Monday, March 30, 2015

In Search of the Coronado Island Rattlesnake

The famous arch of Cabo San Lucas
Baja California is my new obsession. The weather is perfect, the landscape is beautiful, and the ocean is always a stone’s throw away. I just got back from two trips past the border: (1) to Cabo for my honeymoon (where the screams of spring breakers soar through the air), and (2) to Southern Coronado Island in search of the elusive Coronado Island Rattlesnake.

Rattlesnakes live on several islands off the coast of Baja. Many of these snakes are the laid-back island counterparts of their mainland selves, and like other island inhabitants, many have drastically changed in body size from their mainland ancestors. For instance, Crotalus ruber lorenzoensis of San Lorenzo Island is a tiny descendent of the larger mainland Crotalus ruber. The Santa Catalina Island Rattlesnake (C. catalinensis) is one of the more famous species as it is the only known rattlesnake to “lose” its iconic rattle, although lorenzoensis and others seem to be on their way (Radcliffe and Maslin 1975). Poor thing only has one rattle segment to its name! Most of the Baja island rattlesnakes are endemic, which means they occur in one place and nowhere else (and this would be whichever island they inhabit). Although most of these snakes are not endangered, their endemic status is still a conservation concern because it means they have extremely restricted geographical ranges.  

The Catalina Island Rattlesnake (far left) is considered rattleless with only one small segment at the base of its tail. The two island
subspecies of ruber (middle and right) are on their way to becoming rattleless. Taken from Radcliffe and Maslin 1975.

The tiny island of Southern Coronado. Photo: B.J. Putman.

The Coronado Islands are about 15 miles South of San Diego and 8 miles from mainland Mexico. The largest of the four is Southern Coronado Island with just 1 square mile of land. The Coronado Island Rattlesnake (Crotalus oreganus caliginis) is the only snake species on the island*. Not much is known about this species and so my adviser at San Diego State University has collaborated with Dr. J. Jesus Sigala Rodriguez of Universidad Autonoma de Aguascalientes on a new project to learn more about its ecology. Last week, I went with him to the southernmost island to search for snakes that will become part of a long-term monitoring project. We drove from San Diego to Rosarito with minor hiccups other than being stopped by border patrol agents who could not comprehend the unusual amount of wooden cover boards in our trunk. From Rosarito, we took a panga boat to the island. In about 45 minutes we arrived to our destination. The island does not have a dock so our skilled boat driver slowly maneuvered the panga to the closest rocks, which we jumped onto from the boat.
Article correction: the night snake and gopher snake also live on Coronado Island

About to launch our boat in Rosarito, Mexico.

Although the island boasts 1 square mile of land, most of the land is inaccessible because it is so steep. We set off searching for snakes where we could and placed cover boards in areas that seemed promising. Alligator lizards (Elgaria multicarinata) were by far the most commonly encountered herp – we saw way too many to count! We also found a few skinks (Plestiodon skiltonianus). In all, our greatest find was a legless lizard (Anniella pulchra?).

We found 8 individuals of our target species, and not to brag, but this tiny girl found the most out of everyone in our group (brushes off shoulders). I found one of the rattlesnakes next to a dead alligator lizard. I assumed it was about to consume the lizard before I disturbed it. Interestingly though, the lizard’s eyes were missing which suggests it had been dead for some time (probably a day or two). We were thus unsure whether the snake had struck the lizard the day before and had just relocated it or whether the snake was scavenging it.

Left: The beautiful legless lizard.  Right: A rattlesnake found with an eyeless alligator lizard (sorry for my horrible photo editing skills)

Left: Processing a snake while enjoying the view.  Right: Drawing blood from a "tubed" individual.

We implanted a personal integrated transponder (PIT) tag into each snake we found. We also determined each snake’s sex, drew a blood sample, and recorded measurements on body size, rattle size, and mass. The Coronado Island Rattlesnake looks almost identical in pattern and coloration to the Southern Pacific Rattlesnake (C. oreganus helleri), its closest relative. In fact, the island snake is thought to have come from a mainland population of helleri. However, the island species dramatically differs from the mainland species in body size: it’s miniature in comparison. This may come as no surprise as island variants are often smaller than their mainland counterparts, a phenomenon known as Island Dwarfism.  

On top of a hill on the island. About to place down some cover boards.

Island dwarfism is an interesting phenomenon because it goes against Cope’s Rule, the prevailing trend in nature that organisms evolve toward larger body sizes. But islands provide special circumstances whereby they limit animals to a restricted area and also limit the amount of available resources. Hence, compared to giants, dwarfs are able to utilize limited resources more completely and are less likely to succumb to population crashes (Wassersug et al. 1979).

Left: A snake found coiled under a rock.  Right: Same snake tubed and ready for processing.

Island Gigantism also occurs, whereby animals grow in body size when isolated on islands. Gigantism is thought to result from many islands’ lack of large mammalian predators. Without these predators, animals are free to grow and exploit niches that were unavailable to them on the mainland. This is a phenomenon known as Predator Release.

Changes in available prey resources can also influence island dwellers’ body sizes. Across all island snake species, populations that are dwarfed tend to prey on lizards and populations that are giant tend to prey on colonies of nesting seabirds (Case 1978). For rattlesnakes that specialize on small mammal prey, islands lacking small mammals should lead to dwarfism and islands with prey equivalent to or larger than small mammals should lead to gigantism. Another interesting benefit larger-bodied viperid snakes have is their enhanced ability to fast compared to smaller snakes (Meik et al. 2010). Thus, gigantism benefits viperid snakes on islands where prey population sizes frequently fluctuate and/or where prey have relatively high extinction rates. 

Left: A specimen of the giant speckled rattlesnake of Angel de la Guarda.
Right: a specimen of the dwarf speckled rattlesnake of El Muerto Island.
Taken from Meik et al. 2010.
Almost all Baja California island rattlesnake populations are dwarfs. Only one, the Angel de la Guarda Island speckled rattlesnake (C. mitchelli angelensis), has undergone island gigantism. The Speckled Rattlesnake (Crotalus mitchelli) seems to love the island life boasting three descendants (C. m. angelensis, C. m. mitchelli, and C. m. muertensis) on 14 different islands. A study done by Meik et al. (2010) found that the body sizes of island populations of speckled rattlesnakes were best explained by island size (Meik et al. 2010). Smaller islands house smaller snakes and larger islands house larger snakes. The authors found that rattlesnakes typically tend toward dwarfism on islands that are smaller than about 20 square kilometers. In addition, rattlesnakes tended to dwarf on islands where the relative abundance of small lizards was greater than rodents. The authors then suggest that shifts to consuming larger prey (chuckwallas), fluctuating prey densities, and predator release likely resulted in gigantism for the speckled rattlesnakes on Angel de la Guarda Island.

Larger islands tend to house bigger snakes (SVL = snout-vent-length, a measure
of body size). Taken from Meik et al. 2010.

Dwarfism of the Coronado Island Rattlesnake is likely the result of small island size (less than 2 square kilometers!), and a greater reliance on lizard prey (pocket mice are the only known rodent inhabitant of the island). Research from the long-term monitoring program should provide quantitative data to support these theories. In all, islands are awesome (and beautiful) places that can act as “closed” ecosystems providing scientists the means to conduct unique experiments and find new discoveries.


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 Récapet 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.