Saturday, February 7, 2015

What do the Grammys and The Fear of Snakes Have in Common?

The Grammys are this Sunday and one of my favorite artists, St. Vincent, is nominated for Best Alternative Music Album. The first track on her album is entitled "Rattlesnake" (which is awesome), but its lyrics may not represent snakes in a good way. This song is about the fear and intensity of being isolated in the wilderness for the first time. She wrote the song after an experience in the American Southwest where she wandered alone through the desert one night and thought she heard a rattlesnake’s rattle. Based on the song’s lyrics and music composition, this was a frightening experience for her. Would this song have a different title if rattlesnakes were not feared by people?

Here are the lyrics to the song Rattlesnake by St. Vincent:

Follow the power lines back from the road
No one around so I take off my clothes
Am I the only one in the only world?

I see the snake holes dotted in the sand
As if the Seurat painted the Rio Grande
Am I the only the one in the only world?

Sweating, sweating no one is behind me
Sweating, sweating no one will ever find me

The only sound out here is my own breath
And my feet stuttering to make a path
Am I the only one in the only world?

Is that the wind finally picking up?
Is that a rattle sounding from the brush?
I'm not the only one in the only world

Running, running, running rattle behind me
Running, running, no one will ever find me
Running, running, running rattle behind me
Running, running, no one will ever find me
Sweating, sweating, sweating, rattle behind me
Running, running, no one will ever find me
Sweating, sweating, sweating, rattle behind me
Running, running, no one will ever find me

A broad theme of the song centers on a fear of snakes. Is this fear justified? Long long ago, snakes were in fact a predator of early man (and still prey on some hunter-gatherers today!) and so we hold an evolutionary reason for why we would be afraid of snakes. In the song, she becomes frightened after hearing the rattling sound of a rattlesnake. A lot of studies have focused on fear responses related to seeing to snake, but not hearing the sound of a snake. Is our response to hearing a snake different from when we see one? 

Rattlesnakes are good at hiding in the grass. Our ability to quickly detect 
snakes is important. Photo by B.J. Putman 

Past studies have shown that humans possess the keen ability to quickly detect hidden snakes, and this has led to the Snake Detection Theory which states that our strong need to detect snakes in the past has led to human’s crazy snake-finding skills which are no longer necessary for our current survival (Soares and Esteves 2014; Van Strien et al. 2014). However, our ability to find snakes quickly does not explain the psychological fear many people have towards snakes (Tierney and Connolly 2013). Some scientists believe that the fear of snakes is transmitted from mother (or father) to the child – it is a learned response. In support of this, both human and primate infants show greater fear of snake-like objects only after observing fearful reactions to the objects by their mothers (Mineka et al. 1984, Gerull and Rapee 2002)

Our fear of snakes stems largely from cultural learning.
The Snakes In Hats Tumblr is trying to change people's perception of snakes,
cause how can you NOT love animals wearing tiny hats? Adorable.

As past studies have shown, the fear that occurs after seeing a snake is likely culturally learned (unjustified), but the fear that occurs after hearing rattling may be justified. Little to no studies have been done on human responses to rattlesnake rattling, but research on other animals suggests that hearing a snake can indeed be startling, but differs from seeing a snake.  

As an example (and plug for my own study system), ground squirrels respond fearfully to rattlesnake rattling. They can even discriminate between more and less dangerous rattlesnakes just based on sound. Larger more dangerous snakes produce rattling with higher amplitudes and lower frequencies – louder and lower in pitch – than smaller snakes. In addition, warmer more dangerous rattlesnakes produce louder rattling with faster click rates than colder less dangerous rattlesnakes (Rowe and Owings 1996). In one study, squirrels tail flagged and stood alert more following playbacks of recorded rattling sounds from more dangerous snakes (Swaisgood et al. 2003). 

Both warmer snakes and larger snakes have higher amplitude rattling - they are very loud! 
Taken from Rowe and Owings 1996.

Dan Blumstein, researcher at UCLA, has been studying what he calls – The Sound of Fear (dun dun duuuun). He’s looked into the acoustic qualities of sounds associated with fear from the alarm calls and screams of mammals to the soundtracks of Hollywood films (like the music during the classic shower scene in Psycho). His team has found that sounds that make us aroused/jumpy/uneasy contain more noise than neutral sounds. What does that mean exactly? Well, noise doesn’t sound nice because it contains non-linearities, or sound wave distortions. Noise is more complex and more atonal than sounds we consider soothing. We may find noise so disturbing because its acoustic characteristics are more variable and somewhat unpredictable, making us less likely to habituate to them (Blesdoe and Blumstein 2014). Marmots (Blumstein and R├ęcapet 2009), Great-tailed Grackles, (Slaughter et al. 2013), and White-crowned Sparrows (Blesdoe and Blumstein 2014) respond “fearfully” to noise.

