Fishers vs Canada lynx

Between 1999 and 2011, researchers in northern Maine radio-collared eighty-five Canada lynx and documented sixty-five deaths. Predation was the leading cause. Fourteen of those kills were attributed to fishers. You read that right, an animal that can weigh as little as eight pounds killing a cat that can weigh over twenty-five, the same cat that we recently wrote about killing mountain goats. It was the first time fisher predation on lynx had ever been documented anywhere in the world. It was not a fluke. It was a pattern.

The study was led by Scott McLellan, assistant regional wildlife biologist with the Maine Department of Inland Fisheries and Wildlife, and published in the Journal of Wildlife Management in 2018. The research began as a status assessment of Maine's lynx population, a federally threatened species whose numbers in the Lower 48 were not well understood. Nobody expected the primary finding to be that the leading predator of the lynx was a mustelid most people could not pick out of a lineup.

A fisher is not a small animal. A large male can weigh thirteen pounds and stretch over three feet from nose to tail. It is the second largest weasel in North America after the wolverine. But a Canada lynx weighs eighteen to thirty pounds, stands taller, has longer legs, and is built to run down snowshoe hares through powder snow. The size gap is real. The lynx should dominate every encounter.

In the forests of northern Maine, the opposite happened fourteen times in twelve years.

The researchers never witnessed an attack. They reconstructed them from the evidence. When a radio collar sent a mortality signal, the team tracked it to the location and worked the scene the way a forensic investigator works a homicide. They searched for the body, examined the neck and skull for bite marks, measured the intercanine width of the punctures to identify the predator, and read the tracks in the snow to determine what had happened before the kill.

The snow told the story every time. Fisher tracks connected with lynx tracks. The fisher had picked up the cat's trail and followed it. In multiple cases, the tracks led directly to a lynx bed where the cat had been lying down, resting or waiting out a snow squall. The fisher attacked the neck and held on.

McLellan told National Geographic: they just buckle on. Drag marks led away from the kill site to a cache location where the fisher had stored the body for later feeding. In one case, a fisher was found inside a tree cavity with lynx remains. In another, a radio-collared female and her uncollared kitten were both found cached at the same site. The fisher had killed the mother and the kitten.

In some attacks, the trauma to the neck was so extensive that researchers could not obtain accurate intercanine measurements because of the amount of repeated biting. The fisher had not delivered a single killing bite and walked away. It had stayed on the throat and kept working until there was nothing left to work on.

McLellan called the species a ball of fury. He said a fisher has no boundaries in the size of animal it is willing to attack. He was not overstating it.

The lynx is not the only predator the fisher kills. There are records of fishers killing fox, mink, otters, and raccoons in direct confrontation. Where fisher populations are dense, marten populations collapse because fishers hunt and kill them in the trees and on the ground. Bobcats, which fall in a similar weight range as lynx, are equally vulnerable.

The fisher is not always ambushing out of desperation. It presses confrontations against larger animals and wins the nerve contest because nothing in the weasel family has ever understood the concept of backing down.

McLellan told National Geographic he was unsure whether fishers take on coyotes but said it was possible. If a fisher can get a hold of the neck of an animal, he said, they are willing to hold on.

The hare cycle is the trigger that puts the fisher and the lynx in the same room. Canada lynx are snowshoe hare specialists. When hares are abundant, lynx are well-fed, strong, and operating in deep-snow habitat where fishers are less effective. When the hare population crashes, lynx weaken. Their bone marrow shifts from white and waxy to red and gelatinous, a diagnostic marker of malnutrition. A 2026 study published in Scientific Reports confirmed that when hare populations drop, habitat overlap between lynx and fishers increases. Both species contract into the same remaining cover.

Several of the lynx killed by fishers in the Maine study showed poor body condition at necropsy. A malnourished lynx bedded down in a snow squall is not the same animal as a healthy lynx running hares through powder. The fisher reads the difference in the tracks before it ever reaches the bed.

Fishers are not invulnerable though. Coyotes kill them. Black bears kill them. Great horned owls take juveniles. Wolves have killed fishers caught in the open on frozen lakes. The fisher exists in the middle of the food web, not at the top. But nothing else in the northeastern forest specifically tracks, ambushes, and kills an animal twice its size with the consistency that the fisher brings to lynx.

