No Surrender: Monkeys Fight Back Against Predators, But At What Cost? One May morning in 2009, a group of white-faced capuchins were foraging on a hillside on Barro Colorado Island, Panama. Two researchers from the Smithsonian Tropical Research Institute, Anyuri González and Lucia Tórrez, were watching the group from nearby, but when one of the monkeys started shrieking, they realized they weren’t the only voyeurs.

The screams were an alarm call indicating a predator on the ground. The group’s alpha male took off in the direction of the noise and was joined several other adult members of the group, and they all began making facial and vocal threats and shaking and throwing branches toward a dense tangle of liana vines.

There was something in there, and the monkeys didn’t like it.

Mob Rules

While many animals go to great lengths to hide or flee from predators, some animals take the opposite tack and confront their attackers. Some species of primates, birds, fish and squirrels will harass and assault potential predators with mobbing behavior that involves loud vocalizations and physical attacks at close range.

The mobbing of a predator by capuchins is a real sight. Led by adult and subadult males, the monkeys will make loud threat and alarm calls while breaking large branches from trees and dropping them on the predator like bombs.

Researchers have been mistaken as predators themselves and received blows – at least one admitted to being knocked unconscious – from branches broken and dropped over their heads. Scientists working in capuchin territory quickly learn to to stop taking data and get out of the way when they see a monkey scanning the canopy directly above them, a sign that its looking for a branch that it will be able to break.

Some monkeys will get closer to predators if the aerial assault doesn’t work. In 1988, biological anthropologist Susan Boinski watched as a group of capuchins in Costa Rica killed a terciopelo, or fer-de-lance, after pinning it to the ground with a heavy branch and then approaching on the ground to beat it with sticks. One monkey rained down a flurry of 55 strikes to the snake’s body and head with a stick that it clumsily wielded like a club. Boinsky later approached the snake and found a mangled mess of bleeding wounds, exposed tissue and broken bones.

A Death in the Family

As González and Tórrez watched, a sense of alarm spread through the capuchin group. Juvenile monkeys and an adult female with a clinging infant gathered some distance away from the liana tangle, while the rest of the adults joined the alpha male on the frontline.

The capuchins’ alarm calls intensified and González, who was downwind from the liana tangle, noticed a distinct smell. A cat. She could see the right side of whatever was in the liana, and based on its size and fur color and patterns, decided it was not one the ocelots normally seen on the island, but a jaguar visiting from the mainland.

The cat growled loudly, making the capuchins visibly nervous. They glanced repeatedly at one another and one of the adult females retreated to where the juveniles were waiting. Together, they moved further away from the liana. The jaguar growled again and moved around in its hiding spot, and most of the remaining capuchins also retreated.

As far as González and Tórrez could see, only six adult and subadult males remained near the liana tangle, and their vocalizations had decreased in both frequency and intensity. They looked back and forth at one another and then moved silently away from the jaguar, following their groupmates.

Only one monkey stayed behind, and continued to make alarm calls. González and Tórrez weren’t able to see the monkey, and as they attempted to get close enough to verify which one it was, the cat made a very loud, very aggressive growl, and the researchers decided to retreat a little themselves.

From a safer distance, they could still hear the lone capuchin making alarm calls. Then, there was the sound of sudden movement and the rustling of branches. The alarm calls stopped and they heard two weak moans.

After that, there was only silence.

González and Tórrez encountered the capuchin group later that morning. The group was quiet, and had returned to foraging for insects. They took a headcount and found that one of the subadult males, named LK, was missing. Every other group member was accounted for but LK was not seen again over the course of their study.

At What Cost?

Approaching and mobbing predators appears to invite some obvious risks, as LK’s death shows. The true costs of mobbing are hard to suss out, though, because reports of primates being injured or killed while mobbing are very rare. The LK incident is, as far as González, Tórrez and their colleagues know, the first documented fatality arising from a mobbing event.

With limited observations, researchers have hypothesized several risks. The risk of injury and/or death seems to depend somewhat on the predator. Many snakes are cryptic hunters, and, once discovered, will freeze and can be mobbed with relatively little risk. Other predators, like large cats, continue to pose a significant threat to monkeys even after they’ve been discovered, and some will even chase their prey into the trees, giving them no quarter.

