Reptile & Amphibian Forums

This is a field observation made by spending years in the field in the Southern California area.

Many of the Crotalus viridis in Southern California do not rattle their tails in defense. Many specimens found in the field simply stayed still and did not move at all. This has been witnessed time and time again by me in the San Diego County and Orange County areas of California. I actually stepped on a Crotalus viridis that stayed stretched out when I inadvertently stepped on it and never rattled until after capture, when opening its mouth to show the fangs. Even after all that, this individual only made a barely audible rattle lasting for a second.

I believe a process of natural selection is being made in that those specimens that rattle in defense are being killed, whereas those that are not rattling are surviving and producing young that are also reluctant to rattle when they are threatened. It is not completely a natural selection; the human population is causing this trait by killing off those specimens that rattle in defense. With this trait of not rattling being passed on to numerous generations of Crotalus viridis that are surviving to produce more young and the trait of those that rattle literally being wiped out, I believe that the future may produce a Crotalus viridis that no longer rattles, at least in Southern California, where urban pressures are enforcing this trait. Who knows? Thousands of years from now, if this species even survives for that long, we may see a Crotalus viridis without a rattle.

What are your thoughts on this? Has this already been written about?

Michael

You are too quick to come up with "natural selection" as the reason why Crotalus viridis does not rattle, but you are entitled to any theory.

I have witnessed this myself with other species, even very high strung ones like C. atrox. I believe this theory has been postulized before, being that since humans tend to kill rattlesnakes that rattle (being that their presence is made known), snakes that do not rattle or do not rattle so much are maturing and producing offspring, while the ones that do rattle a lot are being killed off before reproducing.

The counterargument could be made that snakes are individuals and while certain species as a whole are prone to being more laid back (molossus) than others (atrox), there are laid back and high strung specimens in every species, and genetics might have very little to do with whether or not a snake rattles a lot or not.

I think I saw an Animal Planet show that mentioned this-there was one rattlesnake show that said rattlesnakes seemed to be evolving stronger venoms(if I remember right they concentrated on Southern Pacifics and mojaves). They did mention that fewer snakes seem to be rattling much if at all, but it was a very small part of the show, and I don't remember if the natural selection idea was mentioned or not as far as whether this was "caused" or coincidence.

I think they rely on there camo to remain undetected, rattling would give them away. I think they save the rattling for when the hiding doesnt work..and if that doesnt work they move on to biting.
Just my opinion.

This is obviously a local selection as way up in Alberta they rattle without hesitation

While a bit of natural selection may be in play here, evolution is measured in the millenia. Humans just arn't worth mentioning when it comes to the big picture... yet. Viridus without rattles? Southern California will be covered by the Pacific before that happens.

It's always nice to hypothosize though, it shows the wheels are turning.

Ian

remember that rattling is an involuntary reaction to an increased stress level as opposed being done intentionally or not(e.g. think of all the times we've seen a crotalid rattle at least momentarily before striking a prey item)