Not even the wolverine targets a specific larger predator with this kind of consistency. The wolverine is bigger, stronger, and operates on a larger stage, but it does not track lynx to their beds and kill them in their sleep as a matter of routine. The fisher does. If you put a fisher’s aggression and killing style inside a body the size of a wolverine, even wolves might end up on the menu. Luckily, that animal exists only in imagination.

That fourteen lynx in northern Maine were not dealing with imagination.

Source: McLellan et al. (2018), Journal of Wildlife Management. Maine Department of Inland Fisheries and Wildlife. National Geographic, January 2022. Scientific Reports, February 2026. National Trappers Association.

 

Introduced wild pigs linked to fewer invasive plants, while native deer show the opposite pattern

The introduced wild pigs – feral pigs, wild boars, and their mixes – were associated with lower abundance and lower species richness of invasive plants in forest understories. In contrast, native white-tailed deer were associated with reduced abundance of native tree seedlings, although their effects on seedling richness were more complex.

The study has just been published in Proceedings of the Royal Society B and was led by Ming Ni, at the time a postdoctoral researcher at the Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at Aarhus Universitet.

“We need to move beyond the idea that animals and forests are automatically maladapted to each other simply because they do not share the same origin. Our findings support the idea that ecological impact cannot be predicted from origin alone; feeding behavior, functional traits and environmental context also matter greatly,” says Ming Ni.

Selective deer and omnivorous pigs

The study is based on analyses of more than 68,000 forest plots (for deer; hereof more than 32,000 plots for pigs) across the eastern United States, combined with data from Snapshot USA 2021, the largest annual national mammal camera-trap survey in the United States to date.

The extensive dataset reveals how two major herbivores – the native white-tailed deer and the introduced wild pig – shape forests in very different ways.

Deer are selective feeders. They prefer foliage and seedlings of certain species, while wild pigs forage differently. As omnivores, they root through the soil in search of roots, plants and other food sources.

The animals’ contrasting behaviors are clearly reflected in the vegetation: areas with many deer contained more invasive plants and greater invasive plant diversity, while areas with many wild pigs generally had fewer invasive species.

According to Ming Ni, one possible explanation is that pigs’ rooting behavior and broad diet may disadvantage some invasive plants, but this mechanism requires further testing.

“Our results challenge the widespread assumption that introduced large herbivores are necessarily more harmful than native species. Their ecological impact depends strongly on feeding behavior, functional traits, and the environments they live in,” says Ming Ni.

He also stresses that the effects were highly context dependent. Climate, topography and human influence all played important roles in determining how strongly the animals affected forest understories.

Adding nuance to the debate

In the United States, feral pigs are widely regarded as a major invasive species problem, while in Europe, their native conspecifics wild boars are at the center of intense debates over growing populations, agricultural damage, and disease-management concerns.

Jens-Christian Svenning, senior author of the study and director of ECONOVO, believes the findings are also highly relevant outside the North American context.

“This study shows that we need a more nuanced discussion about biodiversity and ecosystem management. A species’ impact on ecosystems does not mainly depend on whether it is native or non-native, but on what it actually does in nature. That insight is important when discussing the future of forests, biodiversity, and large animals in our present-day human-changed landscapes worldwide,” says Jens-Christian Svenning.

Hereby, the research contributes to the growing international debate about non-native species and their ecological roles. The researchers argue that their results support a nuanced, evidence-based approach to non-native species, recognizing that their roles may span from negative over neutral to positive for resident biodiversity as well as for ecosystem services to society.

 

 

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Journal

Proceedings of the Royal Society B Biological Sciences

DOI

10.1098/rspb.2025.2461 

Snow leopards, leopards and wolves coexist in the same space by choosing different prey

 Large carnivores increasingly coexist in human-modified mountain landscapes, yet empirical evidence on how multiple apex predators partition space, time, and resources to reduce competition remains limited, particularly in the Central Himalaya, Nepal. Understanding these mechanisms is critical for predicting interspecific interactions and informing conservation practices in resource-limited alpine ecosystems. 

This study explored the ecological interactions, competitive dynamics, and coexistence strategies of sympatric snow leopards (Panthera uncia), leopards (Panthera pardus), and Himalayan wolves (Canis lupus chanco) in the Lapchi Valley, Central Himalaya, Nepal. We examined spatial distribution, temporal activity patterns, and dietary overlap among these apex predators using a combination of camera trapping, scat-based DNA analysis, and micro-histological diet assessment. 