There are also other less grisly losses to consider, like the effort that goes into fighting back and opportunity costs of taking time from other activities. Some monkeys have been known to remain at the site of a spotted, attacked or even injured or dead predator for up to two hours after mobbing. That’s time and energy that could be spent foraging or mating sacrificed to a risky behavior, and even a “win” for mobbers might compromise the animals’ health and reproductive success, making it a Pyrrhic victory.

Figuring out the costs of mobbing, in turn, would help explain its benefits. If the price that primates are willing to pay to harass their predators are as large and varied as they seem, the rewards should be enough to make the risk worthwhile.

The obvious benefit of mobbing for social primates is that chasing off or killing predators helps protect their social group, relatives, mates and offspring. It’s also possible that mobbing events act as a learning opportunity for younger monkeys. Juveniles are able to study the animals that provoke alarm calls and defensive behavior and compare them to animals that don’t, and learn to know danger when they see it.

Another benefit to mobbing may be that, because it is so costly, it acts as an honest signal of an individual monkey’s quality as a mate. Attacking a predator gives a monkey the opportunity to display their physical condition, agility, and speed. Mobbing might be a way for females to evaluate the ability and willingness of males to protect them and their future offspring against threats.

Unfortunately, with so little data from the field or the lab, we don’t know how often mobbing ends lethally, or the likeliness of a fatal attack when a primate does vs. doesn’t mob, so it’s hard to weigh the costs and benefits that play on a monkey’s decision to stand its ground or retreat, maybe to fight another day.

S. Boinski (1988). Use of a Club by a Wild White-Faced Capuchin (Cebus capucinus) To Attack a Venomous Snake (Bothrops asper) American Journal of Primatology, 14 (2), 177-179 DOI: 10.1002/ajp.1350140208

Tórrez, L., Robles, N., González, A., & Crofoot, M. (2012). Risky Business? Lethal Attack by a Jaguar Sheds Light on the Costs of Predator Mobbing for Capuchins (Cebus capucinus) International Journal of Primatology, 33 (2), 440-446 DOI: 10.1007/s10764-012-9588-1

Dugatkin, L., & Godin, J. (1992). Prey approaching predators: a cost-benefit perspective. Ann. Zool. Fennici, 29, 233-252

Lloyd, E., Kreetiyutanont, K., Prabnasuk, J., Grassman, L., & Borries, C. (2006). Observation of Phayre’s leaf monkeys mobbing a clouded leopard at Phu Khieo Wildlife Sanctuary (Thailand) Mammalia, 70 (1/2), 158-159 DOI: 10.1515/MAMM.2006.028

Caro, T. Antipredator Defenses in Birds and Mammals. University of Chicago Press. 2005.

Fragaszy, D., Visalberghi, E., Fedigan, L. The Complete Capuchin. Cambridge University Press. 2004.

Images: “Deux capucins moines Cebus capucinus” by Jean-Baptiste LECA & Noëlle Gunst. Public Domain. “Jaguar at the Belieze Zoo” by Bjørn Christian Tørrissen, used under a Creative Commons License.




Loud Fly Sex Means Death by Bat One of the unspoken rules of slasher movies is that sex means death. Teen hookups are like a siren song to B-movie killers, and as soon as a pretty, young supporting character loses her virginity, she loses her head. A new study shows that sex might also be a death sentence for some flies, as it attracts the attention not of a knife-wielding psycho, but bats.

Where there’s cows, there’s manure. Where there’s manure, there’s flies. On many farms in Germany, there’s also Natterer’s bats (Myotis nattereri), which flock to cow sheds for the convenient feast. Scientists couldn’t figure out how the bats got their meal, though. Bats usually hunt by echolocation, sending out a series of high frequency calls and finding prey based on the echoes that bounce back. It’s great for finding bugs in mid-flight, but less so when they’re sitting still or just walking around. It’s especially hindered in the cow sheds, where the roughly textured wall and ceiling surfaces almost completely mask the flies’ weak echoes. Over four years, a team of researchers led by Björn M. Siemers from the Max Planck Institute for Ornithology filmed thousands of flies in a shed in Weitershausen, Germany. The flies wisely refrained from flying at night, and when they walked over the walls and ceiling, not a single one of them was ever hunted by the 45 bats that lived there.

