Fig. 1. Temperature profiles for representative nests at our study site in north-central Nebraska. Both nests contained eight painted turtles that were hatched in the laboratory and then placed into the nests in late October. (A) A relatively warm nest; (B) a relatively cold nest. The broken horizontal lines mark the equilibrium freezing point for bodily fluids of hatchlings (Storey et al., 1991; Packard and Packard, 1995; Costanzo et al., 2000b). Animals in this study hatched on substrates of vermiculite and consequently had a somewhat greater capacity for supercooling than turtles hatching in the field (Packard et al., 2001). Data are from Packard et al. (1997a).