Beavers thrive in river estuaries along North America’s northwest coast

 

High-density beaver dams may have important ecological role beyond their traditional habitat

Peer-Reviewed Publication

PLOS

FacebookXLinkedInWeChatBlueskyMessageWhatsAppEmail

 

image: 

Beaver dam and pond in the Snohomish Estuary’s Quilceda marsh (48.05° N, 122.19° W). Note shrubs and spruce trees in background, tidal sedge (Carex lyngbyei) in the foreground. A log has drifted in on a higher high tide and has come to rest on the side of the beaver dam. The pond is waist to chest deep with an accumulation of soft, unconsolidated sediments. During higher high tides water reaches the marsh surface. Photo by the author (Figure S1).

view more 

Credit: W. Gregory Hood., 2026, PLOS One, CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

Beavers are widespread in estuaries and tidal wetlands in the Pacific Northwest of the United States, demonstrating that they are not restricted to rivers and streams, Gregory Hood at the Skagit River System Cooperative, USA, reports on July 8, 2026 in the open access journal PLOS One.

Beavers are famous for their construction skills, building domed lodges and damming rivers with logs. The ponds that their dams create can provide important habitat for plants, birds and fish, and their ability to alter ecosystems has given them the title of ‘ecosystem engineers’. Beavers can also be found in estuaries, where the twice-daily ebb of the tides causes water fluctuations and brings in saltwater from the ocean. However, little is known about beaver ecology and behavior in these tidal habitats.

Researchers surveyed North American beaver (Castor canadensis) lodges and dams in tidal wetlands in British Columbia, Washington, and Oregon to understand how beavers use river deltas and estuaries. They found that beavers were widespread in these tidal habitats, with an average of 19 dams and 2 lodges per kilometre in surveyed channels of the Snohom­ish and Skagit rivers. This is more than twice the density of beaver dams that has been previously reported for non-tidal river channels. Detailed measurements of beaver structures revealed that dams in tidal habitats tend to be shorter than those in rivers, meaning that they would usually be flooded at high tide. This suggests that their main function is to trap water at low tides, allowing beavers to move freely through the river system. They may also help to block saltwater brought in by the tide. The researchers inspected historic aerial photos on Google Earth dating back to 1990 and found that an estuarine beaver dam can remain in place for at least 35 years, spanning multiple generations of beaver.

The study expands the known habitat distribution of beavers and demonstrates that these charismatic creatures can thrive in river estuaries. The density of dams also suggests that they may have a significant ecological impact in these habitats. By creating deep pools of water at low tide, their dams may provide important habitat for threatened species, such as Chinook and coho salmon. But more research is needed to understand how conservationists can work with beavers to restore river estuaries in the Pacific Northwest, the authors say.

The author adds: “The conventional view of beaver is that they live exclusively in rivers and lakes. My work shows that beaver are much more adaptable than this. They are also broadly distributed and resident in tidal marshes and swamps of the Pacific Northwest, from at least British Columbia to southern Oregon. So, it would not be surprising if beaver were found in tidal habitats in other regions of North America or Eurasia.”

 “Now that we know that beaver can be commonly found in tidal wetlands, we also know that there are new questions to ask about beaver ecology in these systems. We have a lot to learn about tidal beaver ecology and how it compares to more conventional river and lake beaver.”

“Knowing that beaver are commonly found in tidal marshes and swamps leads to the realization that we need to account for the ecosystem effects of beaver in these systems. Beaver are ecosystem engineers in rivers and lakes, i.e., their dam-building activities have broad effects on other flora and fauna in those ecosystems. So, they are likely to also be ecosystem engineers in tidal ecosystems. Without accounting for beaver in tidal ecosystems our understanding and management of these systems is likely to be incomplete and flawed.”

 The freely available article in PLOS One: https://plos.io/3R9H1Xp

California wolves feed heavily on cattle

Two new studies examining gray wolves in California paint a complex picture of life on California’s ranching landscapes: wolves eat cattle more than anything else and the presence of the predators causes significant stress among livestock.

In the first study, University of California, Davis, researchers found wolves from the Lassen and Harvey packs in northeastern California were primarily eating cattle. They collected scat samples during the summer months of 2022 and 2023 and found 72% of wolf scat contained cattle DNA. The research was published in PLOS One.

“Whether it's through scavenging or whether it's through depredation, it’s a huge component of the wolves’ diet,” said lead author Tina Saitone, a professor of Cooperative Extension in the UC Davis Agricultural and Resource Economics Department. “Their conservation success is because of livestock producers in the state.”

Cattle appeared as the most frequently occurring food item during both summers of the study, present in 86% of samples in 2022 and 55% in 2023. While all 2022 samples were from the Lassen Pack, the 2023 samples included eight from the newly established Harvey Pack. 

Wolves are a state and federally recognized endangered species. The first confirmed wolf entered California in 2011, following a nearly 100-year absence. The California Department of Fish and Wildlife estimates the state is now home to nine wolf packs. 