As soon as the flies started having sex, though, the bats embraced their inner Michael Myers and attacked the love-making couples. The researchers found that a quarter of mating flies were preyed on and over half of those attacks were successful, with the bat devouring both partners in all but two instances.

What is it about sex that got the bats’ attention? When the researchers stuck dead flies together in a morbid post-mortem sex simulation, they were ignored, so it isn’t the more conspicuous echo that a mating pair creates. Instead, the researchers suggest that its the sweet sounds of fly love that dooms them.

During sex, the female fly spreads her wings while the male flutters on top of her. This creates a series of clicks between 9 kHz and 154 kHz. We hear the lower end of that as a buzzing sound, but the higher pitches are loud and clear to the bats. When the researchers played a recording of the sexy soundtrack, the bats attacked the speakers, but not when they played other noises at the same frequency band and amplitude, suggesting that those specific sex sounds are important prey cues that ring like a dinner bell for the bats.

If all that noise means a fly winds up in a bat’s stomach post-coitus, one would like to think that there would be strong natural selection against it. The researchers say that the fact that it continues despite predation pressure suggests that might be a courtship element and a signal of the males’ quality as mates and fathers. The noise is perhaps an integral step to getting it on, important enough to run the risk of being noticed by a killer lurking in the shadows.

Reference: Björn M. Siemers, Eva Kriner, Ingrid Kaipf, Matthias Simon and Stefan Greif (2012). Bats eavesdrop on the sound of copulating flies. Current Biology, 22 (14), 563-564 DOI: 10.1016/j.cub.2012.06.030

Image: Myotis nattereri” by Guido Gerding. Used under a Creative Commons License.


For snakes, hunting bats in a cave is like shooting fish in a barrel

When the sun goes down in the subtropical forests of Puerto Rico, hundreds of thousands of bats emerge from the caves that stud the island’s northern end. After a day of sleeping, the animals are ready for a hard day’s night of hunting insects. For some of them, though, there will be no feast of beetles and mosquitos, and they’ll instead wind up a meal themselves for the snakes that have set up an ambush at the cave’s entrance.

After providing a warm, safe place to sleep all day, the caves become death traps once darkness falls. Puerto Rican boas slither in from all over the forest to turn the bats’ exodus into their own hunting ground. At the mouth of the caves, they lay on the ground, cling to roots and vines on the walls or hang down from the ceiling, their tails finding footing in the tiniest cracks and crevices. As the bats flit past them on all sides, the snakes wait, swinging like clock pendulums. When a bat brushes by or collides with a snake’s head, the snake grab it in its jaws, squeeze it in its coils and eats it whole.

The nightly ritual is played out on its largest scale at La Cueva de Los Culebrones, or the Cave of the Long Snakes. The cave’s estimated 300,000 bats can empty out in as little as three hours, providing the boas with an all-you-can-eat bat buffet. Biologists observers have seen as many as 20 boas hanging around the cave entrance, grabbing all the bats as they care to and chowing down.

Even with the steady stream of food flying right into their mouths, the snakes can be picky, and competitive. Several species of bats can inhabit the same cave, and the smaller ones tend to exit first. Although the snakes are in position and waiting as soon as the first bats, they often wait half an hour to an hour to start hunting, when the larger bat species take flight. This might be a strategic choice to save their energy for prey that gives them more calories in reward for their effort.

Sometimes, a snake that’s not having any luck with its own hunting will attempt to steal a bat from another snake. On one occasion, a biologist watched three snakes fight over a large bat carcass for over an hour and a half. By the end of it, the snakes were exhausted and the bat went uneaten.

Last summer, Neil Losin and Nate Dappen, a pair of biologists and filmmakers who run Day’s Edge Productions, were in Puerto Rico and heard stories about the snakes, and had to see and film it for themselves. The resulting video, Snakes in a Cave, is awesome, and captures some closeup, slow motion bat snatching action.

Snakes in a Cave from Day's Edge Productions on Vimeo.

