Colin Carlson

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I am a first semester Honors junior in EEB, and I work with Tobias Landberg on a research project studying the behavior and morphology of the common snapping turtle (Chelydra serpentina), based on footage from a Crittercam project. The footage, collected over the summer, was from three turtles: Jawless and Lafayette from Wethersfield Cove, and Snippy from Shenipsit Lake. (see the snapping turtle research team page for the full story on the turtles). Also, for more information on Crittercam itself, visit National Geographic's Crittercam Homepage.

The purpose of this project is to analyze the behavior of the turtles based on the Crittercam data. This analysis encompasses the breath, dive, pausing, walking, and other aspects of locomotion of the three turtles.

Snapping Turtle Research: Fall 2008-Present

Background

Extensive research has been done on the locomotion of other turtles, ranging in size from box turtles to green sea turtles. Limb cycle frequencies in aquatic systems have been reported as reaching up to 2.70 Hz (cycle/s) in Chelonia mydas, 1.7 Hz in Mauremys caspica, 1.0 Hz in Chrysemys scripta and 1.39 Hz in Kinosternon subrubrum in one particular study (Davenport et al., 1984)[1]. More recent studies of terrestrial turtle locomotion have suggested that adult Chrysemys picta may reach speeds up to 1.605 Hz voluntarily, and when forced, can even reach 2.557 Hz (Zani & Clausen, 1994) [2].

Quantified Behaviors

To describe the turtles' behavior, I've classified the turtles' activity into six major behaviors: breathing, horizontal swimming, vertical swimming (up and down), underwater walking, and pausing. Breathing involves surfacing and projecting the tip of the head out of the water to breathe; the turtle does not, however, extend its entire neck out of the water. In Jawless, this behavior is typically prefaced by a bout of horizontal locomotion, in which the turtle simply moves at a constant depth through the water; in contrast, Snippy's breathing generally followed a vertical dive to the bottom of the water, a bout of horizontal locomotion along the bottom (possibly with "underwater walking" interspersed with swimming) and a vertical dive up to the surface of the water. Jawless demonstrated underwater walking relatively rarely, and Snippy only demonstrated two major bouts; while the turtles probably did walk more than it appears on camera, the limbs often aren't visible while the turtle is on the bottom, preventing us from telling whether the turtle is actually walking; in such situations, we assumed that the turtle was in fact swimming.

In order to analyze these behaviors quantitatively, other related factors were brought into play: for instance, the amount of time the turtle spent during one "bout" of a particular behavior (which was often reduced to the amount of time visible on the camera, due to unclear or murky footage) was a useful measurement that helped determine each individual turtle's most common behavior. Another more quantifiable analysis was of limb cycle frequency, which was measured as (number of cycles)/(time), or in short, cycles/s. A cycle was defined as a movement of the front right limb, followed by a movement of the front left limb.

Breath-Dive Analysis

Fig. 1: Breath duration histograms for the three turtles. From top to bottom, data collected from: Jawless, Lafayette, Snippy. Note that each graph is roughly centered at a different location.
Fig. 2: Dive duration histograms for the three turtles, in same order as Fig. 1.

The results of this analysis, which are summarized in Fig. 1 and 2, were different for all three of the turtles, yet there are shared trends in their breathing and diving behavior, and these trends indicate a relationship between these two behaviors.

Statistical analyses indicate a strong relationship between breath and dive duration, especially for Snippy. These factors of breath and dive duration ultimately go hand in hand. I have also statistically tested this fit, and found a strong positive correlation. The order of breaths relative to dives is not significant: the fits with dive length are equally significant for a breath and the preceding dive, and the breath and following dive. The lack of a difference is nevertheless an important result, as it indicates the turtles are neither "preparing for" or "recuperating from" dives. This is not to say these are not possible explanations for some of this behavior, but instead, the data is inconclusive as to whether these are in fact components of the turtle's breathing behavior.

Another important conclusion that could potentially be drawn from this data pertains to the influence of landscape on these turtles' behavior. For breath duration, which is summarized in Fig. 1, the three turtles were each slightly different, yet Jawless and Lafayette were more similar to eachother than to Snippy. This is also true of the distribution of dive durations for the three turtles, summarized in Fig. 2. A potential explanation of this difference is based on the depth of the water the turtles were inhabiting during the filming: whereas Jawless and Lafayette are in shallow water and so do not have to swim vertically as much as Snippy (who is in much deeper water), which may reduce the turtles' need to breathe longer breaths. Nevertheless, there are differences between Jawless and Lafayette, as turtles are like fingerprints: no two are exactly the same.

