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

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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).

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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.”