, the resulting hybrids tend to have lowered fertility. Early humans and Neanderthals interbred about 40,000 to 80,000 years ago around the Middle East, during man’s migration out of Africa. © 1996-2014 The Washington Post
by Susan Milius Male bee flies fooled into trying to copulate with a daisy may learn from the awkward incident. Certain orchids and several forms of South Africa’s Gorteria diffusa daisy lure pollinators by mimicking female insects. The most effective daisy seducers row a dark, somewhat fly-shaped bump on one of their otherwise yellow-to-orange petals. Males of small, dark Megapalpus capensis bee flies go wild. But tests show the daisy’s victims waste less time trying to mate with a second deceptive daisy than with the first. “Far from being slow and stupid, these males are actually quite keen observers and fairly perceptive for a fly,” says Marinus L. de Jager of Stellenbosch University in South Africa. Males’ success locating a female bee fly drops in the presence of deceitful daisies, de Jager and Stellenbosch University colleague Allan Ellis say January 29 in the Proceedings of the Royal Society B. That’s the first clear demonstration of sexual deceit’s cost to a pollinator, Ellis says. Such evolutionary costs might push the bee fly to learn from mating mistakes. How long bee flies stay daisy-wary remains unknown. In other studies, wasps tricked by an Australian orchid forgot their lesson after about 24 hours. © Society for Science & the Public 2000 - 2014
by Ashley Yeager Monkeys may have rudimentary brain wiring that later evolved into the connections that gave humans the ability to understand language, think flexibly and make decisions. Brain scans of 25 humans and 25 macaques show that 11 components of the ventrolateral frontal cortex, located behind the temples, were similarly wired in both species. The results suggest that humans did not develop completely new and specialized brain systems for certain types of complex thought, researchers report January 28 in Neuron. The scans also show that macaques do not have the lateral frontal pole, which helps humans with strategic planning, decision-making and multitasking. © Society for Science & the Public 2000 - 2014.
Link ID: 19184 - Posted: 01.30.2014
by Erika Engelhaupt Twerking is so 50 million years ago. In fact, it’s probably much older than that. Today, the provocative, butt-shaking dance move is enough of a social phenomenon to merit a word in the dictionary (with twerking defined about as tastefully as possible here by actor Morgan Freeman), but animals have been shaking their hindquarters for ages, for a variety of purposes (more on that below). Black widow spiders are the latest documented twerkers. In their case, it’s the males that shake their rears. Black widow females are aggressive predators and will immediately kill any prey detected in their webs. This presents a problem for males approaching a female to mate; in this case a literal misstep means becoming the female’s dinner. To figure out how the males avoid being eaten (at least before mating), researchers at Simon Fraser University in Canada measured vibrations created by males and by prey in webs of western black widows (Latrodectus hesperus). They compared the vibrations, and the females’ responses, to those of the hobo spider (Tegenaria agrestis), a species in which females rarely attack courting males. To capture the details of small vibrations, they used a fun tool called a laser Doppler vibrometer, which measures small changes in a laser beam aimed at a surface. Sure enough, black widow males appeared to have a death-avoidance strategy. They produced vibrations different from thrashing prey by means of “lengthy andrepeated bouts of abdominal tremulations” averaging 43 wiggles per second, the researchers report January 17 in Frontiers in Zoology. You can see a male's moves in this video: © Society for Science & the Public 2000 - 2014
Things are heating up in the world of genetics. The hot pepper (Capsicum annuum) is one of the most widely grown spice crops globally, playing an important role in many medicines, makeups, and meals worldwide. Although the plant’s so-called capsaicin chemical is well known for spicing things up, until now the genetic spark responsible for the pepper’s pungency was unknown. A team of scientists recently completed the first high-quality reference genome for the hot pepper. Comparing the pepper’s genome with that of its tame cousin, the tomato, the scientists discovered the gene responsible for fiery capsaicin production appeared in both plants. While the tomato carried four nonfunctioning copies of the gene, the hot pepper carried seven nonfunctioning copies and one functioning copy, the team reports online today in Nature Genetics. The researchers believe the pepper’s capsaicin-creating gene appeared after five mutations occurred during DNA replication, with the final mutation creating a functional copy. The mouth-burning chemicals likely protected the mutant pepper’s seeds from grazing land animals millions of years ago, giving the mutant a reproductive advantage and helping the mutant gene spread. The team says the finding could help breeders boost the pepper’s heat, nutrition, and medicinal properties. One researcher even suggests that geneticists could activate one of the tomato’s dormant genes, enabling capsaicinoid production and creating a plant that makes ready-made salsa. © 2014 American Association for the Advancement of Science.