The rattle is currently used by rattlesnakes for defense – warning potential predators of the snake’s dangerousness (see previous blog post). It makes sense that the sound of rattling be associated with fear to deter other animals from harming the threatened rattlesnake. Indeed, the rattling of a rattlesnake is noisy and atonal like screams and alarm calls. Its distinct acoustic qualities may justly explain our fear after hearing but not seeing a rattlesnake. The Rattlesnake song itself is jarring because of its use of dissonant and atonal sounds. In the end, we see that St. Vincent was likely expressing a true emotional response to a scary sound, which is also a conserved evolutionary response across distantly related species. 


Tuesday, December 23, 2014

Guest Post #2 - Forget men, do all humans behave like dogs?

Another post from two other students, Dre and John, in my Experimental Ecology class. Their research involved watching the behaviors of interacting dogs at dog parks. Enjoy their guest post below!

We are currently undergraduate students at San Diego State studying biology. We wanted to choose an ecological area of research that would relate to many people so we chose to study man’s best friend. Dogs hold a valuable place in society as they are not only emotional healers but they greatly assist in many duties humans could not do. Understanding the behaviors of canines will give insight to how not only these animals interact, but how other mammals show their dominance. There has long been comparison between humans and dogs so choosing this subject seemed to greatly compliment our research.

Social dominance is a well-­displayed behavior in many mammals. Through our research, we determined that there are many traits that can influence canine aggressiveness. Some of these traits exhibited by canines are very similar to those shown in humans. People have long wondered if traits in humans are related to traits in other mammals, including dogs. Well, we found that there are many common behavioral traits between both species.

Vocal Tone:

Humans display dominance over others through conversation, attitude, and conflict. Some of these traits in humans are similar to those shown in canines. For example, humans show dominance in their vocal pitch (Keating 1985). Keating suggests that the tone in male voices reflects the dominance they display over others. Those with lower vocal tones tend to express more dominant behavior over those with higher pitched vocal tones. Even within social interaction between males, you can notice different aggression types between different vocal pitches. This behavior is very similar to the social dominance exhibited in canines. According to Bradshaw et. al. (1985), canines show dominance through barking and growling. The tone of growling dictates the amount of aggression one dog displays over another. Those canines that have louder toned barks such as Mastiffs are observed to display stronger dominance over dogs with lower toned barks such as Chihuahua’s. Vocal tone is one of the many types of dominant indicators that numerous mammals have in common.


Another way that dominance can be compared in canines and humans is by way of appearance. Appearance in both species is very important during social interactions. Appearance in dogs is based on their breed while appearance in humans varies by many factors including ethnicity. According to Waring et. al. (2013), dominance within humans is displayed differently based on their ethnicity and background. They state that people exhibit different behavioral dominance based on their heritage and ethnic background. Those who grow up in cultures where households are predominantly conservative show significantly less dominant behavior than those who grow up in non­conservative households. For example, they show that people of Asian backgrounds tend to exhibit less dominant behavior due to their upbringing. Dominant behavior between humans can be related to dominating conversation, controlling day plans, and loud vocal tone. Varying dominance among ethnic social groups is very similar to the varying dominance seen among canine breeds. More aggressive breeds such as Boxers and Pit Bulls often show dominance over submissive dogs such as Golden Retrievers and Cocker Spaniels(Guisado and Munoz 2009). Though varied dominance seen within different ethnicities is mainly based on social background rather than appearance, there still exists a relationship between appearance and dominance in both humans and canines.

So, are all men dogs?

Well, no. However, there is definitely something to be said about how humans, including females, exhibit their dominance over others in certain situations. Through our own observational study, there were definitely times when we saw similarities to how dogs interact and how humans interact. Even without words, dogs give off a personality about them that can be noticed. Some dogs are more investigative while others just want to be by themselves. In certain respects, humans are very similar to dogs.

