Blogs / 80beats

Great white sharks, much like humans, tend to stick to familiar turf, according to new research. Also like a lot of people, they like to hang out along the coastal waters of California. Sharks tagged with acoustic devices often spent up to 107 days at four key sites along the central and northern California coast where seals and sea lions are abundant: Southeast Farallon Island, Tomales Point, Año Nuevo Island and Point Reyes [LiveScience]. A few of the fearsome predators were tracked as far inland as the Golden Gate Bridge, apparently in search of snacks, say the researchers. The study, the largest and most detailed study of North American great white sharks, provides evidence contrary to the popular notion of great white sharks swimming aimlessly in the ocean.

The sharks under study divided most of their time between three locations: Northern California, Hawaii, and an area that the researchers called the white shark café, a spot in the open ocean about halfway between the Baja Peninsula and the Hawaiian Islands. Exactly what goes on at the café is still unknown–although researchers suspect it may be a hot spot for mating. Lead researcher Salvador Jorgensen explains that male white sharks “converge in a very specific area of the cafe,” Jorgensen said, while female sharks move in and out of the area. “It adds a little more evidence to the argument that this could be an important reproductive area” [Washington Post].

The scientists tracked the snaggly toothed predators between 2000 and 2008 from the Bay Area to San Diego, Hawaii and back as the sharks followed a route that was carried out with surprising precision and under a strict time frame [San Francisco Chronicle]. These great whites have been isolated from other great white sharks near Australia and South Africa for so long that they are now genetically distinct. The study was published in the journal Proceedings of the Royal Society B.

Related Content:
80beats: Toothy Sea Monsters Need Sanctuary, To
80beats: The Great White Shark Is the Serial Killer of the Seas
80beats: Human Appetite for Sharks Pushes Many Toward Extinction

Image: flickr / hermanusbackpackers

According to legend, the infamous Tsavo man-eating lions dined on 135 people near a Kenyan labor camp prior to their capture in 1898. The two maneless lions have been a crowd favorite at Chicago’s Field Museum, where the stuffed beasts have been on display for over 80 years. But after analyzing fragments of the lions’ bones and fur, scientists at the University of California in Santa Cruz have determined that the true number of humans eaten by the lions was likely closer to 35. By comparing isotopes in the lions’ samples with their normal prey of zebra, wildebeest and buffalo, with other lions, and with the remains of 19th century Kenyans, the scientists estimated that one of the lions ate 24 humans, while the other ate 11 [Chicago Tribune]. The results suggest that the lions hunted together but didn’t always share food, which makes the pair the first example of a cooperative hunting group that ate different prey.

The two lions developed a taste for man after drought, pestilence, and hunting killed of most of their usual prey, according to previous research. Also, the Tsavo lions lived near a slave trading route, which offered easy access to sick, injured, or dead slaves. The lions dragged people from tents at night…. After nine months of this, the beasts were finally killed in December [Nature News]. The recent analysis suggests one of the lions had developed a toothache, which made eating humans easier than devouring its normal prey. The study attributes 24 deaths to one cat, or 30 per cent of its diet, and 11 deaths to the other, just 13 per cent of its food [New Scientist].

Colonel John H. Patterson, a British engineer, shot the lions and then wrote a book about their killing spree, claiming that “28 railroad workers and scores of unfortunate Africans” had been killed [Chicago Tribune]. Some believe that in order to boost the selling price of the lions, he exaggerated the lions’ man-killing ways and inflated the death count to 135.  Patterson sold the lion skins for $5,000 to the Field Museum in 1924.

The current study appears in the journal Proceedings of the National Academy of Sciences.

Related Content:
80beats: Tigers and Humans Tangle in Sumatra; Both Sides Lose
80beats: Lion Die-Off Shows How Climate Change Can Cause Epidemics

Image: flickr / lisa andres

Before one species of jumping spider, known as Evarcha culicivora, goes trolling for a mate, it firsts look to feast on blood-fattened mosquitoes. What happens next seems like something out of a bad video game: The delicacy gives the spider a special power–a sweet smell that the opposite sex finds irresistible.

