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Not All Camouflage Is Equal. Here Are Prey Animals' Best Options | Science News

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From crabs to caterpillars, a wide range of animals successfully use camouflage to hamper detection by hungry predators. But some concealment strategies are more effective than others, a new study suggests.

The analysis compiles and synthesizes data from scores of studies on animal camouflage. Comparisons between different camouflaging methods show that masquerading as specific objects in the environment is the best way to go unseen, scientists report September 14 in Proceedings B of the Royal Society

Behavioral and sensory ecologist João Vitor de Alcantara Viana had been studying animal camouflage for his doctoral research when he realized a comprehensive comparison of different camouflage strategies had never been done. 

“There was a big gap in the literature on this topic,” says de Alcantara Viana, of the State University of Campinas in São Paulo, Brazil.

So, de Alcantara Viana and colleagues searched scientific publication databases for studies on animal camouflage dated from 1900 through July 2022. The team zeroed in on 84 studies that experimentally tested at least one camouflage strategy, and reported either how long predators took to find camouflaged prey or how often predators attacked. The team also limited their analysis to studies that compared camouflaged prey with noncamouflaged, often artificial, versions.

Next, the team grouped the data from these studies by the types of predators and prey analyzed and the variety of camouflage strategies examined. Camouflage tactics included “background matching,” where the animal matches the color and patterning of the environment, and “masquerading,” where prey mimics a particular object uninteresting to predators, like a twig, a leaf, a bird dropping or even a shed tarantula skin (SN: 12/10/13; SN: 6/6/14).

Camouflage is generally effective at making the hunt difficult for predators, increasing their search time by more than 62 percent and dropping the rate they attack prey by more than 27 percent across the board, the team found. 

But the type of prey mattered. Caterpillars got more benefit from camouflage than their winged adult forms, for example. This may be because moths and butterflies can fly and have other antipredator adaptations available to them, de Alcantara Viana says.

The masquerade strategy was especially effective at helping prey elude predators, increasing search time by nearly 300 percent. One of the most striking examples of this, says de Alcantara Viana, are caterpillars that disguise themselves as twigs. A study on brimstone moth caterpillars (Opisthograptis luteolata) and chickens showed that the birds take longer to attack masquerading caterpillars after being recently exposed to twigs. 

Masquerading as the most effective camouflage strategy is intriguing, says Anna Hughes, a sensory ecologist at the University of Essex in England who was not involved with this research. “If this is indeed the case, it will be interesting to further investigate the constraints — size, movement requirements — that mean that not all animals evolve this strategy,” she says. The researchers note that masquerading is probably more likely to evolve if the animal is a similar size as the object it’s mimicking. This could limit what species can benefit from this super camo.

de Alcantara Viana and his colleagues think masquerading is so effective because it’s so specialized, with animals impersonating specific objects, compared with other strategies based on blending in against an irregular background. Prey that masquerade benefit from the predator misidentifying them as real objects in the environment, not just failing to detect the prey. 

The quality of the new work is excellent, Hughes says. Still, it’s not quite clear if the noncamouflaged controls, which she says vary quite widely from one study to another, have inherently different effects on predator reactions. This could make the tested camouflage seem more or less effective than it is in nature.

Another notable finding from the new analysis is that most studies have been conducted in the Northern Hemisphere, Hughes says. “I think it is clear that our understanding of the evolution of camouflage strategies is going to be, by definition, incomplete unless more studies are carried out in the Southern Hemisphere.”

Much of recent camouflage research has also tried to understand precisely how specific defenses protect prey from attacks, says Tom Sherratt, an evolutionary ecologist at Carleton University in Ottawa, Canada, also not involved with this study.

“We are now at a point where we can begin to compare among these defenses,” Sherratt says, which can help researchers figure out why species use particular camouflage strategies.

de Alcantara Viana says he and his colleagues are working on another analysis to understand “the other side of the coin,” how camouflaged predators benefit from concealing themselves from prey.

Animals

Mountain Lions Pushed Out By Wildfires Take More Risks

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Mountain lions have no interest in people, or the built-up areas we enjoy. But after a 2018 wildfire in California, local lions took more risks, crossing roads more often and moving around more in the daytime, scientists report October 20 in Current Biology. It’s another way the effects of human development could be putting pressure on vulnerable wildlife — in this case, potentially pushing them toward our bumpers.

