It found adult wild long-tailed macaque monkeys were intelligent enough to comprehend which items had the highest value to the visitors, such as an electronic item, and would only release it after receiving food they perceived to be of corresponding value.
The authors said the behavior displayed "unprecedented economic decision-making processes" among the monkeys observed as part of the study.
An understanding of economics
The scientists, from the University of Lethbridge, Canada, and Udayana University, Indonesia, observed that, as well as being able to "use objects as symbolic tools to request specific food rewards," the ability of the monkeys to barter successfully increased with age and experience.
There were "clear behavioral associations between value-based token possession and quantity or quality of food rewards rejected and accepted by subadult and adult monkeys," the authors said, with older monkeys "preferentially" selecting higher value items.
The research, published Monday, was conducted over 273 days from 2015 to 2016, with further observations conducted in 2019.
The scientists filmed the monkeys as they stared at a visitor, inconspicuously approached them, took an object, and then stepped aside waiting for a suitable offering.
The adult monkeys accumulated "several food rewards before returning the token" where the item was of high value, and were "more likely" to accept a "less preferred food reward" in exchange for a lower value item, the study said.
"Token-robbing and token/reward-bartering are cognitively challenging tasks for the Uluwatu macaques that revealed unprecedented economic decision-making processes," the authors said.
"This spontaneous, population-specific, prevalent, cross-generational, learned and socially influenced practice may be the first example of a culturally maintained token economy in free-ranging animals."
6-foot megalodon shark babies were cannibals in the womb, study says
These extinct sharks gave birth to some really large babies -- about the size of a full-grown human adult.
At birth, megalodons were about 6.6 feet, or 2 meters, in length, according to a study published Sunday in the Historical Biology journal.
Megalodons, scientifically known as Otodus megalodon, were huge sharks that grew up to 50 feet in length and roamed the oceans 15 million to 3.6 million years ago, said study author Kenshu Shimada, professor of paleobiology at DePaul University in Chicago.
The 6.6-foot measurement is fairly accurate and aligns with other findings at megalodon nurseries in Panama and Spain, said Jack Cooper, a fossil shark researcher and doctoral student at Swansea University's department of biosciences in Wales, United Kingdom, who was not involved in the study.
The study is significant because there is not much research out there about the megalodon's reproduction, he said.
To find the animal's length at birth, researchers looked at CT scans of a megalodon's vertebrae that was originally found in Belgium in the 1860s. Much like the rings of a tree, a megalodon's vertebrae have annual growth bands that allow scientists to track the shark's age.
The specimen was believed to be 46 years old when it died, so Shimada counted the growth bands back to the birth ring and calculated the length of the animal at birth. This particular shark was estimated to be about 30 feet in length at death.
Survival of the fittest
These extinct sea creatures didn't grow that large in the womb by luck.
While growing inside its mother, megalodons would eat other unhatched eggs, which is known as intrauterine cannibalism.
"The consequence of the egg-eating behavior is that only a few pups will survive and develop, but each of them can become considerably large in size at birth," Shimada said.
Their large size at birth reduces the chances of the baby megalodons from being eaten by other predators.
Some modern-day sharks that are a part of the order Lamniformes -- the same one the megalodons belong to -- also practice this behavior.
Sand tiger sharks eat other unhatched eggs in the womb, and Shimada said that they sometimes also eat other hatched siblings.
It costs female sand tiger sharks a lot of energy to raise such large babies, he says, but similar to the megalodon, this evolutionary strategy reduces the chances of them being eaten after birth.
Much is still unknown about the giant shark, said Shimada, who wants to discover more. He has had an interest in the megalodon since he was 13 years old when he found a 2-inch megalodon tooth at a geology site outside Tokyo.
While this study has revealed much about the birth of a megalodon, the specimen was only 46 years old, which is middle age for this animal.
Shimada hopes to research the shark's later years, which is estimated to be between 88 to 100 years old, to learn its growth pattern.
This snake turns its body into a lasso to climb up smooth surfaces
Scientists have discovered that brown tree snakes can use a lasso-like movement to climb large, smooth cylindrical objects -- a way of moving never seen before in the reptiles.
Experts from Colorado State University and the University of Cincinnati made the discovery by chance while working on a project aimed at protecting the nests of Micronesian starlings on Guam -- one of only two native species remaining on the island.
People accidentally introduced brown tree snakes to the Western Pacific territory in the 1940s-50s, and the invasive species has since decimated forest bird populations on the island, as well as being responsible for power outages.
Using a three-foot metal baffle -- often used to keep birds safe from racoons and other snakes -- researchers attempted to keep the tree snakes from climbing up to bird boxes.
But, to their astonishment, video surveillance of the boxes revealed a brown snake writhing its way up to the bird box, having formed a lasso around the cylindrical pole, eight inches in diameter, with its body.
Snakes generally use one of four types of locomotion -- known as rectilinear, lateral undulation, sidewinding and concertina modes -- in order to move. When climbing steep and smooth surfaces, like branches or pipes, the animals typically use a "concertina" movement, bending sideways to grip in at least two places.
But by "lassoing," the snakes are able to form a single gripping region, with little bends formed in the loop of the lasso, allowing them to advance slowly upward, researchers said.
"We didn't expect that the brown tree snake would be able to find a way around the baffle," study co-author Thomas Seibert, of Colorado State University, said.
"Initially, the baffle did work, for the most part," Seibert said. But after four hours of video footage, "all of a sudden, we saw this snake form what looked like a lasso around the cylinder and wiggle its body up. We watched that part of the video about 15 times. It was a shocker. Nothing I'd ever seen compares to it," he said.
