Fig. 1. Normalized serum resorption (ICTP) and formation (PICP and osteocalcin) marker concentrations during the 3-month hibernation period. Each data point is the mean value from five bears. Serum was collected every 10 days; the first sample was taken December 31, the last was March 31. The resorption marker increased immediately after the onset of hibernation. After 10–20 days, the formation markers increased and appeared to remain coupled to the increased resorption for the duration of hibernation. The PICP and ICTP concentration values for the entire study period (i.e. pre-hibernation, hibernation and post-hibernation seasons) have previously been published (Donahue et al., 2003a).