The Woolsey Fire began near Los Angeles on November 8, 2018, and burned more than 36,000 hectares in the Santa Monica Mountains. Nearly 300,000 people evacuated, and three people died. Animals fled the fire too, including the local mountain lions (Puma concolor). The fire was a tragedy, but also a scientific opportunity, says Rachel Blakey, a global change biologist at UCLA. Many of the lions wore tracking collars, allowing scientists to study how the fire changed their behavior.

Of the 11 collared cougars in the area at the time, nine made it to safety during the fire itself. “They have really large home ranges, so it’s nothing to them to be able to cover many kilometers in a day,” Blakey says.

No matter how much they moved, the mountain lions avoided people. One collared cat, P-64, initially fled the fire — until he got close to a developed area. Given the choice between fire and people, the lion retreated back into the burning area. “That’s where his movements stopped,” Blakey says. The park service later found P-64’s remains. He’d burned his paws, and it’s possible that he was unable to hunt and starved to death.

Using data from the nine lions that survived the fire and others collared after, the scientists showed that the cats generally avoided the severely burned areas of their territories. With vegetation gone, the cats had little cover for stalking and ambushing prey.

Instead, the cougars stuck to unburned areas, and continued to avoid people. But they took more risks around human infrastructure, increasing their road crossings from an average of about three times per month to five.

A mountain lion seen running across a paved road, away from the camera
After the Woolsey Fire in 2018, mountain lions in the Santa Monica Mountains crossed roads more often, a risky move that could put the cats’ lives in danger.National Park Service

These weren’t all two-lane country highways. The first collared lion to successfully cross Interstate 405, which has 10 lanes in places, did it after the Woolsey Fire. And the big cats crossed U.S. Route 101 once every four months, whereas before the fire, they’d crossed only once every two years. Their territories also overlapped more often, increasing the potential for deadly encounters between the solitary cats. And the generally nocturnal animals increased activity during daytime hours from 10 percent to 16 percent of their active time — boosting a lion’s chances of potentially bump into a human.

Road crossing is what Blakey calls a “risk mismatch.” Lions in areas with lots of people appear to weigh the risk of encountering humans as more dangerous. But “running across a freeway is a lot more likely to be fatal,” she says. That risk, combined with the risk of running into other cats, can be deadly. One young, collared male ended up dead on a freeway in the months after the fire. He was fleeing a fight with an older, uncollared male.   

Intense burns like the Woolsey Fire highlight the resilience of mountain lions, says Winston Vickers, a wildlife research veterinarian at the University of California, Davis who was not involved in the study. “They have amazing mobility, they mostly can get away from the immediate fire, they mostly survive,” he notes. The changes in risk-taking, he says, could reflect how confined the population is, hemmed into the mountains by human development.

Wildlife crossings, such as the new Wallis Annenberg Wildlife Crossing over the 101, will hopefully give the mountain lions a safer option for roaming, though the main goal is to promote gene flow between lion populations, Blakey says (SN: 5/31/16). In a landscape where fire, humans and highways combine, it’s good to have somewhere to run.  

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A Parasite Makes Wolves More Likely To Become Pack Leaders

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A parasite might be driving some wolves to lead or go solo.

Wolves in Yellowstone National Park infected with Toxoplasma gondii make more daring decisions than their uninfected counterparts, researchers report November 24 in Communications Biology. The wolves’ enhanced risk-taking means they are more likely to leave their pack, or become leaders of their own.

“Those are two decisions that can really benefit wolves, or could cause wolves to die,” says Connor Meyer, a field biologist at the University of Montana in Missoula. The findings reveal a parasite’s potent ability to influence a wolf’s social fate.

Disease is often considered important for wildlife, mostly in the context of killing its host, Meyer says. “We have evidence now that just being infected with a certain parasite — Toxoplasma — can have pretty major implications for wolf behavior.”