Imagine a couple of million years ago, a curious young alien from the planet Zantar — let's call him a grad student — lands on Earth, looks around and asks, "Who's the brainiest critter on this planet? Relative to body size, who's got the biggest brain?" The answer, back then, would not have been us. (Two million years ago, apes — even walking ones — had much smaller brains.) The brainiest weren't ancestral crows or parrots or magpies or ravens or elephants or colonies of ants or bees or termites. The Earthlings with the biggest brains back then were dolphins (and certain whales). The Zantarian grad student would have wanted to meet them. A visitor from Zantar and a dolphin check each other out. But had the grad student arrived earlier, dolphins wouldn't have been the champs, because evolution is always changing life. , at Emory University in Atlanta, has been studying fossilized brains. And looking back, she sees sudden spurts of brain growth in different animals. "[T]he most dramatic increase in brain-to-body ratio in dolphins and toothed whales occurred 35 million years ago," she tells Chris Impey, the astronomer and writer, in Talking About Life. Something happened to make their medium-sized brains bigger, Lori says, then bigger still. For 20 million years certain dolphin species kept their brains growing until — just as mysteriously as it started — about 15 million years ago, they stopped. Why? Had the dolphins answered some secret dolphin question? Figured out a puzzle? Adapted to an environmental change? Gotten tired? Hit a limit? What? Dolphin says, "Enough." ©2014 NPR
By Felicity Muth Whether there exist differences between boys and girls is passionately debated (for example, see this debate about gender disparity between Stephen Pinker and Elizabeth Spelke). Some studies have found that girls are more sociable than boys, but prefer to play with just one other person, while boys prefer a larger group to play with. However, it is very difficult to say whether differences that we see in boys’ and girls’ behaviour has a biological basis, as boys and girls are also treated differently. Even before a baby is born, parents have often painted its room pink or blue, and bought gender-differentiated toys. A mother is more likely to under-estimate her female baby’s crawling abilities, and over-estimate her male baby’s (he’s a boy, of course he’s going to be stronger and better at crawling?!). Perceptions on the personality and abilities of a baby also differ depending on whether the adult is told that the child is male or female. Given these differences in how people treat male and female children, it can be difficult to say whether the behaviours we see are have a biological basis or not. However, we can look for certain clues to biological differences in child behaviour from our ‘cousins’ the chimpanzees. Chimpanzees live in communities of 20 to 180 individuals, with sub-groups within this. One recent study looked at the behaviour of eight female and twelve male chimpanzee infants to see if their behaviour differed from each other. They found that the young males were more sociable than the young females. © 2014 Scientific American
Ed Yong A marine iguana (Amblyrhynchus cristatus) at the Galapagos Islands National Park rests calmly as tourists walk by — a behaviour that may have evolved because of a lack of predators. Expand When Charles Darwin visited the Galapagos Islands, he noted that many of its animal inhabitants were so unafraid of people that “a gun is here almost superfluous”. He swatted birds with his hat, pulled the tails of iguanas and sat on giant tortoises. These antics fuelled his famous idea that animals become tame when they live on remote, predator-free islands. Now, William Cooper Jr of Indiana University–Purdue University in Fort Wayne has tested Darwin's hypothesis on 66 species of lizards from around the world and found that island dwellers tended to be more docile than their continental relatives — the strongest evidence yet for this classic idea. The results are published this week in Proceedings of the Royal Society B1. Several studies and unpublished reports have shown that particular species are more approachable on islands where there are fewer predators, or quicker to flee on islands that contain introduced hunters such as feral cats. But despite this largely anecdotal evidence for island tameness, “no one has ever established that it’s a general phenomenon in any group”, says Cooper. “We showed that for a large prey group — lizards — there really is a significant decline in wariness on islands.” © 2014 Nature Publishing Group
