The Lizard Log

The Langkilde Lab in Action


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Rattlesnake Research Round-up

One in a continuing series of posts highlighting the work of undergraduate researchers in the Langkilde Lab.

Michaleia Mead

My name is Michaleia Mead, and I am a senior in Wildlife and Fisheries Science, Wildlife Option. This is my first year working in the Langkilde Lab.  I spent the summer 2015 working for the lab on maternal stress of Eastern Fence Lizards.  But currently, in my research under Dr. Chris Howey, I am looking at ecological trade-offs between thermal quality and risk of predation at timber rattlesnake (Crotalus horridus) gestation sites.  A gestation site is the area that a female snake spends the duration of her pregnancy in from early spring, and throughout the summer to parturition (birth of the litter).  These sites typically receive a good deal of sunlight and allow the female to maintain an elevated, preferred, body temperature.

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An adult female found basking at a gestation site later in the year.

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A neonate rattlesnake found at a gestation site.  Note the size of the neonate as it is hiding under a small birch leaf.  Neonates will typically remain at the gestation site for about 1 week, basking in the sunlight, prior to following their mother to a nearby den site.

The “openness” of gestation sites range from very open to densely forested sites, enclosed by many tall trees.  For this study, we identified three sites that were very open and three sites that were more enclosed.  We compared the canopy openness, thermal quality, and risk of encountering a predator between these two types of gestation sites.  In particular, we are comparing the relationship between site openness and thermal quality as well as site openness and the probability of timber rattlesnakes encountering a predator.  Thermal quality is the amount of time that the range of temperatures a rattlesnake prefers overlaps with the temperatures that are available (thermal quality would be better at a site if it provided more time when available temperatures overlapped with preferred body temperatures).  I am testing the hypotheses: 1. Thermal quality of the open sites would be better due to a greater percentage of time that the available temperatures would exceed preferred temperatures, and 2. Risk of encountering a predator would increase as site openness increases.  

Cameras were placed at each of the six gestation sites to monitor rattlesnake behaviors and occurrence of potential predators traveling across gestation sites, despite the fact that bears sometimes take our cameras out…jerks.  We also placed biophysical models at each gestation site to measure the available body temperatures at those sites. Via these cameras, I’ve observed potential predators and also documented potential food sources for the rattlesnakes, such as chipmunks.  We’ve determined that open gestation sites are in fact warmer than more enclosed gestation sites, and the thermal quality of these sites is better.  The improved thermal quality of these open gestation sites may lead to shorter gestation times by gravid females, more successful reproductive bouts, and increased population health.  Contrary to our second hypothesis, we do not see more predators at more open gestation sites; however, we do see more predators as the overall area of the site increases.  This suggests that we may increase the openness of gestation sites in order to improve thermal quality for rattlesnakes, and, as long as we do not increase the overall open area on the ground, risk of encountering a predator should remain constant.  All of the data have not been analyzed, but they are showing signs of supporting the first hypothesis.  I am currently working on writing a manuscript for these data and should be completed sometime in late January.

A red-tailed hawk swoops in on top of a foam timber rattlesnake model (not seen). A yellow-morph timber rattlesnake model is pictured behind the hawk.

A red-tailed hawk swoops in on top of a foam timber rattlesnake model (not seen). A yellow-morph timber rattlesnake model is pictured behind the hawk.

Tommy Cerri

My name is Tommy Cerri, and I am currently a senior biology major. This is my 3rd year working in the Langkilde Lab. My current research working with Chris Howey focuses around the behavior of rattlesnakes and relationship these snakes have with predators in the community while entering into their den (referred to as ingress). The main objective of my study is to observe rattlesnakes of varying ages entering and exiting rattlesnake dens and the relationship these behaviors have with the occurrence of predator visits at those den sites. For this study, we are predicting that:

  1. Adult and juvenile rattlesnakes will arrive to the den before neonates
  2. Predator visits will increase as more snakes begin to enter the den
  3. Snake activity in front of the den will increase positively with environmental temperature and decrease when temperatures drop, and
  4. Snakes will retreat to the den as predators approach.