A microscope image of the Toxoplasma gondii parasite
The single-celled parasite Toxoplasma gondii is known to alter the behavior of its warm-blooded animal hosts in ways that help complete the microbe’s life cycle.Todorean Gabriel/iStock/Getty

Single-celled T. gondii has a track record of altering animal behavior. Its most important hosts are cats, which provide a breeding ground for the parasite in their small intestine. The parasite offspring hitch a ride on feline feces. Other animals then ingest the parasite, which then manipulates its new hosts’ behavior by tweaking certain hormones, making the hosts bolder or more aggressive. Infected mice, for example, can fatally lose their fear of cats, allowing the parasite to infect more hosts once the mice are consumed (SN: 1/14/20). 

In Yellowstone National Park, many wolves are also infected with T. gondii, recent research has shown. So Meyer and colleagues wondered if gray wolves (Canis lupus) in the park showed any parasite mind-bending of their own.

Wolves were reintroduced to Yellowstone in 1995. Ongoing study of the park’s packs meant that the researchers had access to about 26 years’ worth of blood samples, behavioral observations and movement data for 229 of the park’s wolves.

The team screened the wolf blood for antibodies against T. gondii parasites, which reveal an infection. The researchers also noted which wolves left their pack — usually a family unit consisting of a breeding pair and their offspring — or became a pack leader. 

Both are high-stakes moves for a wolf, Meyer says. 

Infected wolves were 11 times as likely as noninfected wolves to disperse from their pack, the team found, and about 46 times as likely to eventually become leaders. The findings fit in with T. gondii’s apparent ability to boost boldness across a wide range of warm-blooded life. 

The study fills a crucial gap in the Toxoplasma pool of knowledge, says Ajai Vyas, a neurobiologist at Nanyang Technological University in Singapore, who was not involved with the study.

“Most of the earlier work has been done in the lab,” Vyas says. But there are limitations to that approach, especially for re-creating how animals experience the effects of the parasite in their natural environment. Such research has “become almost like studying whale swimming behavior in backyard pools; [it] does not work very well.”

Wolves’ enhanced boldness may even form a feedback loop, the team proposes. The researchers found that not only do cougars (Puma concolor) in the park carry the parasite, but wolves’ infection rates were highest when the animals’ ranges overlapped with the park’s densest aggregations of cougars. Infected wolf leaders may be more likely to bring pack members into riskier situations, including approaching cougar territories, making additional infections more likely. 

The feedback-loop idea is “very fascinating,” but more research is needed to confirm it, says Greg Milne, an epidemiologist at the Royal Veterinary College in London, who was not involved with the study. Such research may involve determining if infected wolves are more likely to migrate into an area with more cougars. 

“I think people are just starting to really appreciate that personality differences in animals are a major consideration in behavior,” says study coauthor Kira Cassidy, a wildlife biologist at the Yellowstone Wolf Project in Bozeman, Mont. “Now we add a parasite-impacting behavior to the list.”

Next, the team is interested in examining the long-term consequences of a T. gondii infection, and whether infected wolves make better leaders or dispersers than uninfected wolves.

 It’s also not known how infection impacts survival and reproduction rates, Cassidy says. “Infection may very well be detrimental in some ways and advantageous in others.”

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A New Book Asks: What Makes Humans Call Some Animals Pests?

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Pests
Bethany Brookshire
Ecco, $28.99

We spend so much time making sure wildlife stays away from us, whether that’s setting traps, building fences or putting out poisons. Sure, unwanted guests are annoying. But why do we consider some animals “pests”? It’s all about perspective, says science journalist Bethany Brookshire. “We can put poison out for rats and protest their use as laboratory animals. We can shoot deer in the fall and show their adorable offspring to our children in the spring,” she writes in her new book, Pests: How Humans Create Animal Villains.

Brookshire argues that we deem animals “pests” when we fear them (like snakes). Or when they thrive in a niche we unintentionally created for them (think rats in the New York subway). Or when they find a way to live in a habitat now dominated by humans (all those deer in the suburbs). Sometimes we demonize an animal if we feel like it’s threatening our ability to control the landscape (like coyotes that attack our livestock, pets and even children).

