Herp Update: Fall Migration for Snakes – October 8, 2021

On sunny and warm fall days another really interesting and dangerous (for them) herp migration takes place. It is the movement of snakes back to their dens.

The cool nights and shorter days cue snakes that it is time to head to their denning locations and get far enough underground so that they won’t freeze over the winter. If the snake is lucky, this does not require crossing a road, but in many cases, their summer foraging habitats and their denning sites are on opposite sides of a road. We have radio-tracked some large snakes (Timber Rattlesnakes, Eastern Ratsnakes, and Eastern Racers) that traveled a couple miles to return to their denning locations. On the other hand, I suspect that some Common Gartersnakes travel only a few hundred yards to their denning sites.

There is site at the south end of Snake Mountain where I used to take my daughters to see this fall snake migration. It is a relatively quiet dirt road with overgrown wet fields on one side of the road, and a rocky south-facing hillside on the other side. About mid-morning on sunny warm fall days, snakes would warm up enough to start moving across the road to their denning locations. The road surface is both sunny and warm enough to often entice the snakes to linger and soak up some heat. Clearly this is a very dangerous behavior for them.

Our data from this site show that on a 1/2 hour visit to this site on September 19 (1991) we found 39 DeKay’s Brownsnakes on about 100 yards of this road. Sadly, 30 of them had been run over and killed. On September 22 (2019) Deb Laramie reported 29 DeKay’s Brownsnakes on this section of road with 27 dead and 2 alive. She also found 3 Common Gartersnakes and one Red-bellied Snake also on the road surface. On October 9, I visited the site and found 40 DeKay’s Brownsnakes on that section of road. Four were alive, and 36 were dead. The latest snake migration we have seen at this site was October 23 (2017). I suspect they are moving there today and since we have not yet had a frost, they may continue to move for a few more weeks on sunny warm days.

As roads take on more and more traffic, I suspect the snake populations that cross those roads will gradually disappear. Those populations that don’t need to cross roads, or only cross sparsely travelled roads should hopefully persist.

Consider getting out on the next warm sunny day on a quiet road that travels between a wetland or an overgrown field and a rocky, south facing upland. Walking or biking through these areas may well reveal some snake-migration corridors. In any case, keep your eyes open for snakes on roads at this time of year, and if it can be done safely give them a hand across the road. Of course, it you live in western Rutland County, and the snake has a black tail and a rattle, don’t pick them up. Please do report any interesting snakes that you find. Many previously unknown populations of snakes are discovered as a result of road-killed specimens.

Here is a link to a video we made at the Snake Mountain crossing location a couple decades ago (you may notice I look a bit younger and thinner :).


You can also watch it here:

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