Any air-breathing animal that dives must manage its oxygen stores with care. How emperor penguins manage their limited oxygen supply intrigues Paul Ponganis and his colleagues from the Scripps Institution of Oceanography. Travelling to Antarctica, Ponganis and his team fitted minute electrodes in either the aorta or vena cava of penguins, as well as ingeniously collecting blood samples from the birds while they were diving, to find out how they manage their oxygen stores while submerged(p. 217).

Analysing the diving birds' blood oxygen levels, the team realised that the birds shunt oxygenated blood from the arteries to the venous system (which usually carries deoxygenated blood), probably via the wings for oxygen storage prior to the dive. During the dive the birds absorb oxygen from the lungs, continue shunting oxygenated blood into the venous system to increase oxygen storage, and also appear to isolate muscle from the rest of their circulatory system. Using these strategies, the birds are able to maximise use of oxygen stored in the lungs, reduce their blood oxygen depletion rate by isolating muscle from the circulation and maximise pre-dive blood oxygen storage by shunting oxygenated arterial blood through the wings into the venous system.

Given that the diving penguins' muscle tissue is isolated from the animals'circulation, Ponganis suspects that the increase in lactate found in penguins at the surface after a dive that has exceeded their aerobic dive limit is caused by the release of lactate from the muscle where it accumulated during the dive.

Ponganis, P. J., Stockard, T. K, Meir, J. U., Williams, C. L.,Ponganis, K. V. and Howard, R. (
). O2 store management in diving emperor penguins.
J. Exp. Biol.