In a new study, which will be published in the Proceedings of the National Academy of Sciences, researchers exposed E. culicivora specimens to the odors of others raised on blood-fed female mosquitoes and on three other diets: sugar-fed females, males and lake flies…. [The] tested spiders of both sexes were most strongly attracted to the odor of spiders reared on blood-fed female mosquitoes. But the attraction was only for spiders of the opposite sex [The New York Times].  Spiders would hang around blood-fattened spiders of the opposite sex four times longer than they would linger around those fed on another diet. The blood perfume effect might only be triggered by a gender specific hormone, the researchers suggest.

(more…)

A jumping spider that passes on eating ants in favor of leafy greens has just been described by scientists. The novel arachnid, named Bagheera kiplingi, is exciting because it is the first-known predominantly vegetarian spider; all of the other known 40,000 spider species are thought to be mainly carnivorous [BBC News]. The study was published in the journal Current Biology.

Found in Central America and Mexico, the order-defying jumping spider eats nutrient-rich structures called Beltian bodies, which are found on the tips of Acacia trees. Trees produce the bodies to feed ants that defend them, which is a textbook example of what’s called co-evolutionary mutalism, and one that B. kiplingi has evolved to exploit [Wired.com]. Despite a primarily veggie diet, B. kiplingi actively hunts its green prey, which sounds bizarre, since the leaves can’t run away. The spider first sits and stalks its target before it dodges through the ant defenses, snatches a Beltian body, and flees to safety.

(more…)

Following up on today’s earlier post about alcohol and brain injuries, we bring you a study on alcohol and risk taking behavior. It seems obvious that drinking alcohol would lead to immediate risk taking, but does drinking as a teenager lead to risk taking behavior as an adult? Some researchers have suspected as much, but they haven’t been able to rule out the possibility that risk-prone people simply start drinking at an earlier age. So a research group chose an obvious course of action to test the idea—they got a bunch of rats drunk and let them gamble.

The researchers tested two groups of genetically identical rats, one group that was fed a normal diet and another that boozed it up. To get the rats drunk, the researchers borrowed the tried-and-true approach of frat boys everywhere—they fed them Jell-O shots. The rats went on a 20 day bender and were tested for risky behavior 3 weeks later, when they were adults, using a gambling task. The animals learned that pressing one lever produced small but certain rewards in the form of small sugar pellets and an adjacent lever yielded bigger rewards—more pellets—but paid off less frequently. The researchers rigged the game so that in some testing sessions choosing the certain reward was the best overall strategy, while in other sessions the “risky” lever yielded the greatest overall payoff [ScienceNOW Daily News].

(more…)

When a gecko is desperately trying to escape from a predator, it has a creepy trick: It detaches its tail and leaves it wriggling on the ground to distract the hunter, while the rest of the lizard scampers off. Now, with high-speed video researchers have studied what happens to the left-behind tail, and they found that it flips and flops acrobatically, and changes direction and speed depending on what it bumps into. Researchers (and lizard-watching kids) already knew that the severed tail continues to move, but this study in the journal Biology Letters is the first to determine that the tail can independently respond to its environment.

Says lead researcher Anthony Russell: “The tail is buying the animal that shed it some time to get away.” … If the tail simply moved rhythmically back and forth, predators would quickly recognize a pattern and realize they’d been duped. Unpredictable tail movements keep predators occupied longer, and in some cases, they may even allow the tail itself to escape [Wired.com]. Russell notes that the leopard geckos he studied store fat in their tails, and suggests that if the tail can flop far enough away from the predator the gecko could return later to eat its own tail.

(more…)

Yawning is so contagious that even chimpanzees who watched animations of cartoon chimps yawning couldn’t resist the impulse, according to a new study in Proceedings of the Royal Society B. Study coauthor Matthew Campbell doesn’t think the chimps were “fooled” by the animations into thinking they were looking at real chimps, he explained that there was evidence that chimpanzees “process animated faces the same way they process photographs of faces”. He said: “It’s not a real chimpanzee, but it kind of looks like a chimpanzee, and they’re responding to that” [BBC News].

