April 11, 2013
Visitors to Guam’s forests find them quiet–eerily so: No chirping of birds can be heard overhead. But slithering in the shadows on the ground are snakes, each some six feet long. Brown tree snakes made their debut on Guam, the southernmost island in the Mariana Archipelago, when islanders were rebuilding after World War II. Most likely, they were stowaways in lumber shipments heading north through the Pacific Ocean from New Guinea. They quickly began feasting on the birds and small lizards they discovered in Guam’s dense forests, and–free to slither through the mountainous terrain without predators of their own–they completed an invasion of the island at a pace of one mile per year. By the late 1940s, the forests had largely fallen silent, and now, all of Guam’s native bird species are history.
Last fall, scientists from Rice University and the University of Guam published one of the first studies of the island’s extinct forest birds, which include species such as the Mariana fruit dove, Guam flycatcher and Rufous fantail. They focused on how the absence of birds has caused a spike in the spider population, which is 40 times greater on Guam than nearby islands.
Now, the researchers are turning their attention to the issue of Guam’s thinning forests—a consequence, they also believe, of the bird deficit. This summer they’ll launch a four-year study of 16 tree species, looking at how the loss of birds, which scatter seeds, is affecting tree distribution.
The study has its roots in an a-ha moment that lead scientist Haldre Rogers recently had while conducting another seed-dispersal study in Guam’s forests. “I noticed that there seemed to be a lot of gaps [in the trees] and that the pioneer tree species–such as papaya and sumak–were difficult to find on Guam, compared to nearby islands,” she explained to Surprising Science. She discovered that there were in fact twice as many such gaps on Guam per unit area of forest.
Pioneer trees, which are the first to appear after a disruption to the ecosystem and thrive in the full sunlight of open spaces in the forest, have small seeds that are consumed by small birds. “Without birds to move their seeds to these sunny spots in the forest, these quick-growing trees may be less likely to germinate or grow to their full size,” Rogers hypothesized.
The problem with such thinning is that it could change the structure of Guam’s forests. “There’s a concern that [they] may become filled with open areas and start to look more like Swiss cheese than a closed canopy forest,” Rogers said. In other words, what were once cool, dark forests could transform into hot, open sunny ones.
There are other possible explanations for the tree-thinning: An undiscovered forest disease could be targeting pioneer species, or mammals like pigs and deer might have a strong taste for the trees. But according to Rogers, there isn’t strong evidence to support either of these scenarios. The upcoming study will attempt to determine the cause definitively.
To that end, the researchers will cut down individual trees in various spots within Guam’s forests, creating new gaps in the forest. They’ll also remove trees from locations on two nearby islands that are still brimming with birds. Then they’ll monitor how long it takes the spaces to fill in and take note of which seedlings thrive on Guam versus on the other islands. It may seem that to get their results they’re destroying what they’re trying to study, but in actuality they’re taking down a tiny percentage of the island’s trees–20 total.
Guam’s situation is similar to that of tropical regions worldwide. “Animals involved in seed-dispersal are in decline in a lot of tropical forests around the world right now,” the co-principal investigator of the study, Amy Dunham, said in a statement. “It’s very important to understand the implications of those declines.” So far scientists have looked into the role of endangered mammals like lemurs, giant tortoises (PDF) and African forest elephants (PDF) in seed dispersal, but the upcoming study will be one of the first to focus on endangered birds.
It’s also the rare study to examine what happens when seed dispersal completely ceases–Guam being the only place in the world to experience whole-island forest bird loss in modern times. “The situation on Guam–which is tragic–provides us with a unique opportunity to see what happens when all seed-dispersal services provided by animals are lost from an entire ecosystem,” Dunham said.
The snakes, meanwhile, continue to dominate the island of Guam. The U.S. Department of Agriculture traps approximately 6,000 brown tree snakes each year, and yet there are still nearly two million slithering around the island. The snakiest patches contain 14,000 of the reptiles per square mile–one of the highest snake concentrations in the world.
In February, the Department of Agriculture embarked on a new tactic for tackling the snake problem: dropping dead mice laced with acetaminophen, which is fatal to them, into the jungle. ”We are taking this to a new phase,” Daniel Vice of the Department of Agriculture’s branch that focuses on wildlife services in Hawaii, Guam and other U.S. held Pacific Islands, said in a recent interview. “There really is no other place in the world with a snake problem like Guam.”