The results showed a complete (100%) spatial overlap between the snow leopards and wolves’ ranges. All three predators exhibited predominantly nocturnal activity with strong temporal overlap (0.78). Dietary analyses showed a clear trophic segregation: snow leopards relied mainly on wild ungulates, leopards consumed synanthropic prey, while wolves consumed a mixed diet combining wild and domestic prey. Pianka’s index indicated high dietary overlap between snow leopards and wolves (0.77), but remarkably low overlap of these predators with leopards. The multidimensional niche partitioning appears to reduce direct competition among predators. 

These findings highlight the role of behavioral flexibility, spatial segregation, and prey selection in promoting the coexistence of predators. Conservation strategies must prioritize sustaining wild prey populations, mitigating livestock depredation, and addressing climate-driven habitat shifts that may intensify interspecific competition.

Complete report

The polar bear ‘umbrella’: How protecting one species saves many

 

 To protect the vulnerable biodiversity of the Arctic, researchers from the University of Alberta and San Diego Zoo Wildlife Alliance (SDZWA) have identified a new conservation strategy in western Hudson Bay: using polar bears as an "umbrella species" to guide where protection is needed most.

Establishing boundaries for marine protection is often difficult due to a lack of data on where marine life gathers. Polar bears offer a solution: by analyzing two decades of tracking data from 355 bears, a new study in Arctic Science identified a “high-use” area near Cape Churchill, Manitoba, highlighting it as a prime location for a Marine Protected Area (MPA).

According to the study’s authors, including U of A biological sciences professor Dr. Andrew Derocher and Dr. Nicholas Pilfold, conservation scientist at SDZWA, protecting polar bear habitat naturally safeguards the resources they rely on to survive. In turn, polar bears provide critical benefits to the ecosystem; for example, their leftover kills feed scavengers like Arctic foxes, wolves, ravens, and gulls. The research shows polar bears meet nearly all the criteria for an umbrella species, including well-documented biology, vast home ranges, and a high sensitivity to human disturbance.

Last month Manitoba Premier Wab Kinew announced funding to explore the establishment of a national marine conservation area in western Hudson Bay. 

“By leveraging the extensive data we have on polar bears, we can help design MPAs that safeguard both the bears and the vast network of Arctic species that rely on them,” says Dr. Pilfold. “Well-designed dynamic MPAs have the potential to preserve biodiversity in a constantly changing Arctic landscape.”

The authors acknowledge climate change and melting ice may eventually reduce the polar bear’s habitat, but using the northern bear as an umbrella species can provide a good starting point. 

"In the rapidly warming Arctic, marine ecosystems will be stressed by the additive effects of industrial activity and polar bear location data provide a path to designing marine protected areas," says Dr. Derocher.

Ravens don’t follow wolves to dinner – they remember where the food is

 

Summary author: Walter Beckwith

Peer-Reviewed Publication

American Association for the Advancement of Science (AAAS)

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New findings challenge the long-held idea that scavengers seeking food routinely follow predators to find it. Studying common raven, gray wolf, and cougar in Yellowstone National Park, researchers found that ravens rarely trail predators over long distances; instead, they rely on spatial memory to return to places where kills have occurred before. Scavenger species that rely on the kills of predators face the challenge of finding food that is patchily distributed, unpredictable, and often ephemeral because many animals compete for it. A widely accepted hypothesis suggests that scavengers solve this problem by adjusting their movements to follow large carnivores to their kills. Although scavengers are frequently observed near carnivores in the field, it’s unclear whether following behavior reflects the dominant foraging strategy. However, this hypothesis has been difficult to evaluate due to the challenge of simultaneously tracking predators and scavengers across large distances.

 

Matthias-Claudio Loretto and colleagues investigated how common raven locate carrion by studying their interactions with grey wolf and cougar in Yellowstone National Park. Ravens are often seen traveling with wolves and rapidly gathering at fresh kills. Loretto and colleagues hypothesized ravens may rely on memory and prediction to revisit areas where predators frequently make kills, rather than following them in real time. Loretto et al. used GPS devices to track the movements of ravens, wolves, and cougars over 2.5 years, as well as records of hundreds of wolf and cougar kills. Contrary to longstanding assumptions, the authors found that long-distance predator following was rare. Instead, ravens repeatedly returned, sometimes from distances of up to 155 kilometers, to areas where wolf kills were common. Raven-cougar interactions were rare. The findings indicate that ravens rely on spatial memory, treating areas with historically high kill density as predictable foraging sites. According to the authors, this suggests that navigation and memory, rather than real-time tracking of predators, play the dominant role in how ravens locate food sources.