This research is proving to be important to the scientific community because we are beginning to see some behaviors that have never been documented before.  For example, we are finding that rattlesnakes are very active around the den for at least a couple weeks prior to hibernation.  Additionally, prior to exiting the den, rattlesnakes appear to stay under the overhang of the den and observe their environment.  We are unsure if this observation behavior is to test the thermal characteristics of the environment or to look out for predators.  In addition to this, the study may provide insight into what snake age is the preferred prey of predators within the community.  Snakes varying in age from neonate to juvenile and adult have all been seen coming in and out of multiple den sites that have been studied via different cameras that have been set up facing four different rattlesnake den sites located throughout Pennsylvania and New York.  From these cameras, we are able to see predators that visit the den as well as the behavior of rattlesnakes as they enter and exit the den during the day. While collecting data, this is what the view of the den from the camera looks like.

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Can you spot the rattlesnake in this picture from one of our trail cams?

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In this case, the rattlesnake is only a few feet from the mouth of its den.

In the pictures above we are actually able to see two adult rattlesnakes basking right outside two of the den sites under question. While right now the study is still in its preliminary phase of data collection, we have already observed some interesting trends between snake activity and temperature.  For example, snakes tend to be active outside of the den during both the day and night until ambient temperatures reach a specific threshold (roughly 42 degrees F).  Some of these activities appear to be basking behaviors, however, night time activities are unknown.  As of right now, we are not seeing any trends between predators and specific age-related prey choices, and we have not recorded any predation events. We hope to be finished data collection by the end of December and have a paper reporting the results completed by May.

Stay tuned, as we’ll publish a follow-up here with our official results!

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Bears Are Jerks (and Other Things I Learned Along the Way)

I would have done it differently.  Yeah, I think that is a good way to start this post.  But everything makes more sense in hindsight.

Let me supply the background:  The idea was to set up field cameras in front of den sites and observe timber rattlesnakes while they were returning back to their dens.  We would also record environmental temperatures outside of den sites via iButtons.  Once again, I would team up with fellow colleague Tom Radzio, and for this project we would also get some amazing help from undergraduate Tommy Cerri.  We would correlate timing of rattlesnake ingress and environmental temperatures.  But there is evidence that rattlesnakes don’t just dive into the den and say goodnight; they hang out in front of the den for a few days and mingle with one another, hear stories about each other’s summer vacations, and bask in the few remaining days above 10 °C.  The cameras would capture these behaviors in relation to environmental temperatures.  The cameras don’t have audio capabilities, so we are not able to capture the stories of summer vacation, but you’ll just have to take my word on this fact (#nottrue).  While relaxing in front of the den and basking in the fall sunlight, the snakes may expose themselves to potential predators.  A colleague, Chris Camacho, captured some fantastic pictures last fall showing that predators do in fact visit these den areas (check out more of Chris’ fantastic photos).

Red-tailed Hawk landing in front of a den site with a Timber Rattlesnake in front.

Red-tailed Hawk landing in front of a den site with a Timber Rattlesnake in front.

Fisher checking out den site.

Fisher checking out den site.  These are some pretty carnivorous animals!

Raccoon nosing around the entrance to the den.

Raccoon nosing around the entrance to the den.  It appears it is really looking for something.

Momma Black Bear and her cubs walking past a Timber Rattlesnake den.

Momma Black Bear and her cubs walking past a Timber Rattlesnake den.

So this year, we staked out three den sites with field cameras.  We placed two field cameras at each den site.  The one camera was on a tree about 8 meters from the den.  This camera would capture potential predators as they stopped by to visit the den.  The second camera would be much closer to the den and capture the rattlesnakes as they moved in and out of the den.  However, there was a problem with trying to put a camera so close to the den site… the problem was that there wasn’t always a tree right next to the den.  Problem solved!  I built a wooden stand that would support the camera and keep it focused on the den site.  To standardize things, we used this wooden stand for all three den sites, but kept the second camera farther away on a tree (the picture below is taken by the tree camera and you can see the den camera in the background).

Camera positioned directly in front of rattlesnake den.

