Wednesday, June 22, 2011

Watch Your Step: The Myth of Cottonmouth Nests

            It is hard for many people to imagine something more nightmarish than strolling along the shore of their local lake and stumbling into a nest of Cottonmouths. I believe there is a legend of a water-skier plowing right through one, or perhaps it was a Cottonmouth breeding ball. In any case, although the details escape me, surely we can all agree that he died a painful and miserable death.

Fortunately though, nobody needs to spend much time worrying about Cottonmouth nests. They don’t exist.

A nest is an area or structure where an animal lays its eggs or raises its young. Cottonmouths give birth to live young so they don’t need nests to hold eggs. And, Cottonmouths don’t take care of their young after they are born, so they don’t need a nest for that either.

So, what is the origin of this myth? Perhaps the simplest explanation is that someone noticed a number of baby Cottonmouths shortly after they had been born. In those early moments, the little snakes were probably still clumped together; perhaps mom was there too. But, before long, all snakes would head their separate ways.

Another potential explanation is that what some may think is a nest of Cottonmouths is actually a breeding congregation of non-venomous water snakes. When a receptive female water snake is in the area, she may attract several males, which tend to be much smaller. The competition and confusion of this rendezvous may make it appear as one of the fabled Cottonmouth nests of lore.

Cottonmouths are opportunistic predators, they will eat just about anything and are happy to take advantage of situations that make their prey easier to catch. Due to their close association with wetland habitats and their tendency to prey heavily on fish, they may congregate around ponds as they shrink in size during droughts. In these rapidly shrinking puddles of water, it may appear as though there are very high densities of Cottonmouths in small areas. I’ve suggested this occurrence may explain the myth of Cottonmouth breeding balls, but perhaps it could also explain the myth of Cottonmouth nests.

I believe I’m running out of Cottonmouth myths to debunk…Have I forgotten any?




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This isn't the first time I've written about Cottonmouths.  For a discussion of Cottonmouths allegedly dropping into boats, click here. Or, to read about breeding balls, click here. To learn about where in the world you can find Cottonmouths, and where you can't, click here. Worried about getting chased down by one of these snakes? Then you need to read this. Not concerned about being bitten by a Cottonmouth in the water? You should be.

I wrote about how these snakes are quick to show up when a lot of toads (= food) appear here.  I've also written about accompanying Cottonmouth researchers as they wade through swamps to catch snakes in the spring as the reptiles try to take advantage of the new warmth and at night in the summer as the venomous snakes swam around me.  Finally, I provide some tips on recognizing Cottonmouths from non-venomous watersnakes here.

Cottonmouth pictures are provided courtesy of Fingerprince Prints.

Tuesday, June 21, 2011

Can Cottonmouths Bite Underwater?


Yes.

            
A few years ago, I was asked to comment on a proposed snake exhibit in a local nature-themed education center. The exhibit was going to be a large swampy area, complete with water snakes, Cottonmouths, and various other wetland reptiles, like turtles.  Although I personally would have enjoyed viewing such a display, I warned those at the nature center that the exhibit was unlikely to be very diverse for very long. Eventually, I predicted, the entire display would have consisted of a few very fat and very content Cottonmouths.

Cottonmouths can become abundant in suitable wetland habitats, such as beaver ponds and creeks.  My hunch is that they can thrive in these wetlands because they are not picky about what they eat. And, when an animal eats just about anything, there’s a smaller chance that they will go hungry or compete for scraps with other individuals of the same species. As a result, Cottonmouths can eat, grow large, and reproduce with relatively little holding them back.

Cottonmouths can and do eat insects, frogs, salamanders, turtles, rodents, birds, and other snakes, even including individuals of their own species. But, given their aquatic tendencies, you may not be surprised to find out that their primary prey item is often fish. Since fish spend their time underwater, it is also not surprising that this is where Cottonmouths find and capture them….with their mouths.

Yet, a myth persists that Cottonmouths can’t bite underwater. They surely can, and people should be as careful of them underwater as they are on land. This is not to say that Cottonmouths present a considerable risk or danger to swimmers. No Cottonmouth is so lazy or distracted enough to allow a casual bather to step on it; any snake is likely to be long gone before you even come close. Alternatively though, Cottonmouths may also use a different defensive strategy, specifically floating on top of the water (or on some vegetation) shaking their tails, and flashing their white mouths to discourage you from getting too close. And if that doesn’t convince you to walk away, I don’t know what will. You can’t say the snake didn’t warn you.

             

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This isn't the first time I've written about Cottonmouths.  For a discussion of Cottonmouths allegedly dropping into boats, click here. Or, to read about breeding balls, click here. To learn about where in the world you can find Cottonmouths, and where you can't, click here. Worried about getting chased down by one of these snakes? Then you need to read this.

