Tag Archives: predators

Some fish start Mexican waves to keep themselves safe from predators

New research reports that at least one species of fish engages in similar behavior to sports fans — collective waves.

Kingfisher bird with Sulphur molly. Image credits Juliane Lukas.

It’s not uncommon to see collective — also known as ‘Mexican’ — waves on arenas hosting football (soccer) matches around the world. These involve large groups of fans successively standing up in unison, as a display of solidarity between them and for their favorite teams.

Sulphur mollies (Poecilia sulphuraria), however, do it for a completely different purpose. A new paper describes this incredible collective behavior in the wild fish species, detailing how hundreds of thousands of individuals coordinate, likely to protect themselves from predatory birds.

Stronger together

“At first we didn’t quite understand what the fish were actually doing,” said David Bierbach, co-first author of the study. “Once we realized that these are waves, we were wondering what their function might be.”

The study showcases just how many of the fish partake in such behavior — there can be up to 4000 fish per square meter of ‘wave’, and each can include hundreds of thousands of individuals, according to the team.

Sulphur mollies are small animals, who stand out due to their preferred environment: sulphuric springs whose chemical make-ups make them toxic to most other species of fish.

The team explains that they likely use this living wave behavior as a way to confuse or maybe deter predators, especially birds. Mollies engage in this behavior when a person’s shadow falls on the water as well, further reinforcing this hypothesis. Individual waves last three to five seconds each, but the mollies have been recorded as repeating the behavior for up to two minutes.

The team first had to rule out the possibility that this behavior was random — their experiments showed that the fish would engage in ‘waves’ in a conspicuous, repetitive, and rhythmic fashion in response to stimuli associated with the presence of predators.

Then, they examined whether this behavior had any effect on the predators themselves: it does. The team reports that experimentally-induced fish waves dramatically reduced the frequency of attacks from birds of prey, and doubled the time these birds took between attacks. For one of their predator species (kiskadees, Pitangus sulphuratus), wave patterns also decreased capture probability.

Birds exposed to these wave patterns would switch perches more often than control individuals, suggesting that they may prefer to focus their attention on other prey when confronted with the mollies’ wave behavior.

According to the team, this is the first time a collective behavior has been shown to be directly responsible for reducing a species’ chances of being attacked and preyed upon. It is an important discovery for the study of collective behavior in animals more broadly, they add.

“So far scientists have primarily explained how collective patterns arise from the interactions of individuals but it was unclear why animals produce these patterns in the first place,” says co-author Jens Krause. “Our study shows that some collective behavior patterns can be very effective in providing anti-predator protection.”

Something that the team can’t yet explain is why such behavior helps protect the mollies from attacks. It’s possible that the motions confuse the birds, or perhaps they work as a signal to the bird that they have been spotted, making it consider another target altogether. The team plans to explore these questions in the future.

The paper “Fish waves as emergent collective antipredator behavior” has been published in the journal Current Biology.

Predators can learn what food to avoid from watching TV

New research from the University of Cambridge found that blue tits and great tits can learn to avoid unpleasant foods by watching their fellow birds eat on TV.

Two Blue Tits sharing food.
Image credits Dave Croker.

Seeing the ‘disgust response’ in their fellows helped the birds that took part in this study to avoid dangerous or unpleasant foods without having to try them themselves, the team reports. Later on, they recognize distasteful prey by their markings, potentially improving their survival rate.

The findings offer insight into how species share information regarding prey or food socially and help showcase the evolutionary benefits of banding together in groups or flocks.

Foodie shows

“Blue tits and great tits forage together and have a similar diet, but they may differ in their hesitation to try novel food. By watching others, they can learn quickly and safely which prey are best to eat,” said first author Liisa Hämäläinen, formerly a Ph.D. student at the University of Cambridge’s Department of Zoology and now at Macquarie University, Sydney.

“This can reduce the time and energy they invest in trying different prey, and also help them avoid the ill effects of eating toxic prey,”

The team worked with blue tits (Cyanistes caeruleus) and great tits (Parus major), in order to understand how and why prey avoidance behaviour spreads through populations of predators.