Camera positioned directly in front of rattlesnake den.

This stand worked great.  And we soon began to capture a few rattlesnakes as they came back to the den site.

Timber Rattlesnake relaxing in front of den.

Timber Rattlesnake relaxing in front of den.

Rattlesnake basking in front of den entrance.

Rattlesnake basking in front of den entrance.

And then we even began to see some bears as they visited the den sites…

Fir

First Black Bear to visit one of the den sites.  This was a nice bear.  Thank you nice bear.

And then the bears became jerks.

Black Bear sitting in front of camera and bending camera over so that it can gnaw on it... jerk.

Black Bear sitting in front of camera and bending camera over so that it can gnaw on it.  The camera was attached to the wooden stand by a thick metal bolt… the bears just bent these bolts like they were flimsy plastic… jerks.

Bears even tag-teamed the camera at times...

Bears even tag-teamed the camera at times!  Not one, but TWO BEARS!!! …double jerks.

Perhaps the bears just like to mess with novel items placed in their habitat.

Bear Hug....

Bear Hug….

Bear chewing on camera...

Bear chewing on camera…

Bear sitting down and swatting the camera round and round.... jerk.

Bear sitting down and swatting the camera round and round.  REALLY! This bear just sat there for 10 minutes swatting the camera as it swiveled around and around on the bolt…. jerk.

Perhaps the camera and stand actually look like some weird creature that lost its way in the woods.

Maybe this is what the bears see?

Maybe this is what the bears see?

Regardless… we stopped seeing rattlesnakes enter the den….

Our

Our “Den Site” View for the majority of time…. Maybe the snakes will go up in the trees…

We did get some great pictures of the backside of bears though….

Bear Butt... Jerk

Bear Butt… Jerk

So what did we learn?  We learned that you should never place novel items in the woods with bears.  We learned that if you do this, bears will make sure to mess with your equipment, chew on your cameras, and rip apart your wooden stands… We also learned that bears are really really strong!  We learned that bears are really fuzzy…

Fuzzy Bear Legs. ... jerk.

Fuzzy Bear Legs. … jerk.

I learned that I would have done things differently.  If I were to do it all again (which I probably will), I would move all of the cameras to a nearby tree instead of a wooden stand.  After four weeks of bears being jerks, this is exactly what I ended up doing.

Okay, so bears are jerks.  But we did see something interesting here.  We placed the cameras out by the dens well before rattlesnakes began ingress.  For one and a half weeks we didn’t see any rattlesnakes or bears.  Then rattlesnakes began to come back to the dens, and it wasn’t until this time that we began to see bears visiting these same areas.  So there does appear to be a correlation between rattlesnake timing of ingress and bear activity outside of dens.  But are we seeing other potential predators?  Well we don’t know yet.  We have been too preoccupied cursing bears to review all of the videos.  The bears did not mess with the tree cameras and perhaps we will see other potential predators visiting the den sites.  We are excited to finish analyzing these video data and update everyone on what we find (look for Tommy Cerri’s blog post in the future).

There is another interesting bit of information to digest as well: Bears have never been documented as a predator of rattlesnakes.  But we have seen bears swiftly attacking rattlesnake models in the field (see previous blog post).  We have also seen bears visiting other gestation sites and den sites. Would it really be too far-stretched of an idea for bears to attack and eat a rattlesnake?  But there is the possibility that bears just like to mess with novel things that they find in the woods.  There is also the possibility that whatever environmental cue drives rattlesnakes to return to their dens for the winter, also instigates bears to begin foraging for food (other than rattlesnakes) along the hillsides of Pennsylvania.  Regardless, bears are jerks.

Bear and Camera Cartoon


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Wrapping Up A Great Field Season

As the days are getting colder, snakes are slowly making their way back to their dens.  My technicians are still tracking their progress, but little-by-little each of our 15 radio-tagged snakes are getting closer to the location where they will spend their winter sleep.  This summer was a huge success as we collected ecological data for our rattlesnakes in our pre-burned habitat.  Much of this success was made possible due to a great team of technicians: Alyssa Hoekstra, Andrew Brown, Zack Maisch, Alex Dyson, and Mark Herr (lab undergrad extraordinaire)!