Reference: Rodriguez-Duran, A. (1996). Foraging Ecology of the Puerto Rican Boa (Epicrates inornatus): Bat Predation, Carrion Feeding, and Piracy Journal of Herpetology, 30 (4) DOI: 10.2307/1565698


Giving up trash for Lent: How a human custom forces hyenas to hunt

ResearchBlogging.orgAll over the world, the expansion of urban areas and other human activities has pulled the natural prey base out from under many ecosystems and brought large predators in close contact with people and the resources they can provide – livestock, garbage, unattended pets, etc.. Many predators will take advantage of these food sources, often leading to human-animal conflicts (see wolves in the western U.S., lions in Africa and a range of others). Sometimes, though, humans and wild carnivores will become fairly friendly neighbors.

On the Horn of Africa, spotted hyenas (Crocuta crocuta) have adapted well to dense human populations, and the two species have a unique relationship that benefits both of them. The hyenas almost never attack people and mostly leave their livestock alone, preferring to scavenge on waste and refuse from homes and businesses. The hyena’s iron stomach helps them fit in well here, and they can choke down almost any organic matter they find at the dump – from leftover porridge, to feces, to putrid, anthrax-infected carcasses. The people aren’t exactly thrilled with the hyena presence, but many villages and towns tolerate them as walking garbage disposals. The locals call them “municipal workers,” and refrain from harassing or killing them.

Every year in the spring, this arrangement collapses when members of the Ethiopian Orthodox Tewahedo Church celebrate the fasting period of Lent. For 55 days leading up to Easter, Ethiopian Christians abstain from meat and other animal products, which causes a slow couple of months for the local butchers, and a dearth of carcasses at the dumps.

Without the fat of the land to live off of, what’s a non-Christian hyena to do? Gidey Yirga from Ethiopia’s Mekelle University and colleagues from Africa and Europe observed the animals during last year’s Lent and found that thy turn to hunting instead. Despite their reputation as strict scavegners and opportunists, hyenas are formidable, efficient hunters. Stalking alone or in packs, they favor large prey (150-400 pounds) and a lone adult hyena can take down an animal four times its own size. In East African ecosystems where scavenging opportunities are rare, they hunt and kill 60–95% of their food.

Last spring, Yirga and his team went to three different sites around the city of Mek’ele and collected all the hyena droppings they found on the first day of Lent, the last day of Lent and 55 days after that. Several months worth of dropping gave them a glimpse of what the hyenas were eating before, during and after the fasting period. There isn’t much to be found in a hyena turd, since they can digest pretty much all parts of their prey except hair, hooves and a few inorganic components found in bones. It was enough for the researchers to go on, though, and they compared the hair from the 553 droppings they found to hairs from a reference collection to ID the animals the hyenas had been eating.

The scat studying revealed that before and/or after Lent, most of the hyenas’ diet is made up of goat, sheep, horse and cow – usually scavenged waste parts. While humans are fasting, though, the hyenas scavenge less (while the butchers’ supply dried up, the local veterinary school still provided some carcasses) and fill the gaps in their menu by actively hunting donkeys. The donkey is a natural choice of prey if an urban hyena has to go after a live animal. They’re the right size and, unlike the other local livestock, they’re not kept penned in in compounds. They’re easy pickings, and during Lent, the hyena’s donkey consumption can double from surrounding weeks.

Faced with a carnivore’s dilemma, the hyenas showed how adaptive they can be to the sometimes strange behaviors of their human neighbors. Yirga’s study is not only evidence of the hyena’s versatility, but also highlights trash as a delicate factor in urban carnivore management. If you give predators an inch, they’ll take a mile, or a donkey, and better waste management would create a less inviting environment for them. In areas where wild carnivores have grown dependent on livestock and garbage for lack of other prey, though, a too-tight lid on the garbage can could thin their numbers and have an ecological ripple effect.

Hat tip to Barbara J King for bringing the study to my attention. 

Reference: Yirga, G., De Iongh, H., Leirs, H., Gebrihiwot, K., Deckers, J., & Bauer, H. (2012). Adaptability of large carnivores to changing anthropogenic food sources: diet change of spotted hyena (Crocuta crocuta) during Christian fasting period in northern Ethiopia Journal of Animal Ecology DOI: 10.1111/j.1365-2656.2012.01977.x

Images: “Portrait of a Spotted Hyena” by Marieke Kuijpers. “Spotted Hyenas, Crocuta crocuta, at carcass of an Impala” by Jerry Friedman. Both used under a Creative Commons License


Search and Destroy: Sawfish are handier with their blades than previously thought

With their long, serrated snouts, the sawfish might strike you as a little like aquatic versions of Leatherface. Scientists used to think the two were behaviorally comparable: sluggish and maybe a little dimwitted, just waving their saw around blindly and waiting for something to run into it. New research by Barbara Wueringer and colleagues from Australia and the US, though, shows that the fish actually wield their saws with considerable skill. They’ve also learned that the sawfish’s nose knows, too, and is a complex sensor as well as a weapon.