Blue tits and great tits forage together in the wild, so have many opportunities to learn from each other. If prey avoidance behavior spreads quickly through predator populations, this could benefit the ongoing survival of the prey species significantly, and help drive its evolution.

Many species of insects use bitter or toxic chemicals to deter predators. They usually advertise this with bright coloring and conspicuous markings. However, these ploys only work after a predator has learned to associate them with ‘undesirable’ prey. The findings of this study, however, shows that predators can learn which prey to avoid by watching other members of their group while trying to consume different insects.

The team showed each bird a video recording of another as it was eating distasteful prey. Some of the recorded birds displayed a disgust response (including vigorous beak wiping and head shaking) which the team hoped would help inform the watchers. This behavior was sometimes edited out to see if it would affect the watchers’ behavior.

The ‘prey’ shown on TV consisted of small pieces of almond flakes glued inside a white paper packet — some of these packets were soaked in a bitter solution. All packets had a marking on the side to help the birds better differentiate between them: a cross symbol that blended into the background for tasty packets, and a conspicuous square for the bitter ones.

When presented with these packets later on, the TV-watching birds (both blue tits and great tits) ate fewer of the bitter ones if they witnessed a disgust response to those packets in the footage, the team reports.

“In our previous work using great tits as a ‘model predator’, we found that if one bird sees another being repulsed by a new type of prey, then both birds learn to avoid it in the future,” said Dr. Rose Thorogood, who led the research.

“By extending the research we now see that different bird species can learn from each other too. This increases the potential audience that can learn by watching others, and helps to drive the evolution of the prey species.”

The paper “Social learning within and across predator species reduces attacks on novel aposematic prey” has been published in the Journal of Animal Ecology.

Alligator found sunbathing on an ocean beach in Florida. Credit: Duke University.

Why alligators on the beach and killer whales in the river is the new normal

Alligator found sunbathing on an ocean beach in Florida. Credit: Duke University.

Alligator found sunbathing on an ocean beach in Florida. Credit: Duke University.

Recently, more and more peculiar sightings of predators have been reported in places they’re not traditionally associated with. For instance, alligators have been spotted enjoying the sun on Florida beaches while killer whales have been seen swimming freely in freshwater rivers. At first glance, these shocking occurrences can be explained by successful conservation efforts that have improved predator populations — but there’s much more to it.

In a new study, researchers have found that as predator numbers rebounded, they’ve actually reclaiming what was rightfully theirs, reconquering habitats they called home before human activity drove them out.

“We can no longer chock up a large alligator on a beach or coral reef as an aberrant sighting,” said Brian Silliman, Rachel Carson Associate Professor of Marine Conservation Biology at Duke’s Nicholas School of the Environment.

“It’s not an outlier or short-term blip. It’s the old norm, the way it used to be before we pushed these species onto their last legs in hard-to-reach refuges. Now, they are returning.”

Home away from home

Silliman was once in a saltmarsh studying crabs and snails when he came across an alligator, which is a freshwater specialist. He was utterly shocked but as he learned of other similar sightings, the biologist spotted a pattern. Soon, it was clear that the alligators weren’t alone and that other apex predators, both on land and in water, were unconventionally moving into new territories.

By processing data from scientific studies and government reports, Silliman and colleagues learned that large predators were spotted into other territories. Examples include the movements of orangutans into disturbed forests, river otters into marine wetlands, wolves and coyotes onto beaches and rocky shores, and grey, harbor, and harp seals from the Arctic into subtropical waters. These places were actually part of the predators’ original habitat but human intervention drove them out, Silliman says.

“The assumption, widely reinforced in both the scientific and popular media, is that these animals live where they live because they are habitat specialists. Alligators love swamps; sea otters do best in saltwater kelp forests; orangutans need undisturbed forests; marine mammals prefer polar waters. But this is based on studies and observations made while these populations were in sharp decline. Now that they are rebounding, they’re surprising us by demonstrating how adaptable and cosmopolitan they really are,” Silliman said, who published the findings in the journal Current Biology.