The chimps were tested by first showing them animated chimps making a variety of facial expressions, and then another set of cartoons with yawning chimps. Only the latter cartoons elicited the yawning response. Campbell says the findings could assist in the future study of empathy…. “We’re interested in using animation for presenting stimuli to animals, because we can control all the features of what we show them” [BBC News].

As for why yawns are so contagious, Campbell suggests that the phenomenon may have evolved to allow some animals “to coordinate activity better, resting when other individuals are resting” in order that they “can travel when it’s time to travel, eat when it’s time to eat” [Discovery News].

Related Content:
80beats: Scientists Tickle Apes & Conclude Laughter Is at Least 10 Million Years Old
80beats: Male Chimpanzees Share Meat in Return for Sex
80beats: Chimp Gathers Stones for “Premeditated” Attacks on Zoo Visitors

Image: J. Devyn Carter. Still frames from the animated yawning. 

Imitation may be the sincerest form of flattery not just for humans, but for many primates. In human social interactions, people have an instinctive tendency to copy each other’s body language and mannerisms, and previous studies have shown that such imitation gives rise to friendly feelings. Now a new study has found that capuchin monkeys respond to imitation in the same way, suggesting that the behavior may date back to early in our evolutionary history. The subtle aping may promote the formation of social groups—building cooperation, reducing conflict, and aiding the survival of each individual [Scientific American].

To study the behavior in capuchin monkeys, which live in highly social groups of 30 or 40 individuals, the researchers gave each monkey a Wiffle ball — a lightweight plastic ball with holes in it. Monkeys typically poked the ball with their fingers, put it in their mouths or used it to pound on something. Each monkey was paired up with two human researchers, one that copied their ball-handling skills, and one that did not. When the balls were put away, the monkeys appeared to prefer the company of the like-minded ball handler [Reuters].

(more…)

Scientists have discovered a clever way the yellow-lipped sea krait snakes deter predators: By making it look as though the venomous snake has two heads, according to a study published in the journal Marine Ecology.

A biologist first noticed the snakes’ tricky method while diving in Indonesia. Researcher Arne Rasmussen observed the animals foraging for food while simultaneously moving what appeared to be a bobbing head around–but that bobbing body part was really its tail. “[T]he tail was slowly writhing back and forth, much in the same way as the head moves on a vigilant and actively searching snake” [National Geographic News], said co-author Johan Elmberg, who did not see the snake, but teamed up for the study with Rasmussen.

(more…)

A quartet of clever rooks have provided evidence that one of Aesop’s fables could have a basis in fact. The tale in question tells the story of a thirsty crow. The bird comes across a pitcher with the water level too low for him to reach. The crow raises the water level by dropping stones into the pitcher. (Moral: Little by little does the trick, or in other retellings, necessity is the mother of invention) [AP]. In the new lab experiment, four rooks each dropped stones into a clear plastic tube, which raised the water level high enough to bring a floating worm within reach.
Rooks and crows are both in the corvid family, which researchers say rivals the great ape family for intelligence and tool use–the only other animal that has performed a comparable task was an orangutan, who spat into a tube to gain a floating peanut. Says study coauthor Nathan Emery: “We have performed a large number of studies on both corvids … and apes, and have found that the crow’s performance is on a par or often superior to apes. However, it is not particularly useful to say that one species is more or less intelligent than another because often the playing fields aren’t even” [The Independent]. 

(more…)

Plenty of cat owners joke about being at the beck and call of a demanding feline, and now researchers have identified one vocal tactic that house cats use to manipulate their owners. The newly identified vocalization, called “solicitation purring,” has never been acknowledged or studied before, although cat fanciers, such as the study’s lead author Karen McComb, are quite familiar with it. “In the case of my cat, if he sees you stirring from sleep at all in the early morning he will immediately switch into giving this solicitation purring and position himself next to your head so you get the full impact” [Discovery News], she says.

