Hypothermia in foraging king penguins

The ability to dive for long periods increases with body size(1), but relative to the best human divers, marine birds and mammals of similar or even smaller size are outstanding performers. Most trained human divers can reach a little over 100 m in a single-breath dive lasting for 4 min (ref. 2), but king and emperor penguins (weighing about 12 and 30 kg, respectively) can dive to depths of 304 and 534 m for as long as 7.5 and 15.8 min, respectively(3-5). On the basis of their assumed metabolic rates, up to half of the dive durations were believed to exceed the aerobic dive limit, which is the time of submergence before all the oxygen stored in the body has been used up(4,6,7). But in penguins and many diving mammals(7,8), the short surface intervals between dives are not consistent with the recovery times associated with a switch to anaerobic metabolism(4). We show here that the abdominal temperature of king penguins may fall to as low as 11 degrees C during sustained deep diving. As these temperatures may be 10 to 20 degrees C below stomach temperature, cold ingested food cannot be the only cause of abdominal cooling. Thus, the slower metabolism of cooler tissues resulting from physiological adjustments associated with diving per se, could at least partly explain why penguins and possibly marine mammals can dive for such long durations.