The findings are good news. They suggest that large predators are more adaptable than previously thought. For instance, up to 90 percent of the diets of alligators found in seagrass or mangrove ecosystems consisted of stingrays, sharks, shrimp, and other marine species. As climate change intensifies, it’s important to know that some predators are more resilient than previously thought in order to plan conservation accordingly.

Climate change, for instance, threatens kelp forests which sea otters love but the animals are flexible enough to occupy estuaries which lack kelp forests. Moreover, the movement of large predators back into their historic ranges can be beneficial for ecosystems. The introduction of sea otters to estuarine seagrass beds helps protect the beds from being smothered by epiphytic algae that feed on excess nutrient runoff from inland farms and cities.

“It tells us these species can thrive in a much greater variety of habitats. Sea otters, for instance, can adapt and thrive if we introduce them into estuaries that don’t have kelp forests. So even if kelp forests disappear because of climate change, the otters won’t,” Silliman said. “Maybe they can even live in rivers. We will find out soon enough.”

Antlers.

Men trophy hunt to show off to the ladies, new research found

Why do some humans go after the biggest animals they can find? And how can these hunters be turned away from killing what are often endangered or threatened beasts? One trio of researchers found it’s all about bragging — or shaming.

Antlers.

Image credits Michael Bieri.

For a really long time in human history, supermarkets surprisingly weren’t a thing. So if you wanted some meat to go with your nuts, berries, and assorted veggies, boy you were in for an adventure — it was either hunting something alive or scavenging (which usually meant fighting something alive which had fangs). Long story short, it was dangerous, but we had to do it for the food.

There is one kind of hunting that flies in the face of this risk-reward dynamic animals have with subsistence hunting, however. Some human hunters go after the biggest, meanest, most dangerous animal around, even when they don’t want to eat it. Needless to say, such hunting can have devastating consequences for wildlife populations. So why do some people spend huge sums of money to kill big game that’s usually on the brink of extinction anyway? It doesn’t make any sense.

The answer, according to a trio of researchers, is sex.

What.

The fact that it doesn’t make sense is half the point here, the team explains. The other one is that it is expensive. Put them both together and what you get is “this costs a lot, I get nothing out of it, and now I am going to do it. Look how cool I am.” In short, it’s all about getting bragging rights. The pricey hunt is meant to show off a male’s high social status to competitors and potential mates. The theory would offer an evolutionary explanation for why humans kill animals they don’t need to, and suggests a possible tactic for discouraging that behavior in the future.

“Policy debate about [trophy hunting] benefits and costs focuses only on the hunted species and biodiversity, not the unique behaviour of hunters,” the authors write.

Lead author Chris Darimont, Hakai-Raincoast professor at the University of Victoria in British Columbia and his team describe human beings as “superpredators” because they’re not bound by the typical rules of other carnivores in the animal kingdom. The average predator “typically picks prey that are newly born (the juveniles) or nearly dead (the sick and weak animals, the substandard animals in populations) and they eat them,” they added. “And this really bizarre, unique predator, [the] human being, kind of does the opposite. We target the large; we target animals for characteristics that have nothing to do with their nutritional value; we target animals with big horns or antlers.”

To find out what evolutionary drive powers trophy hunting, the team compared this behavior to the habits of “traditional hunter-gatherers” — modern populations whose lifestyles resemble those of ancient humans. Darimont pointed out that in the Meriam population of Australia, men and women both hunt for green turtles but employ different methods.

We can do it the sensible way, or the right way

Ego.

Look at this handsome guy!
Image credits cortto / Flickr.

Whereas the women employ a safe and easy method, by capturing turtles who come ashore to lay eggs, men take a complicated, expensive, and dangerous route. They take to the sea on boats then dive in dangerous waters to hunt the same turtles on their own turf. Even worse, the men often have to share the meat they hunt with the community, rather than keeping it for their family.

Still, the men keep hunting this way because they get another (more evolutionary relevant) advantage. They show that they can mobilize the resources to undertake such a costly and dangerous task, which shows they can provide for their offspring, potentially making them more attractive to mates. This behavior is known as “costly signaling behavior,” and the Meriam males use it to gain social standing. The team reports that the turtle hunters get married earlier, to “higher quality” mates, and generally have more surviving children than their peers.