Pausing Behavior & Limb Frequency Cycles

The first stage of locomotion analysis in my snapping turtle research was a preliminary analysis of when the turtles paused, and when the turtles were locomoting. This analysis did not include when the turtle was breathing, and did not differentiate between different forms of locomotion. This analysis provided a framework for knowing when the turtles were pausing. The analysis was thus a preparatory step to simply get a sense for the overall behavior trends, before beginning the more specific and quantified analysis.

Fig. 3: Jawless Locomotion Data Over Time. Cycles per second are plotted over locomotion bout number. Note the negative trend.
Fig. 4: Time Plot, Breath and Dive Duration Over Time for Snippy (Blue Line = Dive Duration; Black Line = Breath Duration)

The major start to analyzing locomotion data came in recording limb frequency cycles for the three turtles. During continuous bouts of locomotion, the number of limb movements on one side (chosen to be the right side, which happens to be more visible in the footage) of the turtle (a logical proxy for the number of limb cycles) is recorded, as is the time duration of the bout. By dividing the movements into duration, a measure of cycles per second for limb cycle frequency is created. This is currently complete for Jawless and Snippy, and is underway for Lafayette.

Plotting the LCF variable over time (using locomotion bout number as a chronological proxy for time), there is clearly a negative trend in Jawless's limb cycle frequency (See Fig. 3). This suggests an escape response, with high initial locomotion rates that decline as the turtle "relaxes," or in more scientific (and accurate) terms, decreases its overall stress level in response to a lack of human intervention and adjustment to the context. The Snippy data does not suggest an escape response, as Snippy's behavior is relatively constant throughout the video. Lafayette, who ranks in inconsistency somewhere between Snippy and Jawless in this footage, may demonstrate an escape response, though the data analyzed so far is inconclusive.

Methods of Locomotion

Fig. 5: Bar Chart with Intervals for Snippy Locomotion. There is a significant difference between the LCF of horizontal swimming and all the other behaviors, but those other three behaviors are not significantly different.

For these turtles, there are different methods of locomotion that can be differentiated into four behaviors: moving horizontally, swimming up, swimming down, and walking. To monitor limb frequency cycles differing between these behaviors, every bout of locomotion was recorded with the kind of behavior as well as limb cycle frequency.

From an ANOVA it appears swimming horizontally for Snippy was significantly slower than swimming vertically (in either direction) and walking (Fig. 5). However, because Jawless is in shallower water most of his behaviors can only be classified as horizontal swimming, as he has less of an "opportunity" to engage in vertical swimming. Moreover, Jawless and Snippy both demonstrate little *visible* walking, but whereas Jawless is likely not engaging at all in this behavior, Snippy is likely walking with his limbs not visible, making it mostly impossible to document this behavior. Consequently, this allows the analysis to be possible for Snippy, but as most of Jawless' behavior is horizontal locomotion, an ANOVA-like test would not be possible or particularly relevant.

This analysis will soon be complete for Lafayette as well; however, I expect to see results that are very similar overall to Jawless' behavior, though perhaps with more walking behavior than for the other two turtles. However, it should be noted that predictions such as these are not particularly reliable, as the three turtles all demonstrate individual differences.

Current Analyses

Right now, I've finished analyzing breathing rates for all three turtles, a simple analysis of diving vs. pausing, and the data on limb locomotion rates for Jawless and Snippy. Although an analysis for Lafayette was attempted, unfortunately, Lafayette's footage does not show her limbs as much as would be necessary to complete an analysis, and so the locomotion data is restricted to the two turtles for which the limbs are visible. Consequently, analysis of the actual data is no longer "in progress." At this stage in the research, I am:

  1. Searching for explanations for breathing behavior based on the turtles' morphology.
  2. Comparing the two turtles' limb and breath cycles and the factors that may be relevant to each.
  3. Drawing conclusions about morphology's influence on behavior in these turtles (See section "Conclusions")
  4. Reviewing literature concerning the locomotion rates of other turtles. (See section "Background")

Labirintus3.jpg Questions or comments can be sent to Colin.Carlson@UConn.edu

Conclusions

References

  1. Davenport J, Munks SA, Oxford PJ. A comparison of the swimming of marine and freshwater turtles. Proceedings of the Royal Society of London.Series B, Biological Sciences 1984 Feb. 22;220(1221):447-75.
  2. Zani PA, Claussen DL. Voluntary and forced terrestrial locomotion in juvenile and adult painted turtles, chrysemys picta. Copeia 1994 May 16;1994(2):466-71.