Our snakes led us to some great data this past summer.  Males did not disappoint us, and they typically had us hiking over large tracts of land. Sometimes, males were able to travel over 1-km in 24 hrs, up and over large mountains.  Much of this traveling was to find receptive females, and we observed many mating encounters as well as male-male combats!

Male and Female Timber

Large male (black phase) wrapped around a female (yellow phase). Typically males will follow females and attempt to entice her to mate by rubbing his head along her body. This female obviously didn’t want to play those games and just remained coiled. (Photo by A. Dyson)

Females stayed a little closer to the den sites and study area. The females main concern was foraging for food, but sadly none of our females at the main study site were gravid this year. Given the high abundance of chipmunks and mice throughout central PA this summer, I would not be surprised if many female rattlesnakes were gravid next summer.  It is believed that good reproductive years for timber rattlesnakes typically follow good food years.  Although we were not measuring small mammal abundance last year, I suspect it was lower than this year. Following the conclusion of our project, we may be able to shed some light on this relationship between rattlesnakes and their prey.  Additionally, prescribed fire can enhance small mammal abundances, which may lead to increased reproductive rattlesnake fitness!

Rattlesnake Eating Chipmunk

Rattlesnake consuming a chipmunk… Alvin!!!! (Photo by Z. Maisch)

In addition to following the snakes around, we also took some time to characterize the pre-burn study sites and the available resources for timber rattlesnakes.  We measured small mammal abundances, operative temperatures, available vegetation, and acorn mast production.  We will compare these available habitat characteristics to next year’s to see how these variables change based on year-effects and the prescribed burn.

chipmunks in tomahawk

Two chipmunks captured in a Tomahawk trap. Each small mammal receives an ear tag so we can identify it at a later data when it is captured again. This mark-recapture technique allows us to measure small mammal abundance throughout the study area. (Photo by A. Dyson)

In addition to the prescribed fire project, we also embarked on two new projects with the help of Tom Radzio!  Tom is a colleague from Drexel University, and he is using cameras to observe tortoise behavior outside of burrows in the southeastern United States for his dissertation.  Tom was gracious enough to loan us a few cameras so that we could embark on these great, new side-projects.

For the first side project, we are currently looking at the ecological trade-offs between thermal resource acquisition and predation at gestation sites of various sizes.  We collected some great data regarding potential predators, including black bears, bobcats, raccoons, and hawks.  Whereas we have already pulled all of our cameras from the field, we are still collecting data from these videos.  Currently, I have a great team of undergraduates assisting me with this process, including: Mark Herr, Michaleia Mead, and Tommy Cerri.  We hope to have all of these data collected and analyzed by the end of November!  We are predicting that we will see a higher amount of predator activity at more open, larger gestation sites, but we will also find higher quality thermal habitat at these same sites as compared to smaller, more enclosed gestation sites.  We are looking forward to the results!

Bobcat at Study Site

Bobcat walking through a large, open gestation site. Whereas the bobcat did not show any interest in the foam, rattlesnake models that we placed at the site, the mere presence of the predator suggests that an encounter is possible.

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A black bear attacking a foam model at an enclosed, smaller gestation site. The bear first approached two foam, rattlesnake models and swatted off their heads. It then bit two more models (one shown here) before taking off out of the gestation site.

For the next side project, Tom Radzio and I are looking at when rattlesnakes decide to go back into their dens, how this correlates with environmental temperatures, and if predators are attracted to these den sites during this time of rattlesnake ingress.  We are currently collecting data at these den sites and we have a great undergraduate, Tommy Cerri, who is assisting us with analyzing these videos.

Rattlesnake basking in front of a den site. If you look closely you can see some small grey iButtons recording environmental temperatures.

Rattlesnake basking in front of a den site. If you look closely you can see some small grey iButtons recording environmental temperatures.

This fall will be filled with a lot of data analyses, writing, and hopefully a few published results. Stay tuned as we finish up a few of these projects.  I will make sure to update everyone on the results to each of the finished products.

