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What’s Up with Rattlesnakes on the Front Range?

It may seem like the rattlesnake population is rising, but local experts say increased sightings are due to more human activity in the wild.

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It was a sunny, warm afternoon in mid-October, a couple of days after Denver’s first snowfall of the season, when I pedaled up my neighborhood trail on Green Mountain. There, about 100 yards up, stretched across the trail was a three-foot-long rattlesnake, basking in the sun.

I turned around.

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A little while later, I met a friend to mountain bike on North Table Mountain. About five minutes into the ride, we passed a dark, circular lump on the side of the trail that suddenly started buzzing. We yelped and pedaled furiously onward. A few minutes after that, turning up a switchback, there was yet another rattler, this one about four feet long, tan and shimmering, slithering slowly alongside the trail.

Apparently I had missed the memo about the rattlesnake convention.

Is Denver Facing a Snake Surge?

With the recent rattlesnake bite resulting in the death of 31-year-old triathlete, Daniel Hohs, at Mt. Galbraith in Golden—the first recorded rattlesnake death in the history of Jefferson County—and the subsequent closure of Cottonwood Canyon trail on North Table Mountain, it certainly seems like there are more rattlesnakes than ever around Denver. That’s coming from someone who grew up here and who, before this recent hat trick of single day encounters, had only seen about four in my life.

But local experts point out that it’s not Denver’s rattlesnake population that’s swelling, but the local human population, leading to more sightings and more encounters.

“I don’t think it’s an increase in [rattlesnake] population,” says JeffCo Open Space visitor services manager Mary Ann Bonnell, who has been a local ranger involved in rattlesnake research at Front Range open space areas for more than 20 years. “This time of year, especially when we have beautiful, sunny weather, we have a lot more people out on the trails who aren’t going to skip a day like that.”

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As it turns out, humans aren’t the only ones who like to soak up rays on warm, sunny days after a cold snap. Rattlesnakes—the only venomous snakes in Colorado—have a habit of basking in the sun on or near trails during the fall well into November. “Being a reptile, [prairie rattlesnakes] are ectothermic,” says Tina Jackson, species conservation coordinator at Colorado Parks and Wildlife. “They need to be out when the outside temperature is in the range they prefer. In the summer time that preferred temperature happens at night time. We get a few more reports about them this time of year, when the snake temperature is overlapping with human activity times.”

Don’t be surprised if you’re out on the trail on a warm day in January or February and you spot a rattler.

“It’s not impossible on a warm day in February—and warm for this species may be two 55-degree days when it’s nice and sunny—that a snake may leave its burrow and hang right outside of it,” says Joe Ehrenberger, owner and senior ecologist with Adaptation Environmental Services, a local organization that has been conducting a study on prairie rattlesnake movement in urban open space on North Table Mountain. The study, which began in April, involved capturing 20 adult rattlesnakes and surgically implanting them with transmitters before returning them to their capture sites.

Local Rattlesnake Research Underway

Researchers have been able to track the snakes’ movements with antennas throughout the summer and fall. The goal is to locate maternity dens, and to reach a better understanding of how rattlesnakes associate with trails. A team composed of researchers, volunteers, and JeffCo Open Space staff has taken a handful of interested members of the public out to North Table every Sunday on educational tracking expeditions.

I joined them last Sunday, an ideal day for snake-spotting given the sudden warming trend and sun following two days of freezing temperatures.

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The research team outfitted us (myself and a three other curious tag-a-longs) with snake gators—thick canvas/leather plates protecting the lower leg and ankle. We drove up the North Table access road to the summit where we trekked a short distance to a pile of rocks. Here, transmitters picked up signals from several of the tagged snakes. While a few of the 20 have fallen off the grid—either because they ventured too far underground or fell victim to predators (hawks, owls, coyotes, badgers and even skunks prey on rattlesnakes)—the signals from the implanted transmitters activated on the antennas when the snakes were within 300 feet. It felt a little like being in Ghostbusters.

Liz Rose was another curious guest on the expedition. She’s been hiking North Table Mountain almost daily for 10 years and has encountered numerous rattlesnakes, including one that she accidentally stepped on at this time last year.

“It was a huge snake, coiled up. I was looking at the map and not paying attention and stepped backward right on top of it,” she says. “It made this kind of ‘eep’ sound, but didn’t do anything. It didn’t try to attack. Eventually, it just slithered away.”

