Reptile & Amphibian Forums

Here's something I posted in more detail on the Water Snake forum, but it may be of more general interest:

After surveying the snake population of a local wilderness area in central OK for several years, it is painfully apparent that both species of the genus Nerodia (water snakes) have disappeared!

Diamondback and Plainbelly (Blotched) water snakes, which were abundant as recently as 2000, can no longer be found. Haven't seen a single specimen of either since 2001. Numbers of other genera/species seem to "ebb and flow" (up one year, down in others), but the others at least have maintained a presence within the wilderness area.

Has anyone else noted a similar disappearance of a specific genus/species in areas where they once were abundant. Is this part of a longer-term cycle, or is it an irreversible extirpation?

I've considered several possibilities - an influx of predators, disease/plague, water contamination, human intervention - but none of these seem to explain why ONLY water snakes have been affected. There's a small lake, but virtually no evidence to suggest pollution or other contamination. Turtles, frogs, fish, etc. continue to thrive.

I welcome the thoughts or ideas of others on this.

michaelb

That two species of snakes would disappear in two years without other species being affected. It would take an environmental disaster of cataclysmic proportions to cause that, and it certainly wouldn't go unnoticed, plus other species would go along with them. It may be that at that particular lake, their preferred food source is now more scarce, so the majority of them moved to another lake, creek or river.

What is the size and topographical makeup of the study site? What was the methodology of your population survey? How many people did you have participating in the field studies and how was the study site approached? Did you use gridded topo maps? Did you keep detailed field notes of when (date, TOD, etc.) specimens were found and where, weather conditions, etc. from 2000 and before? What time of year did you conduct the survey, and over what period of time? What notes were made as to the presence and abundance of food items for the target species? Were sympatric species noted?

The most likely thing is that you just didn't find any water snakes, but they are still there if they were in 2000.

Thanks for your comments. I've posted again to the Water Snake forum; that should answer many of your questions. This isn't a rigorous study, but I'm convinced nonetheless that it's not a matter of them (Nerodias) being there and staying out of sight. They're just not there any more. If they were, I'd be seeing them, as often as I visit the area.

It's a small enough area (1/4 sq. mile) that I suppose a handful of rednecks could reduce the water snake population by themselves. They wouldn't even need a reason, although they might have thought the place was overrun with "water moccasins" and decided to do something about it. I suppose it could be that simple.

Not sounding a mass-extinction alarm here or anything, but just sharing a local observation. If similar observations start coming in from other areas, _then_ we may have somthing to worry about.

I have noticed the same decline here in Texas with the diamondback water snake. When i was a child into my late teens they where everywhere, you could count on one or more being under just about anything you flipped ove beside the water. I have read simular declines up north, and even read that in some states the diamondback water snake is on the protected species list. Happily i did happen upon a sub adult D/B two days ago while trying to spot the mysterious alligators that everyone keeps seeing at our nature preserve. Got some cool pics of the little guy. But yah, if anybody has a clue as to whats the deal, clue us in. My suspition is that they are being mistaken for cotton mouths and are being killed off. Skinner

Yep, the mistaken identity thing could explain it on a local scale like this. Even though we're just outside the range of the cottonmouth here (the published range, anyway!) water snakes just seem to get a bad rap wherever they are.

All snakes get a bad rap. It's unfortunate.

And...just because you are outside of the Cottonmouth's published range, don't take that to mean you won't see one. I've found them in areas you would never expect to find one, as much as 75 miles outside the published range, and in habitat you wouldn't expect to be favorable to them. There are isolated populations way outside of the normal range, esp. in Kentucky and Missouri and I've heard of one in Illinois. They are apparently fairly mobile snakes and will use small waterways to reach places you wouldn't expect.