timber rattlesnakes | The Lizard Log

My name is Shawn Snyder and I am currently a senior majoring in Wildlife and Fisheries Science. This is my first and only year working in the Langkilde Lab. During the summer of 2016, I worked under Dr. Chris Howey as a Research Technician studying the effects of prescribed fire on timber rattlesnake populations. This position provided me the opportunity to radio-track timber rattlesnakes, record habitat data on tracked snakes, catch new snakes (extremely fun), learn how to safely tube a venomous snake (even more fun), and conduct vegetation surveys. Also, this position provided me the opportunity to formulate my own scientific question to test! Together, Chris and I thought up a small side-project that I could conduct throughout the summer, which provided me the fantastic experience of going through the scientific process, collecting my own data, analyzing those data, and now writing a manuscript so that I can share those results with the scientific world.

When we first started collecting data for my side-project I was a little apprehensive. Once the data was collected and analyzed I realized that this project was going to take time and a large amount of effort to complete. As the process of analyzing the data and then coming up with a plan for the manuscript began to take shape, I started to feel challenged and nervous by this new task. But weekly meetings with Chris to discuss the process of writing a manuscript have helped immensely. This is my first manuscript and yes it is challenging, but it will all be worth it once we have a finished product. I have ambitions to continue on to a Graduate program after I graduate and this manuscript will help me build my C.V. to apply to Grad schools.

Two yellow morphs bask alongside three black morph timber rattlesnakes at a gestation site. Although we did not use gestating (i.e., pregnant) females as part of this project, this shows you the posture of a basking snake and the difference in color morphs.

My research is investigating if the two distinct morphotypes of timber rattlesnakes (a dark, black morph and a lighter, yellow morph; see above picture) use basking habitat with differing amounts of canopy openness and solar radiation. Previous research suggests that the dark morph evolved in response to thermal limitations in the northern parts of its range. Darker snakes have more melanin in their skin, which allows them to absorb more solar radiation and maintain a higher body temperature than yellow morphs. Yellow morphs having this thermal disadvantage, in theory would have to choose basking sites that receive more solar radiation to compensate for this limitation if they wanted to maintain a similar body temperature to the black morphs. Specifically, I am testing the hypothesis that yellow morphs use basking habitat that has more canopy openness and receives more direct solar radiation (i.e., sun) than basking habitat used by black morphs.

A black morph male timber rattlesnake is seen courting a basking yellow morph female. Once again, the difference in color morphs is striking and has led many to ask what selective pressures are maintaining this polymorphism.

To test this hypothesis, I measured canopy openness over basking yellow and black morphs. I used the timber rattlesnakes that are being radio-tracked for Dr. Howey’s main study as my sample population and placed a flag where a snake was found exhibiting basking behaviors (see picture below for example). We took a picture facing skyward directly over the snake using a camera with a fisheye lens. This lens takes a picture of 180 degrees and captures an image of all of the canopy over the snake (see picture). We can then analyze these hemispherical photographs using a computer program called Gap Light Analyzer to measure the percent canopy openness and the amount of direct solar radiation transmittance (i.e., rays of sunlight) for each basking site. Direct solar radiation is when the sunlight reaches the forest floor with no obstructions from the canopy; as opposed to indirect solar radiation which may be radiation that is being reflected off of clouds, trees, or the ground itself. Our study site is characterized as having a mature Oak/Maple forest with an abundance of closed canopy throughout the area. Both morphotypes use this “closed canopy” forest throughout the summer as foraging grounds, and when they need to bask they must seek out areas where some sunlight is making its way through the canopy. This is where my question becomes very important comparing the habitat used by each morph.

A flag is placed next to a basking yellow morph. An exact description of the habitat is recorded so that I can come back at a later time (when the snake is not there) and take a photo of the canopy directly over where the snake had been.

Two examples of hemispherical photographs taken over two different basking timber rattlesnakes. Both canopies actually have similar canopy openness, but the canopy on the left receives far more direct solar radiation based on the placement of those canopy openings.