 

Podcast: A segment of Science's weekly podcast with Matthias-Claudio Loretto, related to this research, will be available on the Science.org podcast landing page after the embargo lifts. Reporters are free to make use of the segments for broadcast purposes and/or quote from them – with appropriate attribution (i.e., cite "Science podcast"). Please note that the file itself should not be posted to any other Web site.

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Journal

Science

DOI

10.1126/science.adz9467 

Why do female caribou have antlers?

Biologists have long wondered why caribou are the only deer in the world in which females, like males, have antlers.

A study of shed antlers collected from calving grounds in the Arctic National Wildlife Refuge provides a new answer.

Calving grounds are areas where migratory females give birth every year and also where they shed their antlers. Researchers at the University of Cincinnati found evidence that caribou, particularly moms with newborns, gnaw on antlers that were shed years earlier to supplement their diets with crucial minerals.

The study was published in the journal Ecology and Evolution.

Associate Professor Joshua Miller and doctoral graduate Madison Gaetano at the University of Cincinnati studied antlers collected from the Arctic National Wildlife Refuge of Alaska, home to the Porcupine Caribou Herd, which is famous for its epic 1,500-mile round-trip migration.

Antlers are made of bone that grows from the top of the skull The antlers of male caribou can stretch four feet and weigh as much as 20 pounds each, although a female’s are far smaller.

In the cold and dry climate of the Arctic tundra, shed antlers can sit undisturbed for hundreds of years, providing a ready source of minerals such as calcium and phosphorus for foraging caribou at a key time of their epic migration.

Miller collected antlers and bones during scientific expeditions to the Arctic Refuge between 2010 and 2018. He used a rigid inflatable raft, setting up camps with a portable electric fence to ward off curious bears. During the expeditions, it was clear that most of the antlers had been chewed on, but which animals were doing the chewing?

Back in Miller’s lab at UC, researchers examined the tooth marks left on the antlers and bones to identify the culprits. When carnivores such as bears and wolves chew on bones, they leave distinct patterns of damage compared to animals such as lemming or caribou.

UC researchers found that caribou are the prime culprits, chewing antlers they find a little at a time starting at the tips of the tines.

The study found that 86% of the 1,567 antlers they examined showed signs of gnawing and 99% of the gnaw marks were left by caribou.

“We knew that animals gnawed on these antlers, but everyone assumed they were mostly rodents. Now we know it’s really caribou. My jaw dropped when our results started to become clear,” he said.

Researchers observed marks from rodent teeth on less than 4% of gnawed antlers. And they found no evidence of carnivore gnaw marks on antlers in the study.

Researchers also collected 224 skeletal bones from caribou, moose and musk ox in the study area. And unlike the antlers, many of the gnaw marks on these bones were from predators such as wolves and  bears. Caribou gnaw marks were observed on about 12% of the sample bones while just 1% of gnaw marks were from rodents.

Patrick Druckenmiller, a professor from the University of Alaska Fairbanks and Director of the University of Alaska Museum of the North, and National Park Service program manager Eric Wald also contributed to the project. The research was supported with grants from the U.S. Fish and Wildlife Service, the National Geographic Society, the National Science Foundation, the UC Office of Research and the Animal Welfare Institute.

Biologists often point to antlers as a tool for females to defend the choicest grazing spots from other caribou or to ward off predators. But Miller said the role shed antlers play in supplementing a caribou’s diet is an overlooked benefit.

Migrating females collectively drop their antlers within days of giving birth. In this way, females carry their own nutritional supplement that becomes available where and when they need it most.

“These antlers last for centuries or longer in the Arctic and they are a source of nutrients that get revisited again and again. Given the results of our study, this is probably an important clue to a way that antlers benefit female caribou that has gone underappreciated,” he said.

Gaetano said antlers certainly could provide more than one benefit to female caribou. But female caribou are more likely to use their hooves against predators. Reindeer herders she spoke to said their go-to defense is to trample and kick. 