April 1, 2013
Anyone who lives in or has visited a tropical country is likely familiar with the chipper chirping of the gecko. These friendly little lizards inhabit homes and jungles stretching from Indonesia to Tanzania to the Dominican Republic. They emerge after sunset, taking advantage of their night vision eyesight—which is 350 times more powerful than a human’s—and are welcome guests in homes and hotels since they gobble up mosquitoes and other insect pests.
In addition to the locals, scientists also love these colorful lizards. Geckos possess the unique ability among lizards to run up flat walls and scamper across ceilings, even if the surface is very smooth. Researchers have been puzzling over this ability for years, and dozens of labs have tested gecko adhesion in the hopes of harnessing this superpower for potential use in everything from robotics to space technology to medicine to “gecko tape.”
Gecko toes, it turns out, contain hair-like structures that form a multicontact interface, meaning geckos grip with thousands of tiny adhesive structures rather than what appears to be a single uniform foot.
Gaps remain, however, in researchers’ understanding of how gecko feet interact with surfaces in their natural environment, especially in dry versus wet conditions. Scientists know that gecko toe pads are superhydrophobic, or water repelling, yet geckos lose their ability to cling to glass when it becomes wet. Why don’t they just repel the water and cling to the glass surface below? Similarly, scientists wonder how geckos deal with wet leaves in the forest during rain storms.
A new paper published in Proceedings of the National Academy of Sciences investigates these mysteries. The authors decided to test gecko grip on a range of wet and dry materials that both attract and repel water. To perform their experiments, they outfitted six tokay geckos with gecko-sized harnesses. They placed the geckos onto four different types of materials, such as glass, plastic and a substance designed to mimic waxy tropical leaves. After giving the lizards some time to adjust to their new surroundings, the researchers applied a uniform tugging pressure onto the geckos’ harnesses, pulling in the opposite direction of where the animals were walking. Eventually, the geckos could cling no longer and lost their grip. This allowed the team to measure the adhesive force required to displace the animals. They repeated the same experiments under very wet conditions, too.
The authors found that materials that are more “wettable”—an indication of the degree to which a surface attracts water molecules—the less force it took to disrupt the clinging geckos’ grips. Glass had the highest wettability of the surfaces the researchers tested, and geckos easily slipped from wet glass compared to dry glass. When that material gets wet, water forms a thin, attractive film that prevents the gecko’s tiny toe hairs from coming into contact with the surface.
The low wettability properties of waxy leaves, on the other hand, allow geckos to establish a sturdy grip, even in rain storms, because leaves actively repel water. Geckos performed equally well in wet and dry conditions on the leaf-mimicking surface, the researchers found.
How the geckos interact with surfaces depends upon a thermodynamic theory of adhesion, the authors conclude. These features are dictated by Van der Waals force, or the sum of attractive and repulsive interactions between gecko toes and the characteristics of the surfaces they come into contact with. So long as those attractive forces jibe, geckos are in luck for getting a grip on whatever surface they come into contact with, regardless of whether it’s wet or dry.
Using our whole-animal adhesion results, we found that wet surfaces that are even weakly [water repulsive] allow the gecko adhesive system to remain functional for clinging and likely locomotion as well.
Our findings suggest a level of versatility in the gecko adhesive system that previously was not accounted for and calls into question interesting evolutionary, ecological, and behavioral predictions.
In addition to shedding light on how gecko adaptations help the lizards cope with their natural environment, the authors think their findings may contribute to designing new synthetic gecko robots that may overcome real-life geckos’ wet glass Achilles’ heel, useful perhaps for cleaning skyscraper windows, spying on suspected terrorists, or simply changing a hard-to-reach light bulb.
March 21, 2013
Designing a robot that can easily move across loose terrain—say, a rover meant to traverse the surface of Mars—poses a unique engineering challenge: Wheels commonly sink into what engineers call “flowable ground” (mixtures of sand, soil, mud and grass).