The sawfish family has not been heavily studied (a shame considering that all seven species are endangered), and with only a few firsthand accounts of how the fish hunt, researchers could only speculate on how the saws were used. One of the more common suggestions was that they were bottom feeders and raked their snout through the sand to snag buried prey on the saw’s teeth. Other ideas were that the fish cut into the sides of whales or slashed their way through schools of fish.

To figure out what was really going on, Wueringer and her team captured young freshwater sawfish in northern Australia and watched them feed on mullet and pieces of tuna. The fish went after the food in two different ways, depending on whether it was floating in the water or lying at the bottom of the tank. In the water, they quickly slashed at the prey to impale it on their saws’ teeth or knock it to the bottom or into position to eat. Some of these strikes were strong enough to cleave the fish in half. At the bottom of the tank, the sawfish used the underside of their saws to pin prey down and then move them into position to ingest, and usually preferred to eat the mullet headfirst. This video shows all of these maneuvers.

The sawfish weren’t just spearing wildly, either, and the study found that their snouts are part lance and part smart missile, with buit-in tracking systems. Sawfish are closely related to rays, skates and sharks, and share their sensitivity to electrical fields and their ability to use them to navigate and detect other animals.  Wueringer discovered a few years ago that sawfishes’ saws are covered in electroreceptors, and when she presented the sawfish in this new study with electrodes that mimicked the electric signals prey would give off, the fish reacted the same way they did to the food.

The sawfish’s saw has turned out to be more impressive than anyone thought, but cause the fish a lot of trouble, too. Every sawfish species is listed as Critically Endangered by the IUCN Red List, in part because their saws are prized by shamans in Asia as tools for expelling demons and disease, and are easily caught on fishing hooks and lines.

Reference: Barbara E. Wueringer, Lyle Squire, Stephen M. Kajiura, Nathan S. Hart, & Shaun P. Collin (2012). The function of the sawfish’s saw
Current Biology, 22 (5), 150-151 : 10.1016/j.cub.2012.01.055

Image: “What a saw” by Lorenzo Blangiardi. Used under a Creative Commons license


Slithering through history: Snakes have been primates’ predators, prey and competition

ResearchBlogging.orgIn pre-colonial Mexico, the winged serpent Quetzacoatl was worshipped as a god. In modern-day Texas, rattlers are regularly fried and eaten. And in Pennsylvania, the snakes at the Philadelphia Zoo’s reptile house have quietly gone about their business while my girlfriend stood in the corner, eyes squeezed shut, shaking with fear.

People’s feelings toward, and relationship with, snakes have varied greatly depending on the time period, location and culture. Today in the U.S., if fear isn’t the most common reaction (it was our #1 fear 10 years ago), then it’s at least very high profile…

You might assume it’s an old fear, too. Certainly our ancestors, whether two hundred or two million years ago, encountered snakes more often than most of us do. In a new study published this week in Proceedings of the National Academy of Sciences, anthropologist Thomas N. Headland and ecologist Harry W. Greene suggests that pre-modern humans and the lower primates have indeed had a long shared history with snakes, and its more complex than we had thought. Because constrictors usually swallow their prey whole and intact and venomous snakes attack soft tissue, there’s almost nothing in the fossil record to tell us anything about snakes attacking and/or eating humans and other primates. To figure out the relationship extinct hominins and pre-modern humans might have had with snakes, examining bones wouldn’t cut it, so the Headland and Greene had step back in time, in a way. [Read more]


Night of the Bargain Hunter: some bats pick prey based on the cost of the hunt

While they’re less likely to occupy Wall Street than a barn upstate, bats are as concerned as we are about the economy. Their economy revolves around energy instead of money, though, and a problem on the balance sheet can be a matter of life and death. If they spend more energy catching a meal than that meal provides, they’ve created an energy deficit that impacts their health, growth and survival.

