SREL Reprint #3478

Use of sun compass orientation during natal dispersal in Blanding's turtles: in situ field experiments with clock-shifting and disruption of magnetoreception

John D. Krenz1, Justin D. Congdon2,3, Meredith A. Schlenner1, Michael J. Pappas4, and Bruce J. Brecke5

1Department of Biological Sciences, Minnesota State University, Mankato, MN 56001, USA
2Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA
3Bar Boot Ranch, Box 1128, Douglas, AZ 85608, USA
443318 SE 150th Street, North Bend, WA 98045, USA
522675 County Boulevard 18, 58-A, Welch, MN 55089, USA

Abstract: When hatchling freshwater turtles emerge from nests and first experience environmental stimuli, they primarily use visual cues to disperse toward nearby open horizons or far dark horizons. Within hours, hatchling Blanding’s turtles (Emydoidea blandingii) develop compass mechanisms to maintain their headings when the initial dispersal targets become invisible. We captured hatchling Blanding’s turtles during dispersal in natural habitat, attached a magnetic or non-magnet disk to each turtle, translocated them into an arena in a visually uniform field of corn, and measured their compass orientation (heading). Hatchlings from the magnet and no-magnet groups were evenly divided into two environmental chambers (6-h clock-shift or non-clock-shift) to create four experimental treatments. After 5 to 11 days hatchlings were re-released in the arena. If hatchlings used a time-compensated sun compass, then clock-shifting would cause a ~90° change in heading. If they used a geomagnetic compass, disruption of magnetoreception would cause wandering. If both compasses were used simultaneously or sequentially, we predicted a range of outcomes. All four treatment groups dispersed directionally during both trials, maintaining their prior headings in natural habitat except for the clock-shift treatment which changed heading ~90° as predicted. The ability of hatchlings to maintain prior headings despite the disruption of geomagnetism supports the absence, inactivity, or disregard of a geomagnetic compass. Only a time-compensated sun compass coupled with an internal clock was necessary and sufficient for hatchlings to maintain compass headings during natal dispersal when relocated from natural prairie habitat to a monoculture habitat with a relatively uniform visual horizon.

Keywords: Biological clock; Clock-shift; Geomagnetic compass; Natal dispersal; Orientation; Sun compass

SREL Reprint #3478

Krenz, J. D., J. D. Congdon, M. A. Schlenner, M. J. Pappas, and B. J. Brecke. 2018. Use of sun compass orientation during natal dispersal in Blanding's turtles: in situ field experiments with clock-shifting and disruption of magnetoreception. Behavioral Ecology and Sociobiology 72(11): Article 177.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).