Given the many biologically-inspired innovations in robotics, a team of researchers from Georgia Tech had an idea—to base a design on desert creatures such as zebra-tailed lizards that are able to scramble across a loose, sandy surface without slowing down. Their efforts allowed them to create this small six-legged device, presented in an article published today in Science, which can run across a granular surface in a way uncannily reminiscent of a reptile.
The research team, led by Chen Li, designed the device after studying the locomotion of various creatures and mathematically simulating the performance of different types of legs (varying in number, shape and length) in several distinct environments. They hope their research will spur the development of a field they’ve termed “terradynamics”—just as aerodynamics is concerned with the performance of winged vehicles in air, their field will study the motion of legged vehicles on granular surfaces.
To design their robot, they used these simulations to determine the exact leg lengths, movement speeds and levels of force that would propel devices across a loose surface without causing them to sink in too deeply. They then printed a variety of leg types with a 3D printer, and built robots to test them in the lab.
One of their most interesting findings is that the same types of design principles apply for locomotion on a variety of granular surfaces, including poppy seeds, glass beads and natural sand. Their simulations and real-world experiments revealed that C-shaped legs generally worked best, but that any type of bow-shaped limbs worked relatively well because they spread out the weight of the device over long (albeit narrow) leg surfaces as the legs come into contact with the ground over the course of a stride.
The applications of this kind research are broad: This particular robot, the researchers say, could be developed into a useful search-and-rescue or scouting device, while the principles derived from the field of terradynamics could be useful in designing probes to explore other planets in the future. They could also help biologists to better understand the how life forms here on earth have evolved to move across our planet’s surface.
January 24, 2013
Mr. Safina, a local guide working at Komodo National Park, took a particular relish in describing the way a Komodo dragon’s strong jaws can snap a man’s leg in two. He’d lived on Rinca – a speck of land off Indonesia’s Flores Island, and one of the five places Komodo dragons reside – his whole life, and he was used to the various horror stories that surfaced every now and then after a tourist wandered off the trail or a kid got ambushed while playing in the bush. Standing in front of an assembly line of water buffalo, deer and wild horse skulls – dragon chow – Mr. Safina laughed while gesturing to a row of little wooden crosses stuck in the nearby mud. On each stick, a date and a foreigner’s name was scrawled in white paint. “Those are tourist graves!” Mr. Safina joked. “No really, they’re actually just baby mangrove markers that tourists bought to restore the forest. Now, are you ready to go see the dragons?”
Like so many other tourists, for me, a trip to Indonesia was not complete without a detour to see the world’s largest lizard in its natural habitat. (Read Brendan Borell’s dispatch from his trip to Komodo Island, as featured in our special “Evotourism” issue of Smithsonian magazine.) In recent years, visitors have increasingly flooded this corner of Indonesia, drawn in by the thrill of brushing close to something wild and dangerous. Dragons are not to be taken lightly: male lizards can grow up to 10 feet long, weigh 150 pounds and eat up to 80 percent of their own body weight in one sitting. Though attacks are exceptionally rare, they do occasionally occur, mostly when a park guard lets his focus slip for a moment, or a villager has a particularly unlucky day.
Here are some of the most infamous attacks, as described by Mr. Safina and corroborated by media reports:
A Tragic Playdate
In 2007, a dragon killed an 8-year-old boy on Komodo Island, marking the first fatal attack on a human in 33 years, the Guardian reported. The attack took place in March’s dry season, so rangers speculate that the murderous lizard may have been particularly hungry given that the watering holes – and the prey that gather there – had dried up. The dragon lunged when the boy went behind a bush to use the bathroom, MSNBC writes.
Mr. Safina recalls the boy’s friends – who had been playing together in the scrubland near their village – rushing to get help from their parents. According to the Guardian, the boy’s uncle came running and threw rocks at the lizard until it released his nephew. While the Guardian writes that the boy died from massive bleeding from his torso, Mr. Safina recalls the boy being bitten in half.
In light of the tragedy, park wardens launched an island-wide hunt for the man-eating lizard, though whether or not these efforts produced results remains unclear.
Shipwrecked with Dragons
In 2008, a group of SCUBA divers found themselves swept from waters near their boat by the Flores region’s infamously strong current. After spending 10 hours spinning in the tide, around midnight the group washed up on the beach of what seemed like a deserted island, approximately 25 miles from where their ordeal had begun. Their troubles, however, were far from over. They had found their way to Rinca Island, where an estimate 1,300 dragons live.
