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….

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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