Our Research:

Our research looked into whether certain physical traits correlated to dominance among dog breeds. We hypothesized that larger dogs and male dogs would be the most dominant. In order to determine each sampled dogs level of dominance, we recorded five behavioral traits including urination, stance, growling, tail activity, and rolling on back while observing interacting dogs in a dog park. We used a principal component analysis (PCA) to compile all 5 behavioral variables into one measure of dominance. We then looked at whether dogs of different sizes or sexes differed in this measure of dominance. However, our study concluded that there was no significant differences in the average dominance between male and female dogs, and among small, medium, and large dogs. These findings, even though do not support our initial hypotheses, are also seen in many other canine studies. Many researches claim that they too do not find any relationship between size and sex and dominance in canines.

We hope to compare our research with other ecologists who have conducted similar studies and have noticed similar behavioral patterns. In future studies, we will greatly increase our sample size and focus on just a few breeds of canine. We intend to continue research in this field as we both have strong interests.

Contact Information:
Diandre Labadie:
John Bruner:

Keating,C. 1985. Human dominance signals: the primate in us. Spring Series in Social Psychology 32: 89­108.

Bradshaw, J. W. S., E. J. Blackwell, and R. A. Casey. 2009. Dominance in dogs­ useful or constructive? Journal of Veterinary Behavior 4: 135­144.

Waring, T. M., and A. V. Bell. 2013. Ethnic dominance damages cooperation more than ethnic diversity: results from multi­ethnic field experiments in India. Evolution and Human Behavior 34: 398­404.

Perez ­Guisado, J., and A. Munoz ­Serrano. 2009. Factors linked to dominance aggression in dogs. Journal of Animal and Veterinary Advances. 8: 336­342.

Wednesday, December 17, 2014

Guest Post - Farming with Earthworms!

I require students in my Experimental Ecology class at SDSU to design and conduct an outreach project related to their independent project research. This post was written by my students, Connor and John, as their outreach. They studied whether the combined effects of worms and fertilizer in garden soil have a synergistic effect on plant growth. Please enjoy their post below!

Langston University Aquaculture.
You may think that worms are just gross slimy pests that only slither around and creep out grade school kids; however, as you will find out, earthworms are very important in many ecosystems. The Earthworm, Lumbricus terrestris, is used in compost in order to create rich organic wastes - a process known as VERMICOMPOSTING. Earthworms are used in farming and other plant rearing practices because they produce high levels of nitrogen, phosphorus and potassium, which are the limiting factors for the growth of plants. Worms help plants in many more ways too!

University of Illinois Extension.

Disease Suppression

One way that the presence of worms can benefit plants is that they can suppress disease in some fruit bearing plants. In a study conducted in 2004, Johann Zaller found that plants treated with an extract from vermicompost were less vulnerable to a blight disease (Zaller 2012). So the worms acted as a disease fighter for the crops, not unlike the immune system and white blood cells of the human body.  While it’s true that there may be better tools that are available to treat plant disease, vermicomposting offers a method that is 100% biologically safe because no harmful chemicals are used to prevent disease; it’s just good old fashioned worm power! The power of the worm doesn't stop at biological disease suppression; worms are capable of much more.

Mixing/Aerating Soil

Another way these wonderful worms help out plants is by digging their way through the dirt. Their burrows allow for more oxygen and nutrients to reach deeper into the earth and to the roots of plants.  The most significant effect the worms have on the soil that surrounds them is their ability to drastically increase the amount of atmospheric nitrogen (N2).  The worms do this by eating dirt that contains microorganisms that emit the nitrogen in the gut of the worm, and once the nitrogen is emitted, the worm poops out what it doesn’t need to survive, and this poop is very high in nitrogen (Drake and Horn 2007).

Increase in Nutrients

Vermicomposting can provide nutrients that can last twice the life-span of soils that do not contain any earthworms. By starting seedlings on vermicompost instead of transplanting them, the chances of germination occurring increases. In a February 2000 study, researchers measured the effects of vermicompost and compost on plant growth with results indicating that there are improvements using vermicompost, but the amount of improvement depends on the nutrient content (Atiyeh 2000). This is comparable to a child drinking milk, we know that the child will receive calcium to help with strengthening bones, but we do not know how much calcium the child is actually absorbing.

Organic Soil Solutions.

Our Study: Worms vs. Fertilizer

In our study, we wanted to see whether placing worms in planters would yield more growth in pea plants than fertilizer would. After three weeks of collecting data we weren’t able to get a significant difference in the change in growth for the two treatments; however, we did see that planters that had worms in them grew the tallest and the fastest and the planter with the fertilizer treatment produced the highest number of plants. This could mean that using worms instead of fertilizer in small scale systems like home gardens, could be the better option and fertilizer would be the better option for a more grand scale option. 

