Winter survivorship of hatchling painted turtles (Chrysemys picta) in Michigan
Roy D. Nagle1, Owen M. Kinney1,2, Justin D. Congdon1, and Christopher W. Beck1,2
River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA
Abstract: Hatchling painted turtles (Chrysemys picta) often exhibit delayed emergence by remaining in shallow subterranean nest cavities throughout winter. As a result, those at northern latitudes are sometimes exposed to lethal subzero temperatures. Our field study compared survivorship of hatchling C. picta during a winter in which low subzero temperatures coincided with the absence of insulating snow cover (1995-1996) with survivorship during the following three winters (1996-1997, 1997-1998, and 1998-1999), which were characterized by more moderate conditions. Ambient-air and soil temperatures were monitored at a weather station located within ~1 km of all nests. During the first winter of our study (1995-1996), minimum ambient-air temperature reached -25.6°C on 2 February, concomitantly with the complete absence of snow cover, and soil temperatures fell to between -7 and -9°C. Resultant overwinter hatchling mortality was 45%. Because some hatchlings survived temperatures well below the lethal limits described for freeze tolerance (-1 to -4°C), it is likely that hatchlings in Michigan sometimes survive by supercooling. During the following three winters, soil temperatures remained above -2°C, except during brief periods when they fell to -4°C in the absence of snow cover. Over-winter hatchling mortality was <3% during each of these last 3 years. Our study highlights the importance of insulating snow cover to survival of hatchling C. picta. Air temperature and snowfall data from southeastern Michigan over the past 33 years indicate that conditions associated with substantial winter mortality occurred in 3 out of 33 years (9.1%). We demonstrate that the impact of substantial over-winter mortality on hatchling recruitment is dependent on nest survivorship during the preceding nesting season.
SREL Reprint #2437
Nagle, R. D., O. M. Kinney, J. D. Congdon, and C. W. Beck. 2000. Winter survivorship of hatchling painted turtles (Chrysemys picta) in Michigan. Canadian Journal of Zoology 78:226-233.