The attacks began almost immediately, the Telegraph reports. A relentless lizard repeatedly came at a Swedish woman, who smacked it with her diving weight belt. It chewed at the lead belt while other divers threw rocks at its head, she said, all the while eyeing her bare feet.
For two days and two nights, the traumatized divers contended with dragons and the tropical heat, surviving off of shellfish they scraped from rocks and ate raw. Finally, an Indonesian rescue crew spotted the diver’s orange emergency floats spread out on the rocks. Though in shock, the group rehydrated at the local hospital on Flores Island and celebrated their survival at the town’s Paradise Bar.
Death in the Garden
In 2009, 31-year-old Muhamad Anwar set out to gather sugar apples from an orchard on Komodo Island. A misstep that sent him falling from the tree proved to be his undoing. Two Komodo dragons were waiting below, and sprang on Anwar. His neighbors heard the commotion, and ran to his rescue minutes later. By the time they arrived, however, Anwar had already suffered fatal injuries, and was bleeding from bites to his hands, body, legs and neck, the Guardian reports. Anwar died shortly after the attack, in a clinic on Flores Island.
Other accounts, however, contest some of these details. CNN writes that Anwar – a fisherman – was actually trespassing on the island, and was in an area forbidden for people to enter. This account also reports that Anwar bled to death on the way to the hospital, and was declared dead upon arrival. Even if CNN got this right and Anwar was guilty, however, death by dragon seems an overly steep punishment for eating a bit of forbidden fruit from the garden of Komodo.
Dragon Under the Desk
In 2009, Maen, a fellow guide like Mr. Safina, headed to the staff office as he would any other morning. Like all the other buildings on Rinca Island, Maen’s unit sat on stilts, and hungry dragons would often gather below to wait for the occasional food scrap. On this morning, however, Maen sensed that he was not alone. Just settling in at his desk, he looked down. At his sandled feet lay a dragon, peering back up at him.
As it turned out, one of the cleaning crew had left the office door open the night before and the hungry predator had crept in, likely in search of food. Heart pounding, Maen attempted to slowly withdraw his leg from the dragon’s vicinity. But he moved too quickly, cueing the motion-sensitive carnivore to lunge. The dragon chomped down on Maen’s leg, clenching its jaw shut. Maen kicked at the dragon’s neck, then grabbed its jaws with his hands and wrenched its mouth open, slicing open his arm in the process.
Although Maen shouted for help, most of the rangers were in the cafeteria and could not hear his screams. Only one picked up on the noise, and came to investigate.
“I shouted and he came to help me but he didn’t like to come up because the dragon was still moving around,” Maen explained to travel writer Michael Turtle, of Time Travel Turtle. “Then he saw the blood on the floor and he got everyone from the kitchen. All the people come running here, but other dragons follow along as well.”
The dragons – which can smell blood and the scent of death from nearly 6 miles away – followed the crowd. Some rangers fended off the would-be feeding frenzy, while a couple others darted into Maen’s office to help their colleague fight free from his attacker. Maneuvering their injured friend through the pack of dragons waiting outside, they managed to carry him to the island’s dock, where he was rushed to Flores Island’s hospital. The injuries were too much for the small medical center to contend with, however, and Maen wound up being flown to Bali for six hours of emergency treatment and 55 stitches, MSNBC reports. All in all, it took him six months to recover from his brush with the dragon.
Despite the encounter, Maen went back to work, although he only stays indoors now so he does not have to deal directly with the animals. “The dragon, I can’t remember which one, he’s still alive,” he told Turtle. “But I think now he’ll be bigger. If he had a bigger neck then, I couldn’t have hold it open.”
Horror in Hollywood
Dragon attacks can occur outside of Komodo National Park, too. More than 50 zoos around the world keep the animals as attractions. In 2001, Phil Bronstein, an investigative journalist formerly married to actress Sharon Stone, suffered an unfortunate encounter with a Komodo dragon at the Los Angeles Zoo. Stone had arranged a private visit to the zoo’s dragon pen as a present for her husband, who, according to a Time Magazine interview with Stone, had always wanted to see a Komodo dragon up close. Stone described the incident:
Phil didn’t know where we were going or why we were going there. It was a complete surprise. So we came around the corner and he was like, ‘Oh my god this is so fabulous, I’ve always wanted to see this.’ And the zookeeper said, ‘would you like to go in the cage? It’s very mild mannered. Everybody goes in there. Kids pet him. It’s fine.’
