In contrast, while on land during the ice-free season in western Hudson Bay, when ambient temperatures are considerably higher, polar bears limit their daily movements, remaining inactive for long periods (Knudson, 1978; Latour, 1981). However, they have been observed engaging in faster-paced pursuits after caribou and waterfowl (e.g. Brook and Richardson, 2002; Iles et al., 2013; LJG & RFR our unpublished data). In such cases, hyperthermia, rather than lack of profitability, may be a limiting factor to sustained activity for several reasons. Polar bears are typical of non-sprinting mammals in that almost all the heat produced during exercise is immediately dissipated and little is stored (Taylor et al., 1970; Best, 1982), making warmer ambient temperature conditions particularly problematic because they reduce the potential for heat dissipation during exercise. For example, 218–239 kg polar bears walking at 7.9 km/h reached their upper critical temperature (when core body temperature can no longer be regulated) at about −33°C. Furthermore, these captive bears could sustain this activity at temperatures only up to −20°C when allowed to ingest snow before returning to walk (Best, 1982).