Physiological stresses imposed on penguins during diving can be great. Many other diving animals, such as the Weddell seal, are exceptionally adapted for very long, deep dives. However, penguins do not seem to be as well-adapted for diving as these mammals. For example, penguins have a lower oxygen capacity and blood volume than the Weddell seal…thus their capacity for sustained, deep dives is more limited (Stonehouse 1975).

The human world record-holder for a descent under water (assisted with weights and pulleys) has reached a depth of 133 meters, a feat that required the diver to hold his breath for longer than two minutes. However, most marine mammals can exceed that depth within their first few months of life. The most accomplished divers of all, elephant seals and sperm whales, sometimes dive to depths greater than one kilometer (Kooyman and Ponganis 2004). See Penguins as Diving Birds for more information on diving capabilities of penguins.

The three main physiological problems faced by diving birds include:

1) asphyxia during the dive (loss of oxygen accompanied by increase in carbon dioxide)

2) compressive effects of hydrostatic pressure

3) temperature regulation

These stresses can be reduced by limiting dives to short duration and shallow depths, and by leaving the water frequently. Most penguin dives are of this nature; however there are exceptions and sometimes it is necessary for penguins to remain in the water for long periods.