Blanding's turtle hatchlings emerge from their natal nests naïve to environmental stimuli and primarily sense visual cues on the horizon as a dispersal target. During a period of hours or days, hatchlings develop a compass mechanism that allows them to maintain a direction of travel, even when the target is not visible. We examined the dispersal directions of Blanding's turtle hatchlings captured during dispersal by translocating them into a circular arena in a field of corn in order to measure their dispersal direction guided by a compass mechanism. To test for use of a sun compass, a magnetic compass, or both, we observed dispersal direction of hatchlings released at the center of the arena. Hatchlings were released in an initial trial, treated with normal (no-shift) or 6-hr clock-shifted photoperiods for 4 to 10 days, and released into the arena for a second trial with magnets (or non-magnetic controls) adhered to their carapaces. We predicted that clock-shifting would reduce dispersal angle 90° and disruption of magneto-reception would disorient hatchlings. All four treatment groups dispersed directionally during first trials (Rayleigh's Z-tests; all p < 0.001) and in second trials dispersal angles were unchanged in hatchlings with magnets (Watson's U2; both p > 0.50); they were not using a geo-magnetic compass. Hatchlings that were not clock-shifted maintained their initial heading but clock-shifted hatchlings reduced dispersal angle a mean of 111°, not significantly different than the experimental prediction of 90° (Rayleigh's Z = 22.217, p < 0.001, no-shift; Rayleigh's Z = 19.286, p < 0.001, shift; Watson's U255,58 p < 0.001). An analysis of dispersal angles using only daily means of groups of turtles each released on different days also showed significant directionality, no magnet effect, and a significant clock-shift effect (two-sample Hotelling test, p < 0.002). Hatchlings were using a sun compass exclusively.
John D. Krenz
Date of Degree
Master of Science (MS)
Science, Engineering and Technology
Schlenner, Meredith Anne, "Sun-Compass Orientation During Natal Dispersal in Hatchling Blanding's Turtles (Emydoidea blandingii)" (2015). All Theses, Dissertations, and Other Capstone Projects. 394.
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