Field work in action! Me capturing a small timber rattlesnake. (Photo by T. Langkilde)

Field work in action! Me capturing a small timber rattlesnake. (Photo by T. Langkilde)

This post originally appeared on chowey.net!


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Rattlesnakes and Vernal Pools

Image 2Another field season is underway and things are getting crazy!  This summer, I will be conducting three big projects, but luckily I will have the assistance of a small army of technicians.  The first project will focus on the habitat use and thermal biology of the timber rattlesnake and how prescribed fire may affect the availability of these preferred habitat characteristics.  This summer we will radio-track rattlesnakes to determine thermal and habitat preferences.  Next year, the study sites will be burned, and I will determine if these post-burn landscapes provide more or less habitat fitting these preferences.  So far we are off to a great start! We have captured 21 rattlesnakes and we are radio tracking 5 males and 4 females (we hope to get a few more females).  Next week we will begin to characterize the available habitat surrounding the rattlesnakes as we will begin vegetation surveys, measuring operative temperatures, and small mammal trapping.

Image 5In addition to investigating the effects of fire on timber rattlesnakes, I am also looking at the effects of prescribed burning on vernal pool amphibians.  From time-to-time, prescribed burns are conducted right next to a vernal pool.  This disturbance may reduce canopy cover over the vernal pool, raise temperatures within the vernal pool, and change water chemistry.  Long-term effects may also include changes in soil composition surrounding the vernal pool which may lead to more run-off into the vernal pool.  To determine these effects more clearly, I am measuring the physio-chemical characteristics of 4 vernal pools (2 that will be burned over next spring and 2 that will remain untouched).  I have deployed weather stations in each vernal pool that will track water temperatures, air temperatures, relative humidity, wind speeds, rain fall, and amount of solar radiation reaching the vernal pool.  I am also measuring DO, pH, and conductivity each time I visit the vernal pool, in addition to surface area and depth of the vernal pools.  During these visits, I am surveying for larval amphibians, egg masses, and invertebrates.  So far we have seen many wood frogs, Jefferson’s salamanders, and spotted salamanders.  However, we seemed to skip “spring” this year and things warmed up very quickly.  Two vernal pools completely dried up! And the other two are getting very shallow!  We were able to add on another vernal pool to replace one that dried up, but things aren’t looking good for this year’s tadpoles and larval salamanders…  Next year, we will burn over the vernal pools and investigate changes in water chemistry and physical characteristics of each pool.

OLYMPUS DIGITAL CAMERA

A spotted salamander (Ambystoma maculatum) eggmass in one of the vernal ponds.

 

These salamander eggs are definitely ready for their close-up.

 

Working with one of the weather stations in a vernal pool (prior to the dramatic dry-down!)

Lastly, Mark Herr and I will begin a project looking at ecological trade-offs between thermal resource acquisition and predation at gestation sites of various sizes.  We will be deploying operative temperature models and foam predation models at 6 gestation sites (3 small and 3 large sites).  We will also radio track a couple gravid females at each site to determine body temperatures, survival, and lay dates.  For more on this project, see Herr’s post!  And for more on all of these projects, stay tuned to future posts!


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Don’t Prey on Me: Part 1

By Mark Herr

Imagine you’ve passed your deadline for filing a report at work. The report isn’t finished and now you need to decide where you’re going to finish it. This is critical, because your boss hasn’t confronted you about it yet, and you just might get off scot-free if you manage to get it in soon enough. Here is the dilemma: If you work from home, you won’t see your boss and so won’t get a thrashing. Without running into you, your boss might not even recall the fact that you were supposed to submit the report, and you’ll get off free and clear. Your job fully permits you to work from home, but unfortunately you don’t have access to all of the company resources you need to get it done as efficiently as possible. It might take twice as long to finish from home, and if your boss already knows it’s missing you are going to be in even more trouble if it’s extra late. If you go into the office you’ll be able to finish the report in half the time and might get it submitted before anyone realizes it’s missing, but you’ll also risk the thrashing from your boss if he is aware. This is the type of situation that people encounter all the time: problems with multiple solutions, each with positives and negatives and no clearly superior alternative.