With the advent of social media, these hunters have more opportunity to brag — but they’re also opening themselves to shaming by critics. Public outcry, the team points out, may be a key tactic to stemming such behavior.

“If these hunters are hunting for status essentially, there’s nothing like shame to erode status,” Darimont said.

“So where the internet might fuel this kill-and-tell generation, it might also provide a vehicle for those opposed to trophy hunting to emerge with a powerful strategy.”

The full paper “Why men trophy hunt” has been published in the journal Biology Letters.

Unlikely cooperation: Coyote and badger spotted hunting together

Recent sightings in the area of the National Black-footed Ferret Conservation Center have revealed an unusual partnership: that between a badger and a coyote, successfully hunting together.

Coyote and badger at Black-footed Ferret Conservation Center. Kimberly Fraser, USFWS

Inter-species collaboration is uncommon in the animal world, and even when it does show up, it’s usually between prey animals, not predators. But this is not the first time a badger and a coyote have been observed working together. The two complement each other very well, with the coyote chasing down the prey if it runs away, and the badger digging after it if it goes into a hole.

When they try to hunt alone, they can be either outran or out-burrowed, but together, they are faster and more efficient than any prey. However, these partnerships are rare in colder months. Usually, they happen only during the summer, because in the winter the badger simply digs and finds hibernating animals — it has no need for the fast coyote. In fact, this is quite an open relationship between them, because the two have also been spotted hunting individually sometimes.

Coyote and badger at Black-footed Ferret Conservation Center. Kimberly Fraser, USFWS

A study published in 1992 also concluded that not only is the tandem more efficient when working together, but it also spends less energy and doesn’t have to move as much in the search of prey.

“Complementary morphological adaptations and predatory strategies, interspecific tolerance, and behavioral flexibility allowed them to form temporary hunting associations,” the study writes.

Well, each animal is a remarkable predator in its own right, but together — they’re almost unstoppable.

Why don’t they just eat all of them – predator-prey study reveals new law governing ecosystems

The results of a new study offer insight into the workings of predator-prey mechanisms, more specifically how the number of herbivores and other animals that are preyed upon affect the number of carnivores.

Image via animalslook

McGill PhD student Ian Hatton, lead scientist of the paper, was on vacation when the idea of the study came to him:

“I went to high school in Zimbabwe and spent vacations in the National parks there,” he said. “When I began my PhD in biology at McGill, I wanted to go back and compare whole communities of African animals across protected ecosystems to see how the numbers of carnivores are related to their herbivore prey at the scale of whole landscapes. So I gathered all the animal census data I could for parks in east and southern Africa.”

The wildlife parks of Africa are teeming with tasty, tasty herbivores. So why aren’t there more lions, or more hyenas, to take advantage of the easy feast? One might imagine that the population of predators in each park would increase to match the available prey.

When Hatton and his colleagues started compiling the data and crunching the numbers, summing up all the carnivores (lion, hyena, leopard, etc.) and herbivores (buffalo, zebra, impala, etc.) in these parks, they found a very unexpected and regular pattern.

For every park they looked at, there seemed to be a very consistent relationship of predator to prey, but not in the one they might have expected to find.

Too crowded for romance

What the team discovered was that, across the board, prey reproduced less in crowded settings than they did when their numbers were smaller. They found this same pattern to be consistent with a whole range of different ecosystems. The team believe this to be the bottleneck that keeps predator populations in check ecosystem-wide.

Growth of the predator population seems to be kept in check by the rate of “food” reproduction in any given ecosystem. Image via eurasiareview

“Until now, the assumption has been that when there is a lot more prey, you’d expect correspondingly more predators,” said Hatton. “But as we looked at the numbers, we discovered instead, that in the lushest ecosystems, no matter where they are in the world, the ratio of predators to their prey is greatly reduced. This is because with greater crowding, prey species have fewer offspring for every individual. In effect, the prey’s rates of reproduction are limited, which limits the abundance of predators.”

It’s a surprising find, suggesting a level of structure and function in ecosystems that had not previously been recognized. Although biologists have long made use of very regular mathematical laws -governing functions in the body like metabolism and growth- to explain many of life’s processes, no study has ever shown that similar kinds of laws may exist at a global level. Some scientists are already suggesting that it may well be the discovery of a new law of nature.