By GRETCHEN REYNOLDS African tribesmen walk through their landscape in a pattern that eerily echoes the movements of scavenging birds, flocking insects, gliding sharks and visitors to Disneyland, a new study finds, suggesting that aspects of how we choose to move around in our world are deeply hard-wired. For the new study, which appeared online recently in Proceedings of the National Academy of Sciences, researchers at the University of Arizona at Tucson, Yale University, the New York Consortium in Evolutionary Primatology and other institutions traveled to northern Tanzania to study the Hadza, who are among the last human hunter-gatherers on earth. The Hadza generally spend their days following game and foraging for side dishes and condiments such as desert tubers and honey, frequently walking and jogging for miles in the process. The ways in which creatures, including people, navigate their world is a topic of considerable scientific interest, but one that, until the advent of global positioning systems and similar tracking technology, was difficult to quantify. In the past decade, however, scientists have begun strapping GPS units to many varieties of animals and insects, from bumblebees to birds, and measuring how they move. What they have found is that when moving with a purpose such as foraging for food, many creatures follow a particular and shared pattern. They walk (or wing or lope) for a short time in one direction, scouring the ground for edibles, then turn and start moving in another direction for a short while, before turning and strolling or flying in another direction yet again. This is a useful strategy for finding tubers and such, but if maintained indefinitely brings creatures back to the same starting point over and over; they essentially move in circles. Copyright 2014 The New York Times Company
By CARL ZIMMER There are many things that make humans a unique species, but a couple stand out. One is our mind, the other our brain. The human mind can carry out cognitive tasks that other animals cannot, like using language, envisioning the distant future and inferring what other people are thinking. The human brain is exceptional, too. At three pounds, it is gigantic relative to our body size. Our closest living relatives, chimpanzees, have brains that are only a third as big. Scientists have long suspected that our big brain and powerful mind are intimately connected. Starting about three million years ago, fossils of our ancient relatives record a huge increase in brain size. Once that cranial growth was underway, our forerunners started leaving behind signs of increasingly sophisticated minds, like stone tools and cave paintings. But scientists have long struggled to understand how a simple increase in size could lead to the evolution of those faculties. Now, two Harvard neuroscientists, Randy L. Buckner and Fenna M. Krienen, have offered a powerful yet simple explanation. In our smaller-brained ancestors, the researchers argue, neurons were tightly tethered in a relatively simple pattern of connections. When our ancestors’ brains expanded, those tethers ripped apart, enabling our neurons to form new circuits. Dr. Buckner and Dr. Krienen call their idea the tether hypothesis, and present it in a paper in the December issue of the journal Trends in Cognitive Sciences. “I think it presents some pretty exciting ideas,” said Chet C. Sherwood, an expert on human brain evolution at George Washington University who was not involved in the research. Dr. Buckner and Dr. Krienen developed their hypothesis after making detailed maps of the connections in the human brain using f.M.R.I. scanners. When they compared their maps with those of other species’ brains, they saw some striking differences. © 2013 The New York Times Company
By Melissa Hogenboom Science reporter, BBC News An analysis of a Neanderthal's fossilised hyoid bone - a horseshoe-shaped structure in the neck - suggests the species had the ability to speak. This has been suspected since the 1989 discovery of a Neanderthal hyoid that looks just like a modern human's. But now computer modelling of how it works has shown this bone was also used in a very similar way. Writing in journal Plos One, scientists say its study is "highly suggestive" of complex speech in Neanderthals. The hyoid bone is crucial for speaking as it supports the root of the tongue. In non-human primates, it is not placed in the right position to vocalise like humans. An international team of researchers analysed a fossil Neanderthal throat bone using 3D x-ray imaging and mechanical modelling. This model allowed the group to see how the hyoid behaved in relation to the other surrounding bones. Stephen Wroe, from the University of New England, Armidale, NSW, Australia, said: "We would argue that this is a very significant step forward. It shows that the Kebara 2 hyoid doesn't just look like those of modern humans - it was used in a very similar way." He told BBC News that it not only changed our understanding of Neanderthals, but also of ourselves. "Many would argue that our capacity for speech and language is among the most fundamental of characteristics that make us human. If Neanderthals also had language then they were truly human, too." BBC © 2013
