Tuesday, June 21, 2011

Silent Rattlesnakes

   Dear all:  These replies are in response to a query on what seems to be a common perception that rattlesnakes are evolving or de-evolving due to the increase of the feral hog.  The thought among many ranchers and outdoors enthusiasts is that the snakes that rattle soon become hog chow while those that don't go undetected.  I have been told this on several occasions  by landowners, mainly in an effort to warm me of the "greater danger" a silent snake can pose.

  Anyway here are some of the many responses to that query.

Dear Brush,

It's been more than 25 years since I was told this by my graduate advisor,
Harry Greene, then at UC Berkeley and now at Cornell.  Harry is, among
several major interests in reptile ecology, a student of the feeding biology
of pit vipers.  He told me about the differences in behavior of western
rattlesnakes, Crotalus viridis, in the East Bay hills.  Animals living in
Berkeley (I was surprised to learn that numbers of these rattlesnakes lived
in the city!) were retiring creatures that rarely rattled or threatened in
any way, while snakes living on the east side of the hills were more typical
in that they reacted to the proximity of dogs and people, etc., with
assuming a strike posture and rattling.  Snakes taken from these sources
retained their different behavior in the lab, and I think they bred true-
but I am less sure of that breeding experiment, my memory being something
less than once it was.  The distance between these source populations was
something less than twenty miles.

Harry was regularly asked to relocate rattlers found on campus and in the
city.  I believe it was his policy to pick them up in daylight and return
them to their place of capture after dark some time!

My take on this is that rattlesnakes that call attention to themselves
amongst numbers of people cannot be expected to survive long enough to leave
many descendents.
Wouldn't that be an evolutionary modification, taking hundreds or thousands
of generations, with constant pressure needed throughout the process?
Sounds sort of like the folks who figure that Ivory-billed Woodpeckers have
in recent years become fraidy-cats, so that we can't get good looks
at them. Good story-telling stuff, but I dunno.
Greetings Brush:

I have seen twenty-seven rattlesnakes so far this year - as I am close to deaf
in one ear I almost always see them before I hear them and am glad that I am old
enough not to worry about my own gene pool issues - HAH!   All of them rattled
as I moved closer ... and my area is thick with wild pigs.  It would be a tricky
study to do - as we don't really have any, well-documented before data but this
topic has been bandied about by some of my herpetologist buddies.

Rattlesnakes. Interesting story - I have been told the same by some, shall I
say "rural", coworkers. During my years of fieldwork on the Callahan Divide,
Stockton Plateau, Concho Valley, south Texas, etc., where rattlers are
plentiful, very few have rattled upon coming across them. Growing up, I was
a snake nut, and we commonly encountered rattlesnakes when looking for
kingsnakes, corn snakes, etc. Very few rattled, unless provoked. I rarely,
if ever, "harass" snakes. The only times that I have seen rattlers "buzz" is
when they are prodded or have rocks thrown at them, etc. I have literally
stepped on them without them rattling. Perhaps it's the weather, I don't
know. I have always wondered if most people upon discovering a rattler,
either out of fear or curiosity, incite the snakes to rattle. Whereas,
myself and others of that strange ilk, just give space and pass on by.

Dr. Gad Perry brought the rattlesnake subject up in a class a year ago. I don't know how well documented the non-rattling occurrence is, but it seems as though most herpetologists agree that it is indeed going on. I do not believe that hogs have as much to do with it as people do. With the general hatred towards snakes, people are more likely to kill the ones that they see. If a rattlesnake rattles, it is more likely to be seen. That is what I believe the train of thought is. The huge rattlesnake round-ups certainly don't help.

Dear Brush:   Thanks for bringing that up.  We have both hogs and rattlesnakes galore and have noticed that the snakes just do not rattle like they did when we were younger.  Sometimes they do but at night is when they are most active and we often do not hear the ones the dogs find rattle at all..  It is a dangerous time to be out without a flashlight around here.[ ] .We depend on our dogs.  They do a very good job of finding them.   We really hate to kill any of them but if they decide they want to stay around the house or sheds we don't have much choice. []  We think there is some truth to the theory, I have heard a lot of neighbors say the same thing you are asking about.


Brush:  [].  If the gypsy moths can adapt , why can’t snakes?

Well, between Abilene and Sweetwater there are rattlesnakes that have evolved not to rattle.   Not much to do about hogs.  More about generations-worth of "Roundup" Festivals.  This "a good snake is a dead snake" - mindset is a sad legacy of Homo sapien sapien.  That first book in that Bronze Age desert-religious compilation of books never helped either I suppose.

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