It just so happens that scenarios like these are common in nature as well, and how organisms respond to problems like these has important impacts on ecology and evolution. When we discuss the ways that organisms respond to problems like these, we refer to them as trade-offs: situations where an individual, population, or species gives something up in return for something else. It seems simple enough, but it turns out that this concept is tremendously important. For example, if a predator inhabits a landscape with diminishing prey resources, it may face a trade-off in how to respond. Some individuals may become more active in order to find more prey to sustain themselves, while others may take the opposite route and stop moving in order to conserve what energy they do obtain. In this way, a trade-off like this could result in one species diverging into two – an active forager and an ambush hunter.

This brings me to the research project that I’m going to be working on this upcoming spring and summer. I’ll be working with lab post-doc Chris Howey, who’s currently studying the way that proscribed fire impacts Timber Rattlesnakes here in PA. Chris is particularly interested in the impacts that these fires have on gravid (pregnant) female rattlesnakes.

So while I’ll be working with Chris helping him out on his larger project, we’ll also conduct a side project on the trade-offs that gravid female rattlesnakes make during the active season. Shortly after emerging from their winter dens, gravid female rattlesnakes will congregate in open rocky areas to incubate their developing embryos. Typically they stay at these spots, termed gestation sites, for nearly the whole active season – until they give birth to live young sometime in late summer. They are spending their time thermoregulating in order to develop their embryos as efficiently as possible, so it’s obviously important for them to choose sites with good thermal qualities.

This is where they might encounter a trade-off, though. The largest, most open rocky areas will have the most sun exposure, and so one would think they would be the best places for the snakes to choose as gestation sites. However, we think that these sites might leave the rattlesnakes even more exposed to predators than they would be otherwise – this is especially important because the snakes are already more vulnerable while out basking than they would be if they were foraging in the forest where their camouflage is most effective.

This past summer we found that some pregnant females chose smaller, more closed canopy spots with less sun exposure as their summer gestation sites. Why would these rattlesnakes be choosing sites like this when big open sunny spots are available? We think that this might be a classic ecological trade-off: with snakes weighing the thermal quality of the spots with the risk of being attacked by predators.

Gadsden_Prey copy

This rattlesnake is doing a terrible job of trying to avoid predators.

This might be what’s going on, or it might not. Perhaps the snakes are just choosing the spots that are closest to where they denned up. Maybe the closed spots and the open spots don’t even have different predation risks attached to them! We’re interested in exploring this issue to see if this is really what’s going on, and understanding this dynamic might help conservation authorities understand the ways that a species under threat (like timber rattlesnakes here in the Northeast) use the different parts of their habitat.

In order to test to see whether a trade-off really is occurring, we’ll be assessing the different gestation spots chosen by rattlesnakes for their thermal qualities and predation risk. To test the thermal quality we’ll analyze the sun exposure of these sites and we’ll place thermal models designed to mimic rattlesnakes and analyze them against the preferred body temperatures of live rattlesnakes that we measure in the lab.

How will we measure predation risk? This is the part that I’m working on right now in preparation for this summer. We are making realistic foam rattlesnake models that we are going to set out at the different sites. The foam that we are casting the snakes in should hold the imprint of attack from the predators and should give us some idea of what type of predator went after our snakes! This is a technique that’s been used before (on rattlesnakes no less!) by Vincent Farallo to quantify the risk of predation, and we are excited to use it to test our hypothesis!

Making these foam models is taking up most of my time on this project right now, and we are going to need a couple hundred by the time spring starts, so I’m busy! I’ll post more updates on the project here on the Lizard Log in the future as we get rolling – but I’ll leave you off with some photos of the model making process that’s taking up my time now while there’s still snow on the ground!

The first step in making our models is to get an actual snake to cast them from! We took this preserved timber rattlesnake specimen from the teaching collection here at Penn State to make our mold for the future specimens.

The first step in making our models is to get an actual snake to cast them from! We took this preserved timber rattlesnake specimen from the teaching collection here at Penn State to make our mold for the future specimens.

