Five Things I Learned While Mapping Rattlesnake Dens

Our National Forests provide some of the most intact ecosystems of the country, but measuring the health of these ecosystems can be a challenge. To gauge the overall health of an ecosystem, managers often target one particular species, and native snakes are one species managers rely on. For much of the country that includes one or more of the 32 species of rattlesnakes found in the United States.

In late April I was able to accompany a Forest Service biologist on two field trips in the Okanogan-Wenatchee National Forest in Washington to map denning sites of the northernmost rattlesnake in the U.S.: the western rattlesnake, Crotalus oreganus.

What did I learn? A lot of very cool things. Here are my five favorite western rattlesnake facts:

1. Washington’s Rattlesnakes Still Rattle. Rattlesnakes have a long history of being persecuted by people. In some areas, like California, snake populations have adapted by cutting down on their warning rattles – this makes them harder to find and kill, but easier to inadvertently step on. Washington’s rattlesnakes retain their rattle. That’s what I call a good snake!
2. A Rattlesnake’s Rattle is Surprisingly Muted. I had seen plenty of rattlesnakes before, but never heard one rattle. I was told you will never mistake that sound: it chills you to the bone. So imagine my surprise when, while I was marveling at the crickets chirping all around me, the Forest Service biologists froze in his tracks and looked around. We were standing in the middle of a denning site, and my crickets were snakes, cautiously alerting me to their presence.
3. Western Rattlesnakes Den Together. Rattlesnakes living in the mountains this far north use a special strategy for surviving the long, cold winters: they den together in groups that can number in the hundreds. Snakes will return to the same den year after year, and they even coil up with other species – it is not uncommon to see a non-venomous western racer snake emerge in the spring alongside the rattlers.
4. Rattlesnakes Bear Live Babies. We all learned in elementary school that, with a few exceptions, only mammals give birth to live babies. Snakes are supposed to lay eggs. Rattlesnakes, however, are the exception to the rule: their extremely soft eggshells break before birth, and their shell-less babies emerge fully developed. Western rattlesnakes can bear only three to six babies at a time. And given the short summer seasons this far north, females average just one pregnancy every three years.
5. The Older They Get, The Greener They Get. Western rattlesnakes start out tan with big brown spots. As they mature, the tan increasingly turns green and the brown fades to grey. By contrast, counting a snake’s rattles is not a reliable indicator of the individuals’ age; rattles can fall off as a snake sheds its skin.