Fig. 1. Seasonal variation in soil moisture (A) and its relationship to body water content (B), plasma osmolality (C) and plasma osmolyte concentrations (D) in R. sylvatica inhabiting a semi-natural, outdoor enclosure. Data presented in A are weekly means ± S.E.M. of values recorded at 6-h intervals. Data presented in B-D are means ± S.E.M.(N=3-6 frogs per group); all response variables varied significantly (ANOVA, P<0.0001). In D, `+' denotes each day that frogs were likely to be frozen, given that T_e of a hibernating frog model was -0.4°C, the approximate equilibrium freezing/melting point of R. sylvatica tissues.