Few natural prey

Wolves in California live in landscapes shaped by people. They have fewer wild ungulate prey options than wolves in other parts of North America. Mule deer are their only significant wild food source, but populations have dropped sharply since the 1970s. 

Saitone said the scarcity of wild prey may be one reason wolves are eating cattle instead. Researchers found mule deer in just 45% of the scat samples, significantly less common than cattle. 

Keeping wolves away from cattle is difficult on many of these working landscapes. 

“Conservatively, we’re talking about a million acres in our study area and 10,000 cow-calf pairs,” said Saitone. “It’s not as simple as putting up an electric fence on a two-acre pasture or putting cattle in the barn at night.”

Cattle are stressed

Researchers also examined how living among wolves affects cattle. Their findings suggest the costs of wolf reintroduction extend well beyond animals lost to predation.

A second study, published in Ecology and Evolution, measured cortisol levels in tail hair samples collected from beef cattle grazing rangelands in northeastern California — some herds sharing territory with wolf packs, others in areas without wolves. Cortisol, often called the stress hormone, accumulates in hair over time, making it a reliable indicator of chronic stress rather than a momentary response to fright.

Cattle herds living among wolves had cortisol levels 58% higher than those in control herds — a significant physiological difference. This marks one of the first times hair cortisol analysis has been used to study how the reintroduction of predators reshapes livestock physiology in the field.

"What this really confirms is that death or depredation is not the only impact here," said Saitone. "Living among wolves for cattle is a chronically stressful experience, and that could ultimately have production-related impacts in both the short and the long term."

Could it affect reproduction?

Saitone said the findings are just a starting point. Researchers next want to understand whether elevated stress levels translate into lower conception rates. It’s a concern long raised by ranchers that has not yet been established through direct biological evidence. When breeding cows fail to conceive, it can directly affect a rancher’s bottom line.  

"That's their whole purpose,” said Saitone. “These are mother cows that are supposed to be generating calves as a marketable product.” 

Mountain lions have major ecological impact even in small preserve

 

Peer-Reviewed Publication

Stanford University

FacebookXLinkedInWeChatBlueskyMessageWhatsAppEmail

 

image: 

A mountain lion photographed by a motion-activated cameras on Stanford's Jasper Ridge Biological Preserve.

view more 

Credit: Image courtesy of Trevor Hébert/Stanford University.

Big cats have a big impact. A long-term study showed that when mountain lions began regular visits to a small, suburban preserve about 45 miles south of San Francisco, it changed the behavior of many other animals.

Mountain lions (Puma concolor) started appearing with increasing frequency on trail cameras at Stanford’s Jasper Ridge Biological Preserve ('Ootchamin 'Ooyakma) from 2015 to 2020. Researchers documented a corresponding drop in deer activity compared to the prior years of lower or absent puma activity. Vegetation surveys also showed that many woody plants deer like to eat or tend to trample, including young oak trees, began to thrive.

These types of multi-level effects, called trophic cascades, have been studied primarily in large wilderness areas, particularly cascades caused by apex predators such as wolves reintroduced into Yellowstone National Park. This research, published in Ecology and Evolution, indicates the effect can be found in smaller preserves as well.

“In the past, small preserves like Jasper Ridge have often been dismissed for holding very little ecological value, but this study shows that when these small preserves are connected to large wilderness like the Santa Cruz Mountains, you can still see magnificent ecological phenomena like trophic cascades,” said Chinmay Sonawane, the study’s first author and doctoral student in biology in Stanford’s School of Humanities and Sciences (H&S). “They are not just things that happen in places like Yellowstone far away from the city and people. They can happen in these places that are quite small and more urban as well.”

The ecology of fear
The researchers analyzed data frommotion-activated cameras and vegetation surveys and found two types of trophic cascades, one that connected mountain lions, deer, and vegetation, called a tri-trophic cascade, and another that involved smaller predators at Jasper Ridge. For the second, increased puma presence was associated with decreases in the activity of coyotes and bobcats, which were perhaps leaving the area or changing the time they are active to avoid the much larger pumas.

With fewer coyotes and bobcats on the landscape, foxes appear to have seized an opening and were seen more often, which then may have suppressed the activity of their primary prey: rabbits.

These patterns involving an apex predator have been called the “ecology of fear,” since the mere perception of a large predator can cause other animals to change their behavior, which then affects the other organisms that they rely on for food.

In this study, the findings at the lower level of the cascades – the indirect influence of mountain lions on vegetation, foxes, and rabbits – are considered provisional, as other influences such as changes in fog and temperature could not be ruled out.

Yet the mountain lion presence had a clear impact on deer, coyotes, and bobcats – and therefore, on the ecology of Jasper Ridge, underscoring the role both of apex predators and small preserves. In the U.S., 82% of protected areas are under 5 square kilometers (about 2 square miles), so they will likely be critical spaces for wildlife and plants as rapid urbanization continues, said Rodolfo Dirzo, study co-author and Stanford professor of biology in H&S.