Once they observed this pattern in one setting, the team began analyzing data about food pyramids, and the relationship between predators and prey in ecosystems from the Indian Ocean, the Canadian Arctic to the tropical rainforests. Over the course of the next few years they analyzed data gathered about both plants and animals from more than 1000 studies done over the past 50 years covering a range of grassland, lake, forest and ocean ecosystems around the world.

In all these different settings, they found a consistent relation between predators and prey, and confirmation that rather than the numbers of predators increasing to match the available prey, predator populations are limited by the rate at which prey reproduce.

“We kept being astonished,” said Kevin McCann, of Guelph University’s Department of Integrated Biology, one of the study’s co-authors. “This is just an amazing pattern.”

Probably not the kind of predators the study deals with. Probably.
Image via storiesbywilliam

Same rules, different sizes

 

What the researchers also found intriguing was that the growth patterns that govern whole ecosystems, where large numbers of prey seemed to naturally inhibit reproduction, were very similar to the patterns of growth in individuals.

“Physiologists have long known that the speed of growth declines with size,” said co-author Jonathan Davies from McGill’s Dept. of Biology. “The cells in an elephant grow more than 100 times more slowly than those of a mouse.”

“The discovery of ecosystem-level scaling laws is particularly exciting,” added co-author Michel Loreau, adjunct professor in McGill’s Biology Dept. and currently at the Centre national de recherché scientifique (CNRS) in France. “Their most intriguing aspect is that they recur across levels of organization, from individuals to ecosystems, and yet ecosystem-level scaling laws cannot be explained by their individual-level counterparts. It seems that some basic processes reemerge across levels of organization, but we do not yet fully understand which ones and why.”

 

Article suggests dragonflies are the most effective predators in the animal world – 95% success rate

Lions roar and act tough, and they’re often regarded as kind of the land, but only 1 in 4 of their hunts is successful. Sharks have been on top of the food chain for hundreds of millions of years, and still half of their attempts fail. Dragonflies on the other hand, look soft and fragile, and are among the few insects which people generally believe look nice – but they are voracious predators, and may very well be the most efficient hunters in the animal kingdom.

dragonfly2

They snatch their prey mid air with shocking precision, often wolfishly consuming the fresh meat on the spur without bothering to alight.

“They’ll tear up the prey and mash it into a glob, munch, munch, munch,” said Michael L. May, an emeritus professor of entomology at Rutgers. “It almost looks like a wad of snuff in the mouth before they swallow it.”

What does a dragonfly do after it eats? Usually, goes to eat some more – their appetite is just bottomless apparently. Stacey Combes, who studies the biomechanics of dragonfly flight at Harvard, once watched a laboratory dragonfly eat 30 flies in a row.

“It would have happily kept eating,” she said, “if there had been more food available.”

dragonfly3

In a series of recent papers, researchers have pinpointed key features of the dragonfly’s brain, eyes and wings that allow it to hunt so much without failing; one team has shown that they have an almost human-like ability for selective attention, being able to focus on a single insect from a swarm, just as a man at a party focuses on his date, ignoring the background buzz.

In other research, researchers have identified a kind of master circuit of 16 neurons that connect the dragonfly’s brain to its flight motor center in the thorax – this neural pathway enabling it to track a moving target, calculate the interception trajectory and subtly adjust its own path as needed in the process. Apprently, they also use old sailor tricks.

As any experienced sea wolf will tell you, if you’re on a boat, and you see another boat moving at an angle relative to you, and as you approach, the angle doesn’t change, the two of you will crash. The dragonfly does the same thing – it moves in closer to its prety, but always seeing it on the same spot on the retina, keeping the angle constant.

“The image of the prey is getting bigger, but if it’s always on the same spot of the retina, the dragonfly will intercept its target,” said Paloma T. Gonzalez-Bellido, an author of the new report who now works at the Marine Biological Laboratory in Woods Hole, Mass.

Entomologists have shown that this isn’t an active type of hunt, but rather an ambush.

