Baby painted turtles (Chrysemys picta) are unlike the young of most other turtles, in that painted turtles hatch from their eggs in late summer or early autumn but seldom emerge from their nest until the following spring. Because the nest itself is shallow, turtles hatching at northerly localities presumably must survive exposure to freezing temperatures over the course of winter. Unfortunately, few measurements have been made of environmental conditions inside nests of painted turtles during winter, so the preceding statement is based largely on conjecture. A viable alternative explanation is that hatchlings survive only in nests situated in relatively warm micro- environments (e.g., beneath insulative snow cover, on south- facing hillsides) and that survivors emerging from nests in the spring have not been exposed to freezing temperatures. This research will be aimed at determining whether temperatures inside nests of painted turtles actually fall to levels in winter that are low enough to cause body fluids to freeze in other terrestrial vertebrates. If hatchlings do, indeed, survive exposure to low temperatures, later investigation will focus on whether survival depends on a capacity for animals to withstand supercooling or whether it is based on an ability for them to sustain partial freezing of body water. The research may ultimately demonstrate the existence of a unique physiological adaption to winter conditions.