So far, my results show that the two morphs use habitat that have similar percent canopy openness, however, there was a difference in the amount of UV transmittance between the basking sites used by the two morphs. Canopy openness doesn’t necessarily designate a “warmer” site because the sun path may not go directly over the gaps in the canopy of that site, thus, the site wouldn’t receive large amounts of direct solar radiation. Black morphs use basking sites that received lower amounts of direct sunlight. They may be able to do this because the greater amount of melanin in their skin provides a greater ability to absorb whatever direct or indirect solar radiation is available more effectively. Yellow morphs use basking sites that received more direct solar radiation. They could be forced to use these sites to compensate for their disadvantage in their thermal ability. I am currently working on writing a manuscript for these data and hope to have it completed by the end of 2016. Stay tuned for more on this manuscripts progress!

Here is a picture of Shawn (holding a Hellbender!!) while on a break from collecting some amazing data.

Given that I am the new guy, it is only fitting that my first blog post provides a little background on myself and my research. So I will use this opportunity to introduce myself.

First, a little about me… As you all are aware, my name is Chris Howey, and given that we have two Chris’ in the lab, feel free to call me Howey. I got my B.S. from the University of Delaware, my M.S. from the University of Central Arkansas, and my Ph.D. from the Ohio University. Originally, I am from New Jersey, but I try my best to avoid that state like it’s the plague (way too many people). I have three older sisters (explains why I’m a little not right in the head), three beautiful nieces, and an adorable nephew. When I’m not chasing down herps, I can be found grilling and smoking meats, drinking beer, and relaxing with my fiancee down in Altoona (everyone is invited to join us!).

Since my undergrad, I have been highly interested in the conservation and proper management of reptiles. It is very hard to get people interested in snakes, lizards, and turtles, and even more difficult to get them to want to ensure the viability of these reptile populations. My research is centered around understanding the needs of reptile species and then communicating these needs to land managers and the public. I strongly believe that publishing one’s work in the best scientific journals in the world cannot save a reptile species from habitat loss, over-harvest, and persecution, but the conservation of reptiles (and other wildlife) can only be done by educating the public and local land managers (However… publishing in the best journals in the world can land you an awesome job). Throughout my undergraduate, graduate, and not post-graduate career my research has focused on understanding how landscape disturbances affect reptile communities and their preferred habitat, and then disseminating that research to the appropriate audiences. Given that the thermal landscape is one of the most important habitat characteristics for a reptile, ultimately dictating the potential body temperature and physiological performances of the animal, I have recently begun incorporating models of the thermal landscape into my research.

During my undergrad, I assisted with research investigating the effects of habitat fragmentation on the eastern box turtle. My Master’s research investigated the effects of commercial harvest on the alligator snapping turtle. Additionally, I studied the habitat use of the alligator snapping turtle during my Masters so that we could further understand what type of habitat must be protected if we are to encourage the recovery of this species. During my PhD, I investigated the effects of prescribed fire on the ecology of the black racer. Currently, I am working on getting those results published; however, I have already begun disseminating those results to land managers… which has led me to where I am at today. For more detail on this past research, feel free to visit my website: chowey.net.

After hearing about my dissertation research, the Bureau of Forestry in Pennsylvania decided that they wanted to know more about how their prescribed fires affect timber rattlesnakes. The timber rattlesnake is not a listed species in Pennsylvania, but many populations are in decline which makes this, perhaps, a sensitive species that could be listed someday soon. However, there are many healthy populations of timber rattlesnakes in the center of the state. So back in 2012/2013, the Bureau of Forestry and the US Forest Service asked if I would help lead a project looking at the effects of prescribed fire on timber rattlesnake populations in the center of the state. … I agreed. I quickly put together a study that would investigate the effects of prescribed fire on the available structural and thermal landscape, understand what habitat characteristics the timber rattlesnake prefers (structurally and thermally), and understand the direct, immediate, impacts of the fire itself on the rattlesnakes if they would be present during the time of the actual fire. … Unfortunately, our project was pushed aside by government budget cuts… But a few months ago, by the grace the snake gods, the project was fully funded! I quickly looked for a lab that I could work out of within the state, and I found a fantastic lab led by Tracy Langkilde. I thought Tracy would be a fantastic person to work with given that she already looks at stress responses to disturbances within the landscape (i.e., introduction of fire ants). Additionally, her work with stress may even add another interesting layer to this project.

For more information regarding my past and future research, please feel free to visit my website: chowey.net

I look forward to working alongside of everyone in the Langkilde lab and sharing with you all the many timber rattlesnake stories yet to come!