Yellowstone's beaver population was hit hard by last summer's flooding, but it could rebound/NPS file
Editor's note: This is the final story in the National Parks Traveler's series on beavers in the National Park System. Photos are from the National Park Service, but are not recent.
The call came during the 20th century's first decade: Did the Interior Department have any surplus beavers?
It was an odd request, coming from New York state officials who were inquiring on behalf of the Adirondacks, a ruggedly forested, 5,000-square-mile region of mountains, lakes, rivers, and ponds. Once a landscape thriving with the buck-toothed rodents, the Adirondacks were effectively trapped out of beavers between the 1600s and 1800s, a period when mountain men placed their steel traps in every stream they could wet their feet in. When the call came in to the Interior Department, it was thought that just five beavers had all of the Adirondacks to themselves.
Armed with a $1,000 appropriation from the New York Legislature, the state's Fish and Game Commission was able to buy 25 beavers from the Interior Department. They came from Yellowstone National Park, which over the decades has distributed beaver, elk, bison, and even moose across the United States. While four of the first eight beavers sent in 1907 were dead on arrival, the other four were set free near Old Forge, New York. It was the start of a great success story. By 1915, there were an estimated 15,000 beavers in the region, noted Ben Goldfarb in his 2018 book, Eager, The Surprising, Secret Life of Beavers and Why They Matter. Eight years later, New York state allowed a trapping season, he added.
Beaver Resilience
While Yellowstone continues to be good beaver habitat, it's not as robust as the Adirondacks. Through the decades the population has varied greatly. In recent years, the park's beaver population probably has hovered around 1,000 spread out across roughly 140 colonies. But that number took a blow last summer, as the historic flooding that swept through the northern reaches of Yellowstone likely took out many of those colonies.
Doug Smith, until recently the park's wildlife biologist, flew over the park in October to see how many colonies he could spot and came away with a tally of 65 park-wide, which was down from 108 in 2021. With each colony home to 6-8 individuals, there might be about 500 beavers left in Yellowstone.
Whether those colonies impacted by the flooding return remains to be seen.
"It seems like what they do -- and we don't have any radioed to know -- but I think these big water events, they just find a place to hide out, whether it's in a burrow they've dug on the side of the river or they just find above-ground places," said Smith prior to his aerial surveillance. "Or they just get blown down river and they hang out. They seem to casually just infiltrate back. They're pretty resilient to these natural disasters. That's why I think they're good for what you're writing about. I think they're a good form of ecological restoration because they're so damn resilient."
And they benefit so many other species.
"A beaver pond is going to be an oasis. And it's going to be a biodiversity hub," said Smith. "They always are biodiversity hubs. I mean, it's just amazing. When you add water to any mix, what they do, it's truly amazing."
A beaver pond in the park's Lamar Valley/NPS, Neal Herbert
Though Yellowstone is roughly 10 times the size of both Voyageurs and Isle Royale national, it can't boast as many beavers as those two do, said Smith, who retired in December. Apparently holding back the park's beaver population, the biologist explained, is that they don't like swift currents or coniferous trees for food, and Yellowstone has lots of both.
Through the decades Yellowstone's beaver populations have varied greatly. A 1921 survey turned up only 25 colonies, although that was a limited survey. Thirty-two years later, 21 colonies were identified, but none in the areas surveyed in 1921. In a bid to help the rodents, 129 beavers from the Gallatin National Forest north of Yellowstone were set free in the park between 1986 and 1999. While that helped boost the numbers, the beaver population continued to fluctuate, ranging between 112 and 127, according to the park staff.
Steadily driving beaver numbers upward in Yellowstone has been willow recovery, said Smith, as it gave the rodents a reliable food source. In the 1990s, the effort to return wolves to the park led to a drop in elk numbers, and that allowed willow stands to rebound, and beaver numbers began to climb, he explained. Also impacting the elk population was the presence of other predators -- cougars and bears -- and even elk management by the state of Montana outside the park, explained Smith.
Along with overall lower elk numbers, the predators caused the remaining ungulates to alter their movements and that, too, played a part in allowing willow recovery, said Smith.
"The key was a reduction in the elk population allowed willow to come back, which gave beavers a food source," the biologist said.
From Aspen To Willow
An interesting aspect of Yellowstone's beaver history is that the animals shifted their diet over the decades, from aspen to willow. When Edward Warren conducted his survey in the 1920s, he saw that the rodents' preferred forage was aspen. Today, "virtually all the beavers in northern Yellowstone are eating willow," said Smith.
"So, the story is kind of an abundant population, using willow, a population crash, a long period of time with very few beavers, and then a recovery based on an interaction with elk and predators, but the recovery is entirely dependent upon willow," he explained.
Sometimes the presence of beavers in the park is readily visible/NPS, 1968
Those years when the species' population crashed also created hurdles for beaver recovery.
"Decades with very few beavers changed stream geomorphology. So watching a few of the sites that beavers are reoccupying, they're having a hard time because of stream rescission," said Smith. "The streams have straightened and deepened," making it tough for beaver colonies to get established.
"I've watched one colony bounce around in different locations. They've got good forage, but they can't seem to find a good pond site," he said. In their search for a suitable site the beavers in 2021 moved further upstream on Crystal Creek and were able to dam the stream and create a pond, added Smith.
Whether they survived the flooding remains to be seen.
While some other national parks are looking to beavers to help with restoration or areas impacted by wildfires or overgrazing, at Yellowstone the beavers are just being beavers.
"We probably have beavers at capacity," said Smith. "They're doing the job on their own."
It's a fascinating job, as Warren pointed out in 1922 in a booket he wrote on Yellowstone's beavers.
"The value of the beaver to the Park visitor is something rather difficult to put into words, but the creature has a real fascination for the intelligent tourist. Here is an animal of most interesting habits which was once to be found over the greater part of the United States but has since been exterminated from large areas, yet has left traces of its former presence in such place names as Beaver Brook, Creek, Kill, River, Lake, Falls, Hil], Dam and Meadow," wrote Warren. "It can still be found in abundance in many parts of Yellowstone Park and the surrounding National Forests, affording opportunity for observing its habits and studying: its works. Surely this is a valuable privilege for all who can visit the great Park."
Science coverage from the National Park System is made possible in part thanks to the support of Earthjustice.
Other stories in this series:
Using Beavers To Restore Wetlands In The National Park System
Under The Willows| Beavers Partner With National Parks For Landscape Restoration
Under The Willows | Putting Beavers To Work In Rocky Mountain National Park
Under the Willows | Beavers Return To Bandelier National Monument
Under the Willows | Beavers As A Keystone Species At Voyageurs National Park
A beaver dam in the Southeast Arm of Yellowstone Lake/NPS