By JOHN NOBLE WILFORD Early in the 20th century, two brothers discovered a nearly complete Neanderthal skeleton in a pit inside a cave at La Chapelle-aux-Saints, in southwestern France. The discovery raised the possibility that these evolutionary relatives of ours intentionally buried their dead — at least 50,000 years ago, before the arrival of anatomically modern humans in Europe. These and at least 40 subsequent discoveries, a few as far from Europe as Israel and Iraq, appeared to suggest that Neanderthals, long thought of as brutish cave dwellers, actually had complex funeral practices. Yet a significant number of researchers have since objected that the burials were misinterpreted, and might not represent any advance in cognitive and symbolic behavior. Now an international team of scientists is reporting that a 13-year re-examination of the burials at La Chapelle-aux-Saints supports the earlier claims that the burials were intentional. The researchers — archaeologists, geologists and paleoanthropologists — not only studied the skeleton from the original excavations, but found more Neanderthal remains, from two children and an adult. They also studied the bones of other animals in the cave, mainly bison and reindeer, and the geology of the burial pits. The findings, in this week’s issue of Proceedings of the National Academy of Sciences, “buttress claims for complex symbolic behavior among Western European Neanderthals,” the scientists reported. William Rendu, the paper’s lead author and a researcher at the Center for International Research in the Humanities and Social Sciences in New York, said in an interview that the geology of the burial pits “cannot be explained by natural events” and that “there is no sign of weathering and scavenging by animals,” which means the bodies were covered soon after death. © 2013 The New York Times Company
Link ID: 19041 - Posted: 12.17.2013
By CARL ZIMMER Scientists have found the oldest DNA evidence yet of humans’ biological history. But instead of neatly clarifying human evolution, the finding is adding new mysteries. In a paper in the journal Nature, scientists reported Wednesday that they had retrieved ancient human DNA from a fossil dating back about 400,000 years, shattering the previous record of 100,000 years. The fossil, a thigh bone found in Spain, had previously seemed to many experts to belong to a forerunner of Neanderthals. But its DNA tells a very different story. It most closely resembles DNA from an enigmatic lineage of humans known as Denisovans. Until now, Denisovans were known only from DNA retrieved from 80,000-year-old remains in Siberia, 4,000 miles east of where the new DNA was found. The mismatch between the anatomical and genetic evidence surprised the scientists, who are now rethinking human evolution over the past few hundred thousand years. It is possible, for example, that there are many extinct human populations that scientists have yet to discover. They might have interbred, swapping DNA. Scientists hope that further studies of extremely ancient human DNA will clarify the mystery. “Right now, we’ve basically generated a big question mark,” said Matthias Meyer, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and a co-author of the new study. Hints at new hidden complexities in the human story came from a 400,000-year-old femur found in a cave in Spain called Sima de los Huesos (“the pit of bones” in Spanish). The scientific team used new methods to extract the ancient DNA from the fossil. “This would not have been possible even a year ago,” said Juan Luis Arsuaga, a paleoanthropologist at Universidad Complutense de Madrid and a co-author of the paper. © 2013 The New York Times Company
Barn owl nestlings recognise their siblings' calls, according to researchers. Instead of competing aggressively for food, young barn owls are known to negotiate by calling out. A team of scientists in Switzerland discovered that the owlets have remarkably individual calls. They suggest this is to communicate each birds' needs and identity in the nest. The findings were announced in the Journal of Evolutionary Biology by Dr Amelie Dreiss and colleagues at the University of Lausanne, Switzerland. Barn owls (Tyto alba) are considered one of the most widespread species of bird and are found on every continent except Antarctica. An average clutch size ranges between four and six eggs but some have been known to contain up to 12. Previous studies have highlighted how barn owl nestlings, known as owlets, negotiate with their siblings for food instead of fighting. While their parents search for food the owlets advertise their hunger to their brothers and sisters by calling out. "These vocal signals deter siblings from vocalizing and from competing for the prey at parental return," explained Dr Dreiss. "If there is a disagreement, they can escalate signal intensity little by little, always without physical aggression, until less hungry siblings finally withdraw from the contest." BBC © 2013