I wrote about how these snakes are quick to show up when a lot of toads (= food) appear here.  I've also written about accompanying Cottonmouth researchers as they wade through swamps to catch snakes in the spring as the reptiles try to take advantage of the new warmth and at night in the summer as the venomous snakes swam around me.  Finally, I provide some tips on recognizing Cottonmouths from non-venomous watersnakes here.

The first Cottonmouth picture is provided courtesy of Fingerprince Prints.

Much of what I write is based on my experience in the field, however I also rely on the research of others, citations of some relevant scientific articles are below.

Vincent, S., Herrel, A., & Irschick, D. (2004). Sexual dimorphism in head shape and diet in the cottonmouth snake (Agkistrodon piscivorus) Journal of Zoology, 264 (1), 53-59 DOI: 10.1017/S0952836904005503



Monday, June 20, 2011

Are Rattlesnakes Rattling Less Because of Hogs?

Remember the Snakes at Your Service Blog Carnival? Well, our network of bloggers has expanded and organized a bit more (you can visit our website, like us on Facebook, and follow us on Twitter) and this week we started our second carnival: Herps Adapt! This event is all about the unique adaptations of amphibians and reptiles so I've decided to feature this post about whether rattlesnakes are adapting to feral hogs. You can follow me on Twitter and/or subscribe to this blog by e-mail.

The short answer:

There's no compelling reason to think so.

Full column:

In the past few months, I’ve received the following e-mail (or some similar version) several times. Generally, the scene is set in Texas (Coleman), but recently the location was switched to Georgia (Ohoopee River, Vidalia, or Lyons).

“We have killed 57 rattlesnakes on two separate ranches this year. 24 @South bend & 33 @ Murray , since mid May. Not one has buzzed! We provoked one fair sized boy with a stick and he coiled & struck at the stick a couple of times before he buzzed up and rattled. The purpose of this explanation is that I have been hearing the same from fellow ranchers and hunters in regards to the lack of warning with rattlesnakes. 

    
I had lunch with a friend today and he offered a theory about the fact that these bugs aren't rattling anymore. He raised pigs for years and reported that when he would hear a rattlesnake buzzing in the sow pen, the sows would bee line to it and fight over the snake. For the uninformed, pigs love to eat rattlesnakes. Therefore, the theory is they are ceasing to rattle to avoid detection, since there are plenty of pigs roaming the countryside. “

  Our first warning that we should be skeptical is the photograph that frequently gets attached to this e-mail. The featured snake is an eastern diamond-backed rattlesnake from Cooperville, Georgia (covered here). The closest this species gets to Texas is eastern Louisiana, and they are extremely rare there.

  But what about the text? Is it reasonable to suggest that rattlesnakes aren’t rattling much anymore because the noisy individuals are being eaten by pigs?

   Pigs are a relatively recent phenomenon in North America. Many were brought over from Europe as people from that part of the world colonized this continent. Many more pigs have escaped from farms and hunting preserves in the past few hundred years. Today, hogs can be found virtually everywhere across the United States. Once in the wild, animals that escaped from farms rapidly become feral and nearly unrecognizable from the barnyard creatures we know and love.  Hog populations can quickly form and grow as pigs reproduce and take advantage of their surroundings.

  And take advantage they do. As the habitats of North America did not develop with hogs, they are often unable to adjust to them. In the course of foraging for food, hogs are thought a destructive force, particularly as they root around in sensitive wetlands. Among many detrimental effects, the severe decline of some salamanders in the southeast has been attributed to the presence of hogs. So, it’s not out of the question to suggest that pigs (again, a relatively recent phenomenon), are causing changes to rattlesnake populations. But, let’s investigate this further.

  The first question is whether pigs eat rattlesnakes at all. Aren’t rattlesnakes equipped with enough potentially deadly venom to discourage pig predation? Apparently not. Although pigs are known to eat many amphibians and reptiles, there are few reliable observations of pigs eating rattlesnakes. But, I did find some accounts in a couple ancient rattlesnake tomes (ancient, but perhaps remaining the definitive source of information on these animals: Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind, Second edition (2 volume set)). So, we know that although being bitten by a rattlesnake is surely an unpleasant experience, the prospect is not enough to dissuade a pig from eating one of these animals on occasion. Pigs primarily eat vegetation, so it is unlikely that rattlesnakes represent a major component of their diet, but anyway...

  Let’s move on to the next part of the e-mail, specifically the suggestion that rattlesnakes are not rattling anymore so as to avoid detection by pigs. This is where we seriously begin to strain credibility.

  A major assumption of this statement is that rattlesnakes used to rattle a lot and they don’t now, regardless of the cause. No study has ever investigated this potential phenomenon, and it is a big stretch to say it’s happening at all. It’s easy to find people offering personal observations one way or another. So...I’ll add mine! 