Then we posed her in a typical basking rattlesnake position – getting the snake like that isn’t as easy as it seems! When specimens are fixed in formalin during the preservation process it tends to make them rigid and tough to work with, but we managed!

Then we posed her in a typical basking rattlesnake position – getting the snake like that isn’t as easy as it seems! When specimens are fixed in formalin during the preservation process it tends to make them rigid and tough to work with, but we managed!

After this we poured a rubber mold compound in the tray and let it set, then we removed the preserved snake and voila – snake mold!

After this we poured a rubber mold compound in the tray and let it set, then we removed the preserved snake and voila – snake mold!

Here you can see we’ve just poured the mixture into the mold – it will then quickly expand to fill the whole mold and once it hardens...

Here you can see we’ve just poured the mixture into the mold – it will then quickly expand to fill the whole mold and once it hardens…

We’ve got our rattlesnake model! The only step after this is painting it to make it look like an actual basking rattlesnake!

We’ve got our rattlesnake model! The only step after this is painting it to make it look like an actual basking rattlesnake!

Here’s a painted model, painting them is by far the most tedious part of the process – as the rattlesnakes have pretty intricate patterns. By the start of the project I’m going to need a couple hundred of these things painted and ready to go. It’s gonna be a busy semester!

Here’s a painted model; painting them is by far the most tedious part of the process, as the rattlesnakes have pretty intricate patterns. By the start of the project I’m going to need a couple hundred of these things painted and ready to go. It’s gonna be a busy semester!


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A Rattlesnake Summer

This past summer I began putting the pieces together for my 4 year project investigating the effects of prescribed fire on Timber Rattlesnakes.  The objectives of this project will be to determine how Timber Rattlesnakes are directly impacted by the fire and to determine how rattlesnakes are affected by changes within their environment which are caused by the fire.  This past summer’s objectives, however, were to basically get my feet wet, get to know the areas that may serve as potential study sites, get to know the focal species, and attempt to understand how to work with state agencies (SPOILER ALERT => this last objective would prove to be the most difficult).  It took awhile to get permits and all other paper work in line for the project, but all-in-all the summer was a great success because I identified 2 potential study sites (and possibly 2 more), I learned a great deal about these wonderful little creatures, and with the help of 2 great technicians (Rex Everett and Mark Herr) we came up with a couple great side projects.

Timber Marked

Male Timber Rattlesnake post-data collection. Note the painted rattle which allows us to identify it as a previous capture if we happen to stumble upon him later in the day. For all rattlesnakes we recorded basic morphometrics, sex, reproductive status, and marked the individual with a PIT tag which will allow us to identify it if captured much further down the road.

To date, we have identified two great study sites (and possibly more).  The first is located in Forbes State Forest and will be a rather large burn (a little over 600 acres!).  We’ve identified at least three potential gestation sites in this area, and although we were not able to spend a great deal of time down in Forbes, we know through talking with state foresters that there is a healthy population of Timber Rattlesnakes in the immediate area.  The actual area was nicknamed the “Snake Pit” by the district forester.  Aside from being a beautiful landscape, it is also the highest elevation within the state!  The “Snake Pit” is scheduled to burn in 2016 via an aerial ignition burn (dropping fire from helicopters!), which will provide me with a full pre-burn year to collect data in 2015 (Fantastic!).  In addition to Forbes, we also have a smaller prescribed burn planned for Rothrock State Forest.  We have visited this area quite frequently throughout the summer and we’ve captured a handful of Timber Rattlesnakes within the area as well (including one individual that we’ve radio-tracked to a den site).  The odd thing about this area is that all of the rattlesnakes we’ve captured thus far… have all been males of various ages.  Where are the females?!?  The presence of 1 year old males, however, suggests that the females are hanging out somewhere near by but we have not found where….  But, it leads us to question why we did not find any gravid females hanging out on the fantastic rocky slopes within the area?  Was this just a bad year for gravid females? Could the females be down in the valleys hunting chipmunks and gathering the energy needed for future reproductive bouts?

