One in a continuing series of posts highlighting the work of undergraduate researchers in the Langkilde Lab.
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.
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.
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:
- Adult and juvenile rattlesnakes will arrive to the den before neonates
- Predator visits will increase as more snakes begin to enter the den
- Snake activity in front of the den will increase positively with environmental temperature and decrease when temperatures drop, and
- 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.
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!