A rattlesnake nestled tightly under a rock overhang in the Methow Valley Ranger District.

A rattlesnake nestled tightly under a rock overhang in the Methow Valley Ranger District. 

TWISP — Rattlesnake hiding places are the site of new Methow Valley research going on this spring, investigating how and why the snakes choose certain locations to shelter from winter cold.

Over the last 10 years, U.S. Forest Service researchers overseen by Methow Valley Ranger District Wildlife Program Manager John Rohrer have located 31 rattlesnake winter dens, using ground searches and radiotelemetry. The work helps protect the animals, which play a vital role in the forest ecosystem, while keeping the public clear of possible encounters.

"We don’t want to create trails, campgrounds, or other amenities in close proximity to known den sites," Rohrer said. "We definitely don’t want people and rattlesnakes congregating in the same spots."

In cold weather, rattlesnakes retire to below-ground sites that scientists call hibernacula, to sleep through winter below the frostline. The Forest Service research is investigating the relationships between elevation, aspect, soils and the amount of sunlight absorbed by surfaces to warm the hibernacula. Most of the winter den sites are in talus or rocky outcrop soils that receive the most sunshine — but not all, says Rohrer.

"It’s interesting that some of the dens are in areas that don’t receive as much sunlight," he says. "We aren’t’ sure why some of the dens are in less conducive sites, but now we know where the majority are likely to occur."

At least six different sized rattlesnakes basking at the entrance of their winter den on a warm spring day in the Methow Valley Ranger District.

At least six different sized rattlesnakes basking at the entrance of their winter den on a warm spring day in the Methow Valley Ranger District.

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