Gestation Site Paired

On the left, rising out of the thick ocean of Mt. Laural is a beautiful rock slab bathed in sunlight. This is fantastic gestation site. The large cap rock atop of the rock slab provides cover for the gravid females and refuge from high temperatures during the mid-afternoon and low temperatures at night. On the right, another type of gestation site is the large rock fields strewn out among Pennsylvania’s mountain sides. These gestation sites may be 100 m long and very open. Although this provides good thermal habitat for longer periods each day, would snakes be detected by predators more in this largely open area?

Throughout the summer we located close to 50 Timber Rattlesnakes.  Although we did not find gravid rattlesnakes at some potential study sites, we found many gravid rattlesnakes at other sites.  Sometimes these gravid rattlesnakes were in small areas that were about 10 m X 10 m (top left picture).  These smaller areas had all the essential habitat characteristics for a gestation site: an open canopy, rocks to lay out on, and rocks to hide underneath.  Other times, gravid rattlesnakes were found in large rock fields (top right picture).  Obviously the thermal environment would differ between these gestation sites.  Sun light would hit the more open rock fields early in the morning and last till much later in the day as compared to the smaller gestation sites surrounded by towering trees.  This may translate into the gravid Timber Rattlesnakes being able to maintain a preferred, optimal body temperature for a longer period of time each day within the more open rock fields.  Maintaining this optimal body temperature for a longer period of time each day may translate into more energy available for developing offspring and shorter gestation periods.  However, these more open areas may provide an advantage to visual predators such as hawks.  So would it be more beneficial for a gravid Timber Rattlesnake to gestate within a large open rock field despite the potential increased risk of encountering a predator?  To answer this question, a Penn State undergrad, Mark Herr, and I are putting together a side project for next summer where we will measure the thermal properties and predation intensity of these different types of gestation sites.  Additionally, we will radio-track gravid females at each gestation site in order to determine body temperatures maintained by individuals, duration of time spent at gestation sites, and date when females birthed young.  This should be a fantastic study! This past summer we began collecting preliminary data at a few gestation sites (using biophysical models) and found that operative temperatures at smaller gestation sites averaged 6 degrees C less than operative temperatures at large rock fields.  Additionally, this was a cooler summer than years past and only the gravid females at large rock fields birthed young at those gestation sites.  Gravid rattlesnakes from smaller gestation sites remained gravid as they traveled back to their den sites.  Most of these individuals appeared to return to their dens gravid, which likely means bad things for those potential young (i.e., mortality).

Mark and Neonate

On the left, Penn State undergrad, Mark Herr, collects habitat data at a smaller gestation site. Note the biophysical model in the foreground next to the backpack. These models will measure the operative temperatures for Timber Rattlesnakes, which are basically the potential body temperature of an individual if it was not thermoregulating (i.e., if it were conforming to the environment). On the right, a neonate Timber Rattlesnake hiding under a birch leaf (… that is a small leaf). Only at large, open gestation sites that maintained warmer operative temperature did we find neonates this summer.

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Gravid females from smaller gestation sites returned to their dens still gravid.  This likely spells disaster for the potential young.  Can you find the Timber Rattlesnake at this den?

Next spring we are ready to hit the ground running as snakes begin to emerge from their den sites.  In addition to the project’s main objectives, we are also prepping for a few side projects.  In addition to the project described above, I am also trying to understand why Timber Rattlesnakes choose one potential gestation site over another.  I will also be surveying and monitoring vernal pools within burn sites to determine how amphibians are affected by prescribed burning.  Stay tuned as we continue this project.  In addition to Mark, I also have one of the best Timber Rattlesnake expert in the state assisting me with this project: Rex Everett.  Together Rex, Mark, and myself are determined to make this project a success.  Additionally, we will be taking on at least two more technicians for next summer and any other undergrad interested in reptile ecology, thermal biology, and conservation.  For more information feel free to contact me at cah62@psu.edu.

Me and Timber1

The fearless leader collecting data on a Timber Rattlesnake found crossing the road at Rothrock State Forest.

Rex and Ratsnake

Rex Everett, snake expert, with a large Rat Snake found adjacent to the planned burn area at Rothrock State Forest