“Maintaining sites where there is an entire community of animals, from predators to prey to the prey’s resource base, is very important,” he said. “When one piece is missing – and it’s typically the top predators that require larger areas and are more sensitive to human impact – we will no longer have fully functioning ecosystems.”

Mystery of mountain lion motivations
Why the mountain lions started to frequent Jasper Ridge is unknown. One theory is that the female mountain lions found the preserve to be a safe place to raise their young, as a mom with kittens has been spotted on camera during the study. Whatever the reason, they are only visitors. Mountain lions have a huge range in the Santa Cruz Mountains from 20 to 170 square kilometers (about 8 to 66 square miles). Jasper Ridge is far too small to have its own puma population.

Despite the occasional high-profile sighting of a mountain lion in San Francisco or in the suburbs, they tend to stay far away from humans, said Elizabeth Hadly, the study’s senior author and Stanford professor emerita of biology in H&S. They are also nocturnal, so they are not often on the landscape when people are active.

“Pumas are afraid of our smell and our sounds; they don’t like to see us moving,” said Hadly, who is also the former faculty director at Jasper Ridge. “Pumas use all of their senses to avoid humans.”

Humans are the No. 1 cause of mountain lion deaths, either through hunting or car accidents, Hadly pointed out.

“Clearly, we exert our own ecology of fear,” she said. “Humans are the ultimate predator on almost every landscape.”

Florida panther vs wild hogs

 In March 1987, Florida biologists released twelve radio-collared wild hogs into the Everglades to see if they could feed endangered Florida panthers by giving them something easy to kill. Bears ate two. An alligator ate one. Hunters poached three. A panther finally killed one after 117 days. By then, most of the hogs were already dead from everything except the animal they were supposed to feed.

The experiment came from a real problem. Florida panthers living south of Alligator Alley in the Fakahatchee Strand and the southern Big Cypress were in worse physical condition than panthers to the north. Food habits studies by the Florida Game and Fresh Water Fish Commission showed why. Panthers north of the highway ate mostly white-tailed deer and wild hogs, large prey with high caloric return. Panthers south of the highway were living on raccoons and armadillos, smaller animals that provide less energy per kill. The southern panthers were nutritionally stressed in the commission's language. In plain language, they were not getting enough to eat.

The idea was to test whether releasing hogs directly into occupied panther home ranges could supplement the prey base. The commission selected twelve castrated, pseudorabies-free wild hogs, fitted them with radio collars equipped with mortality signals, and split them into two groups.

On March 27, six hogs were released into the Fakahatchee Strand State Preserve within one kilometer of a radio-collared adult female panther. On March 28, six more were released in the privately owned Golden Gate area south of Alligator Alley within 200 meters of a different radio-collared female panther and her eight-month-old male kitten. The researchers monitored the hog collars every other day from the air, flying the same telemetry routes they used to track panthers. When a collar transmitted a mortality signal, a ground crew went in the same day to examine the carcass.

The swamp ate the experiment.

Two hogs were killed by black bears. One was killed by an American alligator. One was found eviscerated and partly covered with debris, which is consistent with a panther kill but could also have been a bobcat or another bear. Three hogs were killed by hunters, identified by knife marks on the radio collars. Two collars failed entirely and the hogs were never recovered. Two more collars were found on hog carcasses with no sign indicating what killed them.

One panther killed one hog. It happened 117 days after the release, nearly four months into the experiment, and was preceded by the deaths of at least eight of the other eleven hogs. The kill was made by a radio-collared adult male panther, not by either of the two females the hogs had been released next to. The females had home ranges of 160 to 350 square kilometers. The hogs stayed within four kilometers of their release sites.

The math was simple and unfavorable. The panthers they were meant to feed moved across enormous ranges while the hogs sat in one small area. The chances of a specific panther encountering a specific hog on a given night were low despite the radio locations showing both species in close proximity.

David Maehr and his co-authors at the commission published the results in the Florida Field Naturalist and concluded that the low number of released hogs made definitive conclusions impossible, but that the one confirmed panther kill suggested very large-scale releases might increase the prey base.

They also noted the obvious problem. The biological consequences and economic costs of large releases of hogs makes this a debatable management alternative. Releasing hundreds or thousands of hogs into the Everglades to feed panthers would simultaneously create an invasive species problem in a national preserve that was already struggling with feral hog damage to native vegetation and hydrology.

The experiment was never repeated at scale. The panthers south of Alligator Alley continued eating raccoons and armadillos. The genetic rescue that eventually saved the Florida panther population came not from supplementing the prey base but from supplementing the gene pool, when eight Texas cougars were brought in eight years later. We covered that story on this page with TX-101.

Twelve hogs were released to feed panthers. Bears, alligators, hunters, bobcats, and unknown causes killed eleven of them. One panther ate one hog four months later. The swamp took everything first because the swamp does not care about experimental design, and every predator south of Alligator Alley was hungry, not just the one the experiment was trying to feed.

Source: Maehr, D.S. et al. (1989). "Fates of Wild Hogs Released into Occupied Florida Panther Home Ranges." Florida Field Naturalist 17(2):42-43.

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.

 

 

---

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