Researchers say this way of moving isn't necessarily easy for the snakes, which often slipped, moved slowly, breathed heavily and stopped to rest.
"Even though they can climb using this mode, it is pushing them to the limits," said co-senior author Bruce Jayne of the University of Cincinnati.
But however difficult, researchers say the movement allows the reptiles to attack unsuspecting prey, and could explain how they are able to climb power poles, which leads to electrical outages.
"Understanding what brown tree snakes can and cannot climb has direct implications for designing barriers to reduce the dispersal and some of the deleterious effects of this highly invasive species," Jayne said.
The researchers say they want to use their new knowledge of how the snakes move to better protect birds in the area.
"Given that brown tree snakes can use lasso locomotion to defeat poles or cylinders of a certain size," Seibert said, "we can design baffles to better protect bird houses used for restoring some of Guam's birds."
Russian woman who swam under Siberia's ice may have broken the world record
Wearing nothing but a bathing suit, a swimming cap and an underwater mask, the 40-year-old woman plunged into a carved-out section of a frozen Siberian lake, before diving under the ice to swim in water estimated to be around 32 degrees Fahrenheit.
Footage tweeted by the English language Siberian Times shows the 40-year-old woman from Moscow entering the carved-out section of a frozen Lake Baikal, before she started the underwater ice swim.
Yekaterina Nekrasova, who took up free diving four years ago, then held her breath for a minute and a half as she covered the 85 meters (279 feet) of a frozen Lake Baikal on January 7 -- the Russian Orthodox Christmas Day.
She is believed to have set a world record with her attempt. A spokeswoman for Guinness World Records told CNN they have received details of Nekrasova's attempt but have yet to verify the landmark swim.
Footage filmed from above the surface shows members of her support team following behind in wet suits, in case of emergency. According to the Siberian Times, holes were cut in the 10-inch-thick ice at regular intervals in case she needed to abort the swim.
The challenge was filmed from both above and beneath the surface. Nekrasova can be seen descending a ladder, then following a route marked by a cable for a minute and a half. At the end she exits the water by climbing up another ladder.
Met by her support team, Nekrasova emerges to say in English: "I'm OK."
Lake Baikal holds several global records itself. Somewhere between 20 and 25 million years old, it is the oldest existing freshwater lake on Earth. Reaching down as far as 5,315 feet, it is the deepest continental body of water, as well as being the world's largest freshwater lake by volume -- it holds about one-fifth of the fresh water on Earth's surface, some 5,500 cubic miles.
Posting on Russian social network site VK, Nekrasova said the original plan was to swim on January 6 but "extreme weather" -- including a "very strong frost" and stormy winds -- delayed it.
While she knew that she could "comfortably" swim 75 meters (246 feet), Nekrasova said doubts began to creep in.
"I thought what if I would freeze before the start, or the mask would freeze or fog up, or I would stick to the ice at the finish line. And of course I didn't know how long I could dive in a new place," she wrote.
The air temperature was as low as -22 degrees Fahrenheit but felt more like -43.6 on January 6, she said. Conditions were "dangerous and dark under the ice," which convinced the team to postpone the attempt.
Nekrasova described what happened the following day as a "Christmas miracle."
"The weather warmed up to -21 (degrees Celsius, -5.8 Fahrenheit ), the wind slightly moderated," she wrote. As her support team prepared the site with safety lanes and holes in the ice, she remained at her hotel.
Having warmed up, she made her way to the starting point, where she was joined by her support team.
"For a minute I stood dressed in front of the ladder, tuned in, breathing, the wind was strong. I put on a mask, undressed and hurried into the water. There is no wind, no frost, no fear in the water and it is very comfortable. I stood for about 30 seconds until the pulse calmed down. Then I dived."
Describing the experience as a "pleasure," said she "enjoyed the process" and that ultimately she was "overwhelmed with emotions."
Signing off, she added: "The powerful energy of this place helped me. Thank you Baikal! Until next time!"
Ice swimming, or epiphany bathing, is a tradition in Russia. For many Orthodox Christians, it is part of a January ritual commemorating the baptism of Jesus.
Nekrasova, who trains four times a week in a warm pool and dives twice in a week in ice holes in Moscow, told CNN: "For me, under-ice diving is like an energy boost, as if I was reborn. It is a sensation I can't compare to anything else, a very pleasant one. And I always long for it."
Ram Barkai, the founder of the International Ice Swimming Association, told CNN he and a team of four Russian ice swimmers covered an above-surface "ice mile" in Lake Baikal at 40.1 degrees Fahrenheit back in 2017.
By comparison, Nekrasova is a free diver -- which means she held her breath for the duration of the swim at close to 32 degrees Fahrenheit, under a sheet of ice.
He said: "The water there is as fresh as one can get -- salinity of zero. Meaning you are heavier in the water and you feel the cold a little more than in salt water.
"It is a magical place, Lake Baikal. The water visibility is also amazing, crystal clear water and you can see forever. That is a good factor for safety."
Of Nekrasova's achievement, he said: "The water should have been close to zero, which makes it extremely hard on your muscles. She swam without any assistance -- gliding very efficiently. It was amazing to watch her.
"Eighty-five meters is a very long distance in warm water with no ice sheet above your head. Although she had a line to show her direction and distance, she wasn't attached to anything, with few ice holes on the way. Typical hardcore Russian style."
According to Guinness World Records, the record for the longest swim under ice is held by Dane Stig Severinsen, who swam 250 feet in Greenland in 2013.
The record for the longest female swim under ice is 229.659 feet and was achieved by South African Amber Fillary in Oppsjø, Norway, on February 29, 2020.