In conclusion worms can be a real force to be reckoned with when it comes to helping out plants to grow big and strong. Next time you decide you want to plant a nice garden in your backyard, go pick up some earthworms instead of fertilizer to use on your crops!

Atiyeh, R.M., S. Subler, C.A. Edwards, G. Bachman, J.D. Metzger, W. Shuster. 2000. Effects of vermicomposts and composts on plant growth in horticultural container media and soil. Pedobiologia 44:579-590.

Drake, H.L., M.A. Horn. 2007. As the Worm Turns: The Earthworm Gut as a Transient Habitat for Soil Microbial Biomes. Annual Reviews of Microbiology 61:169-189.

Zaller, J.G. 2006. Foliar Spraying of Vermicompost Extracts: Effects on Fruit Quality and Indications of Late-Blight Suppression of Field-Grown Tomatoes. Taylor & Francis Online 24:165-180. 

Friday, November 7, 2014

Many Tales of the Snake Tail

Upon first glance, snakes’ bodies may appear to be one giant tail (or one long body depending on how you look at it). However, snakes actually have a defined tail region which is separate from their main body. The tail starts at the cloaca, the magic hole where defecation, fluid release, and reproduction take place. We have multiple holes for these functions, but snakes only have one.  

The snake's tail is just after the cloaca

So what’s so special about a snake’s tail? Well, because snakes are limbless, their tails fill many of the roles that limbs play in other animals. For instance, the tail is used to grasp onto things, in defense against predators, and as a communication device. Because snakes use their tails for a variety of functions, their tails often look different than the rest of their bodies.

Specialized tail movements are exhibited in more than 70 snake species (Greene 1973). Tail movements usually consist of conspicuous motions of waiving the tail back and forth. Although many species differ in the ways in which they move their tails (slow undulatory motions compared to fast jerky movements), all tail displays probably serve an adaptive function (they benefit the snakes in some way). Many proposed functions for this behavior exist. They are detailed below.  

Many juvenile vipers, including rattlesnakes, use their tails to attract prey in what’s called a caudal lure. Their tails are often brightly colored and mimic insect larvae. The movement of their tails attracts animals that eat insects such as lizards and amphibians. Usually these snakes abandon caudal luring behavior (and their tail coloration fades) once they reach adulthood because their diet switches to mammals which are not attracted to insect larvae (Rabatsky and Waterman 2005b, Reiserer and Schuett 2008). 

Can you tell the Yellow-Lipped Sea Krait's head apart from its tail (left)?  The Spider-Tailed 
Horned Viper from Iran has a lure that looks suspiciously like a spider (right). 

Other snakes use their tails in defense against predators. When attacked, many of these snakes will hide their heads under their bodies and waive their tails in the air. Some snakes, such as the Malaysian Pipe Snake (Cylindrophis rufus), do not just waive their tail at random, but violently strike it from side to side as if it were a head. The idea is that predators will aim for the tail thinking it is the snake’s head and this is beneficial to the snake because injuries to the tail are far less serious than injuries to the head. Many snake’s tails, such as those of the Indian Sand Boa (Eryx johnii.), actually resemble their heads in an effort to further confuse predators. Evidence of more scaring on some snakes’ tails compared to other parts of their bodies supports the notion that their tails deflect attacks away from the head (Greene 1973).

(Taken from Greene 1973)

What’s so fascinating about these tail displays is that they may hold the key to the evolution of the rattlesnake’s rattle. We know that today the rattle is used in defense and serves as a warning to predators. However, debate continues as to why the rattle evolved in the first place. There are two camps, those who believe the rattle first evolved to attract prey then switched to a defensive function and those who believe the rattle has always been for defense.  In support of the “prey -attractant-first hypothesis”, Schuett et al. (1984) state that the rattle pre-cursor must have started out small (1-2 segments) so it would have been incapable of making sufficient noise to warn others of the snake’s dangerousness. In support of the “function-has-never-changed hypothesis”, others point out that no other snake lineages that use their tails to attract prey have ever evolved anything similar to a rattle. 
The Dusky Pigmy Rattlesnake has a yellow tail and a small rattle. 
This tiny snake only has one rattle segment! Photo by Mark Herse.