Bronstein accepted the invitation and went into the dragon’s cage with the zoo keeper. The lizard began licking at Bronstein’s white shoes, which the keeper thought must remind the animal of it’s white rat meals. Following the keeper’s advice, Bronstein removed his shoes and socks to avoid tempting the lizard. Then, as he moved into a better position to take a photo with the animal, it lunged.
So there was that hideous moment where the three of us… It’s such a break in reality, it’s so inconceivable that it’s happening, but there’s that moment of stillness where you just stare in disbelief. Then Phil screamed and we heard this crunching sound.
Bronstein managed to pin the lizard’s head down with his other foot, but the animal began jerking back and forth in an attempt to maul and eat its prey. Children gathered around the cage’s glass wall, Stone recalled, taking in the spectacle.
Bronstein managed to wrench the dragon’s jaw’s open and throw it from his foot, then dragged himself out of the cage as the lizard came at him from behind. The top half of Bronstein’s foot was gone, Stone said, and he was covered in scratches from the animal’s lunges at his back. Bronstein survived the incident and did not press charges, though Stone complained that the zoo allegedly continued to allow close-up encounters with dangerous animals following the incident.
May 1, 2012
We live in an age of alarming extinction, in which many species are lost in large part due to human activity. At the same time, the natural world is so complex that even after centuries of research, scientists are still rapidly discovering new species everywhere from mountain tops to rain forests to the ocean floor.
This paradox is aptly illustrated by an announcement made yesterday: 24 new species of lizards, known as skinks, have been discovered in the Caribbean islands. But half of them may be close to extinction, and some may already extinct in the wild.
The research was conducted by a team led by Blair Hedges, a biologist at Penn State University and one of the world’s foremost experts at identifying new forms of life. Previously, Hedges has been involved with the discovery of what were then the world’s smallest snake, lizard and frog. The two dozen species named in this paper, published in the journal Zootaxa, constitute one of the largest mass discoveries of lizards in centuries.
To identify the many species of skinks (formally, members of the family Scincidae), Hedges and his team examined specimens housed at zoos and conservation centers around the world. By comparing taxonomic features of the lizards (such as the shapes of scales) and using DNA analysis, they determined that there are a total of 39 distinct species of skinks that live in the Caribbean—6 species that were previously recognized, 9 that had been named long ago but had been considered invalid and the 24 entirely new ones.
“Now, one of the smallest groups of lizards in this region of the world has become one of the largest groups,” Hedges said in a press release. “We were completely surprised to find what amounts to a new fauna, with co-occurring species and different ecological types.” He has determined that the skinks came to the Americas roughly 18 million years ago, likely arriving from Africa on floating rafts of vegetation.
How did the skinks go unnoticed for so long? Hedges speculates that because large numbers of skinks had already disappeared by the start of the 20th century, scientists, tourists and local residents have been much less likely to encounter them in the years since. Additionally, many of the characteristics that distinguish the species from one another have been overlooked or weren’t detectable until now, especially those indicated by DNA analysis.
The researchers determined that the skinks have long been most threatened by an exotic intruder: the mongoose, introduced from India to Cuba in 1872 with the intention of reducing rat populations in sugarcane fields. Rat populations were partially controlled, but by 1900, nearly half of the islands to which the mongoose had spread were also without skinks, and the remaining lizards have dwindled in population ever since. Additionally, the researchers note, current human activities such as forest removal are likely contributing to the skinks’ endangered status. The research team hopes that their data will be used to plan future conservation efforts.
Theoretically, if you’re in the U.S. Virgin Islands, Trinidad and Tobago, or Martinique, you might try looking for a skink. But because each of the species is remarkably rare—with even the non-endangered ones qualifying as vulnerable—it’ll certainly be difficult. Above all, if you do want to find one, hurry up: there may not be much time left.