Unlike the low-pitched purr that cats produce when they’re lazily lounging, this sound incorporates a high-pitched “cry” with a similar frequency to a human baby’s. The team said cats have “tapped into” a human bias – producing a sound that humans find very difficult to ignore [BBC News]. McComb suggests that cats may learn to embed the subtle wake-up call within the purring sound usually associated with contentment because more overt meowing is likely to get them kicked out of bed.

(more…)

To get inside the head of a homing pigeon as it navigates towards its roost, researchers turned a flock of pigeons into cutting-edge techno-birds. The scientists outfitted the birds with “neurologgers” consisting of an electroencephalograph (EEG) to read the bird’s brain waves and a GPS tracker to record its location; by matching a bird’s position to its brain activity, the researchers could determine the bird’s reaction to the landscape below it. They found that, just like humans, the pigeons use visual landmarks in their navigation.

How homing pigeons find their way back to a starting point is not completely known. Studies have shown that the birds variously use the position of the Sun and the Earth’s magnetic field as a compass, and sense of smell and visual cues as navigation aids. But the use of visual cues has been difficult to study, because if a bird flies over a landmark and doesn’t change its course, it’s impossible to know whether the bird has not perceived the cue or is ignoring it [The New York Times].

(more…)

A tiny fish common in European streams may learn in a more sophisticated way than has ever been recorded among animals and which mimics human learning. In a study published in the journal Behavioral Ecology, scientists found that the nine-spined stickleback fish used the success and failures of their peers to gauge where they should seek food.

The fish were shown to display a type of learning known as “hill-climbing,” in which an entity continually looks for a better solution to a problem; in this case, one fish copied others that were more successful in finding food. Researchers caught 270 nine-spined sticklebacks in Leicester, England. The fish were organized into experimental groups. These fish groups then took turns as either free swimmers in a tank with worm-yielding feeders at the end, or as “learners” in a transparent, partitioned-off area of the specially designed tank. One of the two feeders released more worms than the other [Discovery News].

The first group of free-swimming fish quickly learned which feeder was full of worms, and were then put into the observers’ chamber. Next, researchers switched which feeder held the worms, and the fish in the observation tank watched the next fish group identify the new worm-filled feeder. After switching the two groups of fish again, the original group made a beeline for the feeder full of worms that their peers had fed from.

(more…)

It’s hard to imagine having more fun in the name of science: In a new study, researchers tickled young chimpanzees, bonobos, gorillas, orangutans, and even a few human babies, and recorded the vocalizations that resulted. Primatologist Marina Davila Ross wanted to examine the evolutionary history of laughter, so she and her colleagues recorded the sounds produced when they tickled 22 great apes and 3 human babies, picking the usual sensitive spots: armpits, palms, feet, and necks.

Scientists have known that great apes vocalize when tickled at least since Charles Darwin’s time. But it was unclear whether these sounds were actually related to human laughter. Now, researchers … have concluded that laughter has been evolving in primates over the last 10 to 16 million years, since at least the last common ancestor of humans and modern great apes [Wired.com].

(more…)

When a banana is at stake, a low-status capuchin monkey may deceive the other monkeys in his troupe in order to get his hands on that tasty fruit. A new study of monkeys in an Argentinian national park found evidence that lowly monkeys give spurious alarm calls in order to scare off more dominant monkeys competing for food.

Tufted capuchin monkeys give a two-syllable “hiccup” call when they detect danger, like an approaching ocelot. Lead researcher Brandon Wheeler was studying a group of capuchins eating food left on platforms constructed in trees, when he noticed some of the monkeys made the calls when predators weren’t around. “They were giving the same calls that they give for cats extremely frequently,” he says. “When they do, other individuals often run out off the platform, which potentially leaves [the platform] available for whoever called to jump in to get some food” [ScienceNOW Daily News].

(more…)