Through the lens of science, history, culture, religion, personal anecdotes and a big dose of humor, Brookshire breaks down how our perspective shapes our relationships with our animal neighbors. She also goes into the field — trailing rats, hunting pythons, taming feral cats, tracking drugged-up bears — to see firsthand how pests are treated.

Science News spoke with Brookshire, a former staff writer for Science News for Students (now Science News Explores), about what we can learn from pests and how we can co­exist with them. The following conversation has been edited for clarity and brevity.

SN: What inspired you to write this book?

Brookshire: I wrote a news story that was about mice living with humans (SN: 4/19/17). [It was based on a study] showing that we’ve had house mice since we’ve had houses. I love the fact that humans have had these other animals taking advantage of the ecosystems that we create basically since we started living settled life. Every location that has humans has their “rat.” Sometimes that’s a rat, and sometimes it’s a pigeon or a cockatoo or a lizard or a horse. It’s not about what these animals are doing. Animals live in ecosystems that we create, and we hate animals that live too close.

SN: What surprised you during your research?

Brookshire: The reflexiveness of people’s responses [to pests]. People respond emotionally. When you make them pause and think about it, they go, “Oh wow, that doesn’t make any sense. I should not be caught trying to kill a raccoon with a sword.” But in the moment, you’re so wrapped up in the violation of what you see as your personal space.

The other thing is the extent to which our disdain of pests is wrapped up in social justice. A lot of times we see this hatred and disgust for animals that we see as “low class.” High-class people don’t have rats. And that’s really about social justice, about infrastructure and the ability of people to live in clean houses, store their food properly or even have a house at all.

Also, the way we deal with these animals often has vestiges of colonialism, as in the chapter on elephants. [In Kenya, European colonists] made people grow corn and sugarcane, which elephants love. Colonization created national park systems that assumed that humans had no place in wilderness, shoving out Indigenous pastoralists. Colonization created the market for poached ivory. And colonizing people assumed that Indigenous people did not like elephants or know their benefits. We are living with the consequences. Many modern efforts at elephant protection are spearheaded by Western people, and they assume the biggest issue with elephants is poaching and that Indigenous people don’t know what’s best for themselves or the elephants. In fact, human-elephant conflict [which includes elephant crop raids] is the far bigger problem, and Indigenous people have a long history of coexisting with elephants.

SN: In the book, you looked at many different cultures and included Indigenous voices.

Brookshire: It’s important to realize there’s more than one way to look at the world. By learning from other cultures, it helps us understand our biases. It’s only when you get outside of your own beliefs that you realize that’s not just the way things are.

SN: That shows up when you write about the Karni Mata Temple in India, also known as the Temple of Rats. Temple rats are not treated as pests, but a rat in a house would be.

Several rats sitting on the rim of a bowl of milk sitting on the ground
India’s Karni Mata Temple is home to thousands of black rats, which devotees believe are people reincarnated as rats by the goddess Karni Mata. The rats are given meals and milk in large bowls. In other contexts, rats are usually unwelcome visitors.Credit: Günther Jontes/Wikimedia Commons (CC BY 4.0)

Brookshire: That’s the result of context. And you see that in Western cultures all the time. People love squirrels. Well, they’re basically rats with better PR. Then you have people who have pet rats, who would probably scream if a sewer rat ran by.

SN: Are there any animals that you consider a pest?

Brookshire: No. The animal that I’ve probably come away with the most negative impression of is humans. It’s funny because we think we can extinct anything. And I love how these animals have gone: “Oh, poison? That’s cute.” “Oh, a trap? You’re funny.” We’ve tried to use electric fences on elephants [to stop them from eating crops]. And elephants are like, “Guess what? Ivory doesn’t conduct electricity.” Even if they don’t have tusks, elephants just pick up a log [to destroy the fence].

SN: Are you hoping to change people’s minds about pests?

Brookshire: I hope that they will ask why they respond to pests the way they do. Instead of just going, “This animal bothers me,” ask why, and does it make sense. I also hope it opens more curiosity about the animals around us. I learned from Indigenous groups just how much knowledge they have of the animals in their ecosystem. I hope more people learn. A world that you know a lot about is just a better world to live in.


Buy Pests from Bookshop.org. Science News is a Bookshop.org affiliate and will earn a commission on purchases made from links in this article.

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