“Before I got into this work, I’d assumed it was an active chase, like a lion going after an impala,” Dr. Combes said. “But it’s more like ambush predation. The dragonfly comes from behind and below, and the prey doesn’t know what’s coming.”

The fact that they’re perfectly adapted for flying and hovering also helps them. They’re able to reach speeds of 50 km/h with only three wing beats, dive, fly backward and upside down, and pivot 360 degrees.

“A dragonfly can be missing an entire wing and still capture prey,” Dr. Combes said.

Full study here.

Salamaders show that being different means staying alive

Remember when we were kids and everyone picked on the ones who looked peculiar in a way or another starting from their hair color and ending with their height? Well, whether you were a “victim” or a “predator” find out that there is a reason why some individuals of a species look at least a bit different. It simply makes predators look away.

As the researchers from the University of Tennessee discovered, birds are most likely to attack those salamanders that look like the majority. The scientists wanted to see how Blue Jays would react facing the prevalence of a dorsal stripe among a group of salamanders.

The discovery is quite intriguing as usually throughout a species’ evolution those traits that make an individual stronger, more able to find food or escape predators are the ones to “survive” while the other ones disappear. As an example those giraffes who had a longer neck were more likely to breed so that in the end the entire species possesses this trait.

However, in this case it seems that being different might keep predators away, thus allowing the individual to survive and breed. The regular back pattern of the salamanders makes them similar to the environment they live in, which makes them hard to see. The striped salamanders released by the researchers in the first day outnumbered the unstriped by nine to one or the other way around. On test days the numbers were evened out but the Blue Jays proved to prefer to attack those models that had seen most before that day. The birds were used to concentrate in order to spot a salamander on the forest floor, this constant effort making them not even notice the ones who were not striped.

So, it seems that the experiment proves a new theory: predators seem to avoid those individuals who look peculiar. Too bad it does not work for bullies too!

source:BioMed Central

Sharks in peril: the world’s fiercest predators cornered, almost extinct

sharkA long time ago, sharks had no natural enemy; they were on top of the trophic chain. All this has changed when man entered the chain, and suddenly (in geological terms) there was no animal safe; some were forced into extinction, many more were threatened, and all feared dire days.

Although this may sound a bit metaphorical and even a bit exagerated, you’d be surprised to see how close to the truth that sentence was. I don’t know about you, but my heart just keeps getting smaller and smaller with each news about a species which is almost extinct; and when even the mighty shark, which symbolizes survival, adaptability, practically invincibility is threatened, you just don’t know where this is going to stop. The fact is that sharks are dissapearing from the world’s oceans; and for what ?! The numbers of many large shark species have declined by more than half due to increased demand for shark fins and meat, recreational shark fisheries, as well as tuna and swordfish fisheries, where millions of sharks are taken as bycatch each year.

“As a result of high and mostly unrestricted fishing pressure, many sharks are now considered to be at risk of extinction,” explained Julia Baum, a member of the IUCN‘s Shark Specialist Group who will be speaking at the American Association for the Advancement of Science Annual Conference in Boston on February 17.

“Of particular concern is the scalloped hammerhead shark, an iconic coastal species, which will be listed on the 2008 IUCN Red List as globally ‘endangered’ due to overfishing and high demand for its valuable fins in the shark fin trade,” added Baum, who is an NSERC Postdoctoral Fellow at Scripps Institution of Oceanography

shark finningAs weird as this may seem, fishing for sharks in international waters is unrestricted! How could things be any good this way? Many people (although it’s hard to call them this way) shark finning (the practice of removing only a shark’s fins and dumping the still live but now helpless shark into the ocean to die) is something of upmost cruelty, and this has to stop! It is estimated that 100 million sharks annually are killed for their fins alone. What would happen if in some country human soup becomes a delicacy? Would the world turn away its head? Without it, the shark just goes to the bottom of the ocean where it dies. Such a dreadful death for such a magnificent creature… to think that when their body hits the water again that they will be safe, only to realize that they can no longer swim, and end up dying in an ocean, which was just moments earlier their safe haven, and is now their doom. This has to be stopped! Here’s a list of things you can do, if you want to get even a bit involved.