Meanwhile, their antlers can be very small, she said, making them unlikely weapons.

“I think it's reasonable to question how helpful they would be in fighting off a predator,” she said.

“Female caribou shed their antlers right around when they give birth,” Gaetano said. “That means they are antlerless when it would be most crucial to have antlers to defend a young calf if they were a defense mechanism.”

Eventually, over the span of centuries, the minerals from the shed antlers return to the soil where the nutrients help support sedges, grasses and lichens the caribou eat.

“They’re engineering this habitat, seeding the landscape with these super-important minerals that can be quite hard for animals to get enough of,” he said. “Phosphorus in particular is very important for new mothers trying to produce high-quality milk for feeding their young. Caribou bring literally tons of phosphorus to their calving grounds every year.”

Miller said many mammals are known to supplement their diet by gnawing bones, eating clay and salt or drinking from mineral-rich pools.

“It is fairly ubiquitous. I’ll never forget watching a kangaroo eat a dead bird in Australia,” he said. “Herbivores look for nutrients in all kinds of interesting ways.”

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Journal

Ecology and Evolution

DOI

10.1002/ece3.72444 

Wolf reduction boosts caribou survival—but only in rugged terrain

 Reducing wolves to protect endangered caribou doesn't always deliver the expected results—and the shape of the land may be the deciding factor.

That’s according to research led by doctoral student Tazarve Gharajehdaghipour and professor Dr. Cole Burton in UBC's faculty of forestry and environmental stewardship, which examined newborn caribou survival in Itcha Ilgachuz Park in west-central B.C.

Using GPS collars to track animals, the team found that B.C. wolf removals boosted calf survival in steep, mountainous terrain, but made no difference in flatter terrain.

"This study is a note of caution," said Dr. Burton. "Different herds face different conditions. Wolf control may not be reducing calf mortality as effectively as we once thought."

How land and predators affect calf survival

The key factor is which predators can catch calves at different ages. Bears and wolverines hunt newborn calves in the first two weeks, but can’t catch older, more mobile calves. Wolves, by contrast, can catch the older, faster calves.

In rugged areas, this makes a big difference. Bears and wolverines can kill newborns at high elevations, but by the time mother-calf pairs move down to valleys at around three weeks old, the calves are too fast to catch. At this stage, wolves become the main threat.

Before wolves were removed, most calf deaths occurred during this period. Removing wolves eliminated this later cause of death, boosting survival by 41 percentage points—because bears and wolverines cannot hunt the older calves effectively.

In more accessible areas, wolves can reach calving sites throughout the season, including early when calves are young and vulnerable. When wolves were removed, other predators, such as bears and wolverines, simply killed more of these young calves, so overall survival did not improve.

Tracking calves through mothers’ movements

This is the first study to use GPS collars to follow newborn mountain caribou survival. The research builds on tracking methods developed by co-author Dr. Marie Auger-Méthé, a UBC associate professor in the Institute for the Oceans and Fisheries and department of statistics.

They found clear patterns: mothers abruptly start moving less when giving birth to stay close to newborns, then gradually increase activity as calves get stronger, or quickly return to normal movement if a calf dies.

"This method lets us watch the critical first four weeks of life, when calves are most at risk. We also used camera traps to see when predators were on the calving grounds," said Gharajehdaghipour.

The caribou collar data, which this research paper is primarily based on, was collected by B.C. government biologists, and secured through open access. 

Conservation beyond predator control

The research also found that calf deaths before wolf reduction—likely caused by wolves—were linked to horseback and ATV trails and treed valleys. This suggests wolves use these areas to reach calves. Limiting trail development could help reduce wolf-caused deaths in places where wolf control isn’t used.

While B.C.'s wolf reduction program now covers 15 caribou herds, Dr. Burton emphasizes it’s critical to protect habitat.

"If wolf control is sometimes ineffective and diverts attention from habitat restoration, it's a real concern," he said. "Without recovering habitat, you'd have to keep controlling wolves indefinitely."

The researchers recommend that wildlife managers consider the landscape, predator communities, and habitat conditions before starting wolf control programs. They also encourage using GPS tracking and camera traps to better understand calf survival across B.C.

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Journal

The Journal of Wildlife Management

DOI

10.1002/jwmg.70143