The flooding northern & central California saw in the first several days of 2023 was, in some cases, the most significant in decades. With this comes the question: how does winter flooding impact rattlesnakes? There are several factors we’ll have to take into account to answer what sounds like a simple question. The first is the age of the snake.
Most young rattlesnakes seeking their first overwintering spot don’t always choose the most ideal place, given the lack of experience. Some common places include fallen tree debris, small rock outcrops, and small rodent burrows. Some of these places work just fine, but often times cold or stormy weather ends up proving the spot insufficient. Relentless wet weather will have certainly proved a lot of first overwintering places inadequate and subsequently dangerous. In some of those cases, the snake will be able to (relatively slowly) swim to safety & pick a new spot on higher ground to await warmer weather to then find an even better spot. However, in some cases, the fast moving water may prove too complex to navigate, proving to be fatal. Plus, the cool (to cold) weather also isn’t all that helpful after they get swept into the open.
Most older (adult or even sub-adult) rattlesnakes overwinter in places more robust, often with or near other rattlesnakes. While most cool season dens in northern California might not have hundreds of rattlesnakes, many will have at least several (to perhaps a dozen). This puts most older, regionally-established rattlesnakes in places above (often times along rocky slopes) or away from washes, streams, and creeks. This should mean flooding of washes, streams, creeks, and rivers didn’t impact most of those more regionally-established rattlesnakes, given they are out of water’s reach during flood events.
One exception (or complicating factor) of regionally-established rattlesnakes becoming impacted would be if a rattlesnakes overwintering place was damaged or destroyed prior to overwintering. This would lead to the displaced snake(s) seeking a new place to spend the cool season. Those last-ditch effort hiding spots could more likely be in flood-impacted areas, thus leading to them becoming washed out. In general, though, most of these regionally-established rattlesnakes likely remained safe from January’s flooding.
Spring & Summer Impacts
As we push the time frame forward into the warm season, we can begin to see different impacts the flooding will have had on rattlesnakes & their habitat. Flooding, in places where it hasn’t happened in several years or more, will likely have washed away plenty of habitat that rattlesnakes find each & return to each summer. Types of summer habitat rattlesnakes enjoy that can be washed away will primarily include fallen trees & other chunky tree debris. In addition, human material such as wood, tin/sheet metal, and other debris that has sat around for years (that is accessible to ground-based critters) are easily floated & washed away in fast-moving flood waters.
As snakes go out this warm season seeking these spots they’ve been using (in many cases for several or many years) and find that they’re gone, they’ll go out seeking new places to replace these old places. This can & will impact folks with who live along and near the rivers/creeks/streams that were flooded during the December & January storms. New places the snakes find may be further away from where water flows regularly in the summer, which is typically where people have homes & other structures, given humans (try to) build at safer elevations near creeks and rivers. Plus, most of the high quality habitat will have been washed away in the winter anyhow, leaving only the remnant stuff closer to human structures that was outside/above the flood zone(s) and not impacted.
Specific areas I’d expect the highest probability of snakes finding their habitat missing or damaged are mostly in the valley, such as the American River from Folsom to Sacramento, the Cosumnes River from Latrobe Road westward, Deer Creek north of Rancho Murieta, portions of Auburn Ravine in Newcastle & Lincoln, portions of Doty Creek in Lincoln, portions of Cook Creek in Lincoln, and the Bear River from Camp Far West Lake westward to its connection with the Feather River. Impacts can also be expected in other low lying areas where creeks, streams, and rivers that flooded widely into the low lying areas. Most rivers and streams in more mountainous terrain stay more confined even when running high, given they’re carved into the terrain. In valleys, however, once flood stage is surpassed, flooding occurs across a much wider swath of land.
Areas to be extra cautious
In short: low lying creeks, streams, washes, and rivers that saw significant rises this winter that haven’t in the last several years. Especially in areas where you can confirm debris that has been sitting for years has been washed away, moved, or damaged. These areas where their habitat got washed away will see a much higher likelihood of snakes winding up in places both new to them and you, when compared to areas with little change to established rattlesnake habitat.