The only rattlesnake we know of to use its tail (and not its rattle) for both prey capture and for defense in adulthood is the Dusky Pigmy Rattlesnake (Sistrurus miliarius barbouri). This species has the smallest rattle compared to its body size of all rattlesnakes (Cook et al. 1994), and 50% of adults in a typical population cannot produce sufficient rattling sounds because of the smallness of their rattles (Rabatsky and Waterman 2005a)! So these pigmy rattlesnakes may be similar to what rattlesnake ancestors may have looked and acted like. However, we don’t know for sure and debate continues on how and why the rattle evolved. 

Over the many years of remotely filming wild rattlesnakes, I have recorded three individuals exhibiting non-rattling tail displays (all adult Northern Pacific Rattlesnakes, one female and two males). This display consists of slowly flopping the raised tail from side-to-side (see video below).

Strimple (1992) emphasized the importance of collecting precise descriptions of the contextual stimuli that elicit tail displays to better understand their function. I have noticed some common themes among the three incidents I recorded. All snakes were in a loosely-coiled body position. This is different from an ambush coil which snakes employ when hunting prey. Snakes are typically loosely-coiled when shedding, digesting, or recovering from surgery (one snake was recovering from surgery, the other two could have been digesting but I am unsure). Snakes exhibited the display intermittently over several minutes (approximately 2-6 minutes), then left their sites almost immediately after. The cloaca of the snakes appeared swollen when they were displaying. Two snakes were alone when they displayed while the third was with another rattlesnake (both were males) and their tail displays can be viewed in the YouTube video above.

What could be the function of this non-rattling tail display? Although I lack enough evidence to definitively determine its function, I can speculate on the options.

Is it for prey capture?
  • This is unlikely because all snakes were not in hunting body positions when they exhibited this behavior (they were loosely-coiled).

Does it defend against predators? 
  • No predatory threat was visible on camera (although predators could have been close by) when this behavior was recorded. All defensive displays reported in other snake species are elicited by touching or severely harassing the snake (their first line of defense is camouflage). Thus, I remain skeptical that this is a defensive display given that the snakes were not physically disturbed.

Does it communicate with others of the same species?
  • This is possible. The cloaca appeared swollen and could have been discharging scented fluids (which have been shown to affect conspecifics). Perhaps the tail movements laid down the scent? Also in support of this, I recorded the tail display when two adult males were interacting with each other. The presence of one male appears to have caused the other to exhibit the display. Schuett (1997) found that tail writhing is displayed by defeated males after male-male combat in Copperheads (Agkistrodon contortrix), and is assumed to advertise the submission of the defeated male. However, it was not the breeding season and these males were never observed to behave aggressively toward each other. Thus, I remain doubtful that this display was to advertise submission.

I hope to converse with other naturalists and scientists who have seen similar tail behaviors in adult rattlesnakes. With enough anecdotal evidence we may be able to parse out the contexts in which this behavior occurs to generate hypotheses to test its function. 

Please contact me if you have observed this behavior! 



Cook, P. M., M. P. Rowe, and R. W. Van Devender. 1994. Allometric scaling and interspecific differences in the rattling sounds of rattlesnakes. Herpetologica 50:358–368.

Greene, H. W. 1973. Defensive tail display by snakes and amphisbaenians. Journal of Herpetology 7:143–161.

Rabatsky, A. M., and J. M. Waterman. 2005a. Non-rattling defensive tail display in the Dusky Pygmy Rattlesnake, Sistrurus miliarius barbouri: a previously undescribed behavior. Herpetological Review 36:236–238.

Rabatsky, A. M., and J. M. Waterman. 2005b. Ontogenetic shifts and sex differences in caudal luring in the dusky pigmy rattlesnake, Sistrurus miliarius barbouri. Herpetologica 61:87–91.

Reiserer, R. S., and G. W. Schuett. 2008. Aggressive mimicry in neonates of the sidewinder rattlesnake, Crotalus cerastes (Serpentes: Viperidae): stimulus control and visual perception of prey luring. Biological Journal of the Linnean Society 95:81–91.

Schuett, G. W. 1997. Body size and agonistic experience affect dominance and mating success in male copperheads. Animal Behaviour 54:213–24.

Schuett, G. W., D. L. Clark, and F. Kraus. 1982. Feeding mimicry in the rattlesnake Sistrurus catenatus, with comments on the evolution of the rattle. Animal Behaviour 32:625–626.

Strimple P. D. 1992. Caudal-luring: a discussion on definition and application of the term. In: Strimple PD, Strimple JL, eds. Contributions in herpetology. Cincinnati, OH: Greater Cincinnati Herpetological Society, 49–54.