A Low-Cost, Efficient, and Precise Technique to Quantify Key Life Cycle Events in Nests of Oviparous Reptiles
Phenological timing is of central interest to evolutionary ecologists because it is associated with fitness, but there has been limited study in animal groups with relatively secretive habits such as reptiles. This is especially true for the timing of hatchling behavior in wild reptile nests, likely attributable to few noninvasive methods for estimating parameters associated with egg hatching. We show that tri-axial accelerometers, small data loggers that measure rotation and inclination, can accurately quantify hatchling movement in wild reptile nests. In June 2018, we deployed an accelerometer in each of five freshly laid Snapping Turtle (Chelydra serpentina) nests in Algonquin Provincial Park, Ontario, Canada. In September 2018, nests were visited once daily to quantify the timing of hatchling emergence. The accelerometers worked as expected: there was statistically significant correspondence between the timing of accelerometer rotation in the nest (caused by movement of the hatchlings) and the timing of hatchling emergence. Furthermore, the number of hatchlings emerging from a nest was strongly and significantly correlated with the extent of accelerometer displacement. Our new technique allows new types of phenological data to be collected. It requires minimal effort and financial investment and thus is accessible to a broad range of research programs.Abstract
(A) Pendant G data logger. (B) Nest cage on the Sasajewun dam (Algonquin Provincial Park, Ontario, Canada) on a nest in a sandy soil with clear emergence hole forged by hatchling Snapping Turtles (C. serpentina). (C) A nest in rocky soil on the shoulder of a lightly traveled road.
Mean inclination (A) and inclination error (expressed as SD; B) in wild Snapping Turtle (C. serpentina) nests from Algonquin Provincial Park (Ontario, Canada) between days 175 and 235 (i.e., when no hatchling movement occurred) and in a laboratory study where the orientation of each of five Pendant G loggers was rotated twice daily. Circles are values from one Pendant G logger; thick horizonal lines are the means of all five loggers for each orientation. Orientation values (i.e., 1, 2, 3 on the X axis) represent a small sample of orientations tested in the lab, presented herein to demonstrate that estimation error in the accelerometers varies with orientation. “Wild (in lab)” represents the approximate orientation used in the wild. Note that “Wild (in lab)” and “Wild” have approximately the same inclination values (A) and similarly large estimation errors along the Z axis (B).
(A, C, E, G, I) Inclination of accelerometers (along the X, Y, and Z axes) in nests of wild Snapping Turtles (C. serpentina) from Algonquin Provincial Park (Ontario, Canada) from egg reburial to hatchling emergence. (B, D, F, H, J) Rolling variance (expressed in SD, scaled to a maximum of 1.0) of inclination calculated across all consecutive 24-h periods in each nest. Sample size (n) is the number of hatchlings emerged from each nest, and dashed line is the observed day of hatchling emergence. Panels on the right correspond to panels on the left-hand side of figure (e.g., A corresponds to B).
Relationships between inclination variance and characteristics associated with hatching for Snapping Turtle (C. serpentina) embryos from Algonquin Provincial Park (Ontario, Canada), with each circle representing data from a single accelerometer or nest. (A) The 24-h period in which maximum variance in inclination was observed closely was similar on the X axes and Y axes. (B) Observed day of hatchling emergence from the nest closely followed the mean day of maximum inclination variance in the nest. (C) Maximum inclination variance (expressed as the SD) recorded over a 24-h period (either on the X or Y axis) was greater when more hatchlings emerged from the nest.
Contributor Notes