There’s no need to worry about bats during a recession, though. New research from biologists in Germany suggests that bats are actually pretty savvy shoppers and are able to use echolocation to make economic decisions while hunting and stay in the black, calorically speaking. [Read more]


Good Webkeeping: Spiders use Decorations as Defense
Orb-weaving spiders are those spiders that build the spiral wheel-shaped webs that we often tend to think of as the Platonic ideal of spider webs. The ones you find draped between two dewy branches in a sun-dappled meadow, spider sitting in the dead center lying in wait for hapless flys and other insects to collide with the nearly invisible, impossibly sticky threads and get trapped.

While this technique keeps the spiders’ bellies full, it’s not without its problems. Those of us who’ve walked through a doorway or between two tree branches only to come away covered in thin, sticky web threads know that it’s not pleasant (for me, it is the stuff of nightmares). For the spider, it’s absolutely disastrous. Severe damage to the web by humans and other animals that the spider has no intention, or hope, of devouring costs them the production of more silk for a new web, exposure to predators, lost hunting opportunities and missed meals, and ultimately plays with the odds of their survival.

What’s a spider to do, then, when getting through the day requires a web that’s inconspicuous enough that prey don’t notice it, but has enough presence to warn animals that would just wreck it?

The species of the genus Argiope pull off a contradictory, but seemingly necessary, signaling paradox by constructing “decorations” of zigzagging bands of silk on their webs. They make the web very conspicuous to the naked eye, even from a distance, but don’t seem to tip off prey insects that they’re about to stumble into a trap. [Read more]


Cannibal Crickets Can Control a Crowd: How Eating Your Friends Aids Collective Motion
On the wide, open plains of the American West, it’s more than the buffalo and the antelope that roam. Mormon crickets (Anabrus simplex) also sweep across the land in huge migratory swarms that can stretch six miles long and three miles wide. The crickets (a misnomer, they’re actually flightless katydids) can march up to a mile and a quarter a day in these groups, devouring every scrap of vegetation in their path and devastating agriculture in areas they pass through.

It sounds like a Biblical plague*, but consider the poor crickets. While the swarming behavior isn’t completely understood, entomologists think that it’s partly a strategy to avoid being eaten. Observations and experiments have shown that crickets that become separated from the group are easy prey and a big, cohesive group minimizes the risk of predation for any individual cricket.

Not that life in the swarm is any easier. In addition to consuming any and all plants they come across, the crickets often eat each other. One reason for this should be obvious, says a new study, “huge, concentrated numbers of crickets require huge, concentrated amounts of food. If the landscape doesn’t provide it, a fellow cricket will.”

A not so obvious side effect of this crickety cannibalism is that it might be helpful, even necessary, in keeping the swarm moving as a unit. A swarm of insects is simply the sum of its parts. The group’s movement, coordination, cohesiveness and persistence are the simple decisions and interactions of millions of individuals scaled up to the population level, and some of those decisions and interactions happen to involve one insect eating another. Another swarming insect, the desert locust (Schistocerca gregaria), tends to cannibalize traveling companions that have stopped moving or can’t keep pace with the group, and the threat of cannibalism influences their marching behavior. Individuals keep moving and maintain proper direction and pace to keep from becoming lunch for the guy behind them, and this helps maintain coherent swarm motion. [Read more]


Man of Steel: Armor, not weapons, protects harvestmen from certain doom

A lot of people mistake harvestmen for spiders, but there are two big differences between the two orders of arachnids. One, harvestmen do not scare the living shit out of me and I do not need to my girlfriend to kill any that wander into our house. Two, the eight-legged freaks commonly called daddy longlegs are awesome beyond your wildest imagination, whereas spiders are demons from Hell and are not awesome.

Among the 6,400 known species of havestmen, there are females who can give birth without the need for a male to fertilize thier eggs. There are males who mate with multiple females and then guard all the eggs, sometimes from egg-eating females they’ve recently mated with. There are harvestmen who enjoy each other’s company so much that they live together in groups of 70,000+ individuals. Then, there’s the granddaddy of wieners, willies, dongs and johnsons, the 400-million-year-old fossilized harvestman that possesses the world’s first known penis.* [Read more]