  Although I don’t have personal, historic experience with rattlesnakes, I have plenty of experience in recent years in an isolated area of southwestern Georgia, before there were many feral pigs. On this site, there were lots of eastern diamond-backed rattlesnakes (as well as timber rattlesnakes), and they rarely rattled unless they were disturbed. I have been within a few feet of rattlesnakes on several occasions (that I knew of, surely there were many that I did not even detect) and they were unlikely to make any noise or even move a muscle. We can’t attribute this behavior to pigs, because they were virtually absent.

  Why didn’t these animals rattle whenever I came close by? Because rattlesnakes don’t want to advertise their presence, they have nothing to gain by attracting attention. If a potential predator walks by a highly camouflaged rattlesnake without ever noticing it, well, that is quite alright with the rattlesnake. Only when the potential predator has discovered the rattlesnake will the snake benefit by giving a warning rattle.  That is another reason I’m skeptical of the story in the e-mail. A hidden rattlesnake in the woods is unlikely to rattle when there is a herd of pigs nearby (presumably causing the pigs to “bee line” towards it).

  Some readers will likely be quick to point out that there are exceptions to this rule, and sometimes rattlesnakes rattle when they’re not being disturbed. I agree, but I’m talking in general terms.

  In any case though, for the sake of furthering the discussion, let’s assume that pigs are eating rattlesnakes that rattle. Is it likely that rattlesnakes are ceasing this behavior to avoid detection? No, it’s not likely at all. This statement assumes that individual rattlesnakes are learning that there is a big disadvantage to attracting a pig’s attention (a similar assumption is required to accept the myth that baby rattlesnakes are more dangerous than adults). For a rattlesnake to learn there is a disadvantage to rattling, wouldn’t it have been necessary for that rattlesnake to have some unpleasant (but not fatal) experience with a pig? Not only that, it would have been necessary for an individual snake to learn, over several occasions, that rattling leads to pigs finding them, and they don’t like that, so they should stop rattling. 

  Presumably, these pigs wouldn’t be very efficient at killing the snake, and if the snake is surviving numerous encounters with pigs, then maybe they’re not such a concern after all.  Laboratory experiments make this hypothesis even harder to accept. Some researchers have demonstrated that by repeatedly disturbing a rattlesnake over a short time period, it becomes less likely the rattlesnake will rattle. The snakes get used to the disturbance. But, the next day, the snakes start rattling like nothing had ever happened, they don’t remember or learn what they had gotten used to the day before.

  A separate question is whether pigs are leading to populations of rattlesnakes changing their behavior. For example, if the tendency for a rattlesnake to rattle had a genetic component, then if pigs are eating rattlesnakes that tend to rattle they are influencing the gene pool. Remaining rattlesnakes would be those that are genetically predisposed to staying quiet, these animals would be more likely to pass on their genes, resulting in even more quiet rattlesnakes. This would basically mean that rattlesnakes are evolving. This seems potentially feasible, but it should be noted there is no evidence that rattling behavior has anything to do with a snake’s genes, or that pig predation is intense enough to affect populations to such an extent.

  In conclusion, although pigs may eat rattlesnakes, let's say it's unlikely they're influencing rattlesnake behavior because 1) we don't even know for sure that rattlesnake behavior is changing for any reason, 2) rattlesnakes generally rattle to deter predators, not attract them, 3) rattlesnakes don't learn to stop rattling, even if the unlikely scenario would emerge that would facilitate learning, and 4) there is limited evidence to suggest there is a genetic component to rattling, or even if pigs are exerting a powerful enough effect to alter rattlesnake gene pools.

  Feral pigs are a destructive force, having invaded many sensitive habitats, yet the effects of these invasions are not yet fully-understood.  However, there will likely be many additional studies on the subject, as it is unlikely pigs are going anywhere anytime soon....


Interested in reading about a fellow Auburn Tiger's experience hunting wild pigs across the country? Check out this book: Year of the Pig



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Much of what I write is based on my experience in the field, however I also rely on the research of others, citations of some relevant scientific articles are below.

Means, D., & Travis, J. (2007). Declines in Ravine-inhabiting Dusky Salamanders of the Southeastern US Coastal Plain Southeastern Naturalist, 6 (1), 83-96 DOI: 10.1656/1528-7092(2007)6[83:DIRDSO]2.0.CO;2


Jolley, D., Ditchkoff, S., Sparklin, B., Hanson, L., Mitchell, M., & Grand, J. (2010). Estimate of herpetofauna depredation by a population of wild pigs Journal of Mammalogy, 91 (2), 519-524 DOI: 10.1644/09-MAMM-A-129.1

Place, A., & Abramson, C. (2008). Habituation of the Rattle Response in Western Diamondback Rattlesnakes, Crotalus atrox Copeia, 2008 (4), 835-843 DOI: 10.1643/CE-06-246