This scenario is typical of a human vs. rattlesnake encounter; i.e. harmless. According to Bonnell, of the estimated 6.9 million visitors to JeffCo Open Space parks every year, only one or two are bitten by rattlesnakes. Fatalities are extremely rare. While the details of Hohs’ death are still being investigated, rattlesnake experts suspect that severe allergic reaction had something to do with it.

“If it’s anaphylaxis, it could happen that fast,” Ehrenberger says. “This was a super unfortunate incident. You’re just going for a hike. Nobody expects to die that day. But it’s so rare. The truth is, everybody takes much more significant risk getting in their car to drive to the trailhead.”

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Trail Closure

It was Hoh’s death that led park officials to temporarily close Cottonwood Canyon Trail on North Table as a precaution. In addition to my own recent sightings in that area, the closure came after roughly 20 snakes were seen within a 50-foot radius. Snake pits—à la Indiana Jones—are very real. While the dens around Denver are believed to house only a few snakes, in colder areas where dens are fewer and farther between, hundreds of snakes congregate in the same hole for the winter.

“Jefferson County has historical records of five species of snake going into the same den,” says Andrew DuBois, education specialist with JeffCo Open Space. “Bull snakes, racers, and garter snakes will all den up together for the winter.”

Many of us feel grateful that local authorities are keeping us away from recreational areas literally crawling with venomous snakes. But not everybody is happy about it.

“We had what one would call a high concentration of snakes right next to the trail and it felt irresponsible to keep the trail open,” Bonnell says. “I have now talked to quite a few people who love the park, love that trail. This is insufferable for them. It’s not ok that we’ve closed the trail. I get that. We’re emphasizing that we just lost a visitor. As much as we want to think it’s an anomaly, it’s playing into our decision. We anticipate, based on previous research, that Nov. 15 is a conservative re-opening date. We’ll monitor it and if everybody [referring to the rattlesnakes] goes to bed, we’ll open it early.”

Snake in the Grass

After trekking around the first pile of rocks on North Table Mountain, researchers climbing up and over, waving their metal antennas one way and then the other, the snakes failed to appear. We moved to a different area, adjacent to the large quarry on the summit of the mountain. Here, we once again meandered through the tall grass – some of us stepping very carefully with eyes roving every inch of the ground around our feet. We were told the project’s largest tagged snake had last been spotted sprawled right here in the grass. The researchers climbed around the rocks, aiming their antennas and picking up only faint signals. It began to look like the residents of those storied snake pits would remain hidden.

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Then 16-year-old intern Hunter Johnson, an animal lover who became involved with Adaptation Environmental at age 13, appeared on top of the rock pile. He was jumping and waving, a huge smile plastered across his face.

“Hey!” he yelled. “We found some snakes!”

We all climbed the rocks and took turns peering into the shadow under a large boulder where the slowly moving body of a young rattlesnake was just visible. Mission accomplished.

Cohabiting with Rattlesnakes

On the way down the mountain, six separate groups waved the researchers’ truck down to get the low down on snake activity. One woman with a group of hikers and dogs was especially straightforward.

“Are they out today? Yes or no?”

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“We did see a couple close to the trail…yes,” Ehrenberger said. “Just keep a safe distance and keep your dogs leashed.”

These are pretty much the rules to live by in rattlesnake country.

There have been a couple of incidents in the last few weeks where individuals have taken rattlesnake reduction into their own hands. Creepy and dangerous as they might be, killing them is not the answer. After all, rattlesnakes were here long before we were and serve an important role in the environment. Not only do they help mitigate the rodent population, contributing to the prevention of Lyme and other infectious diseases, but their venom is used to cure heart conditions. Also, interacting with a rattler—even with the intent to kill it—is just dangerous.

“We understand that this is something people fear, and for good reason,” Ehrenberger says. “People probably think they’re doing a public service by killing this animal. But they’re also taking a pretty serious risk. A freshly killed snake can still have a bite reflex, even if its head is severed. And when it’s dead, it doesn’t have a release reflex. It’s the stuff of nightmares. Avoiding snakes—that’s the reaction we’re looking for.”

Rattlesnakes are not out to hurt people. When it comes down to it, they are simple creatures.

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“The lizard brain is a very real thing,” Bonnell says. “Rattlesnakes only have about four ganglia: one for eating, one for sleeping, one for getting warm and one for having sex. There’s this haunting fifth one that comes around sometimes for being prey…warning a predator with the rattle. I’m not trying to Disney-fy a snake. A rattlesnake is a venomous animal. But if you leave them alone, more often than not, they’ll leave you alone.”

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