A timber rattlesnake in classic ambush position, coiled, ready-to-strike, with head resting on fallen log.
Dissertation Research
| At the beginning of my dissertation, I felt that in order to more thoroughly understand the role of rattlesnakes in ecosystems I first needed to address more basic issues of foraging ecology, habitat use, and social structure. I began with a comprehensive analysis of timber rattlesnake food habits, dissecting over 1100 museum specimens from collections across the country and summarizing all dietary information from the literature (Clark, 2002). This effort allowed me to establish a strong pattern of geographic and ontogenetic variation in food habits, which served as a foundation for the rest of my dissertation. It also made me an expert in the indentification of half-digested mammal parts, so don't let anyone tell you that you can't get practical skills out of a PhD. |
A timber rattlesnake in classic ambush position, coiled, ready-to-strike, with head resting on fallen log. |
In the next stage of my research, I examined the development of prey recognition in a laboratory population of timber rattlesnakes. For these studies, I developed a new behavioral methodology, modifying techniques that had been developed for more active foragers (Clark, 2004a). I also found that timber rattlesnakes receive strong positive reinforcement from feeding events with very large prey, and modify their foraging behavior in subsequent trials accordingly. This learning behavior may be one of the mechanisms driving the widespread ecological pattern in snakes of ontogenetic shifts in diet towards larger prey as they grow (Clark 2004b). Additionaly laboratory research indicated that timber rattlesnakes could even use chemosensory cues from conspecifics to assess potential ambush sites (Clark, 2007). |
Click on the frame to see one of my "surveillance
videos" of a timber rattlesnake predation event. It is hard to see
any details, because the tapes were low-quality to begin with and lost
further resolution when they were digitized. Nevertheless, the yellowish
blur in the middle of the frame is a coiled snake. If you watch carefully
when the video plays, you will see a blurry red squirrel run in front
of the snake, get bit, released immediately and flee out of the frame.
All of this happens in about a second. Then the video speeds up and over
the next 10 minutes or so, the snake picks himself up, tries to locate
the scent trail of the bitten squirrel, leaves the frame, comes back and
tries again, and finally follows the scent trail out of the top of the
frame. I found this snake later that day with a sizeable meal bulge in
its midsection. |
However, as a field-oriented biologist, I feel that laboratory studies only establish the potential for important phenomena to exist in nature; in order for this potential to be fully realized, laboratory findings must be substantiated by field studies. The problem with studying rattlesnake predatory behavior in the field is that they sit in the same position for hours, or even days, waiting for prey to come within striking distance. Since direct observation of predatory behavior was not feasible, I developed inexpensive video monitoring systems using patched-together security equipment to create mobile, extended-time video recording devices that could collect data on prey encounters (Clark, 2006a). I used these devices to monitor free-ranging snakes implanted with miniature radio transmitters. This method allowed me to collect a wealth of ecological data, pertaining not only to foraging behavior, but also to other predator-prey interactions (Clark, 2005; 2006a; 2006b). |
| I made a lot of other interesting observations doing this fieldwork, but one of the more surprising was how gregarious these animals are. They frequently aggregated with conspecifics and exhibited correlated movements to different habitat features. These observations, along with various published reports indicating advanced sociality among rattlesnakes, led me to conduct a laboratory study on possible kin recognition in timber rattlesnakes. This study showed that captive-raised females do indeed recognize siblings, choosing to associate more closely with sisters than unrelated females (Clark, 2004c). |
A large group of gravid female timber rattlesnakes basking together at a site in northern Pennsylvania. Upwards of 30 females gave birth at this gestating area the year this photo was taken--by far the largest aggregation of rattlesnakes I have seen in the field. |
| This exciting result led me to hypothesize that the more gregarious rattlesnake species may live in family groups with a sophisticated social hierarchy. I am currently examining this idea as one part of a comprehensive study of genetic structure in timber rattlesnake populations. |
Undergraduate Research
 |
I first became interested in behavior, ecology, and herps as an undergrad at Utah State University. Under the tutelage of Dr. Edmund D. Brodie, Jr., I worked on a project on the flat-tailed horned lizard on the Marine Corps Air Station outside of Yuma, AZ. Some people think of the deserts of the southwest as ugly. I've always found them to be extremely beautiful, and chock full of interesting critters. We spent most of our time following lizards around with radio-telemetry and checking a pitfall trap array we had set up to inventory local diversity. |
We collected a lot of data on movements, habitat selection, and basic natural history that helped both the Marine Corps and the BLM to monitor the lizard populations more rigorously and make informed management decisions. We also discovered that the world's most appealing animal is a hatchling flat-tailed horned lizard (at right).All in all, it was an amazing experience, and sealed the deal as far as my career path went. I haven't looked back since. |
 |
 |
Home-Current Research-Past Projects-Publications -Curriculum Vitae -Prospective Students -Links |
