The Need to Dive, the Need to Breathe
Penguins need to dive under water in order catch their food in the ocean. However, penguins need oxygen to breathe under water. For most species of penguins, the average underwater dive lasts 6 minutes, since most of their prey resides in the upper water levels. However, the Emperor Penguin feeds on squid, fish or krill that reside deep under water, so this species of penguin can hold its breath for up to 20 minutes. Emperor penguins are also known to dive up to 1,800 feet to find their prey. Another species, the Gentoo, is known to dive up to 500 feet. Unlike seals, penguins are relatively small, so their lungs can hold only so much oxygen. Also, underwater compression affects the penguins' lungs and air sacs. These crucial airways can only provide 1/3 of the necessary oxygen needed for each dive.
Adaptions to Effectively Use Oxygen
Research conducted on wild penguins in Antarctica shows some surprising adaptions in the penguin's blood and muscle tissues for increasing oxygen during an underwater dive. These penguins were fitted with special sensors to monitor their air level. Unlike humans, the ultra-sensitive hemoglobin present in the penguins' red blood cells allows the penguins to effectively utilize every last molecule of oxygen in their system for diving. The blood is sent mainly to the heart, brain and other major organs. Penguin hemoglobin is so effective that penguins can continue diving when other animals would suffer from severe tissue damage. In addition, the penguin's muscle tissues also helps it breathe efficiently under water. A penguin's muscle tissues can also store additional oxygen by using large amounts of the blood protein myoglobin. Also, a special enzyme allows the penguin's muscles to work without the presence of oxygen while neutralizing lactic acid buildup. When the penguins reach the surface and return to normal breathing, they can then expel this buildup of lactic acid. To further save on oxygen consumption, penguins can lower their heart rate to five beats per a minute. By using less energy, these birds are able to prolong their time diving under water.
Swimming and Breathing Near the Water's Surface
Penguins swim most efficiently in deeper water levels, but sometimes it may be necessary to swim at the water's surface. Some species of penguins use a breathing and swimming technique called porpoising, named after porpoises and dolphins. The birds come up for air, then inhale and exhale rapidly. They then start breathing without interrupting their movement forward. They leap in and out of the water. The penguins can maintain a speed of up to 6 mph while porpoising. However, this porpoising technique is not usually seen in King or Emperor penguins.