Adaptations for an Aquatic Environment
- Some penguin species spend as much as 75% of their lives in the sea. They may spend several months at a time at sea, only coming ashore for breeding and molting. The Fiordland crested penguins occasionally grow barnacles on their tails - an indication that they are at sea for long periods.
- Swimming speeds generally are not well known. Earlier estimates of swimming speeds were taken from observations of penguins swimming alongside moving ships, a method that proved to be unreliable. The fastest swimmers belong to the genus Aptenodytes. Emperors have been observed swimming 14.4 kph (8.9 mph), though they normally do not exceed 10.8 kph (6.7 mph). Both kings and chinstraps have been recorded at 8.6 kph (5.3 mph), Adélie penguins reach speeds of 7.9 kph (4.9 mph). Fairy penguins swim slower at about 2.5 kph (1.6 mph).
The heavy, stocky penguin body is poorly adapted for flying in air but
superbly adapted for movement through the water.
- A penguin hunches its head into its shoulders to maintain its streamlined shape and reduce drag while swimming. Its keeps its feet pressed close to the body against the tail to aid in steering.
- Penguin wings are paddlelike flippers used for swimming. The motion of the flippers resembles the wing movements of flying birds, giving penguins the appearance of flying through water. The wing and breast muscles are well developed, to propel penguins through water - a medium much denser than air.
Not only do they "fly" underwater, these Adélie penguins appear to
"fly" out of the water easily jumping 1.8 m (6 ft.) into the air. This
behavior is commonly seen when penguins come ashore onto
rough or high terrain such as ice floes and rocky shorelines.
- Having solid, dense bones helps penguins overcome buoyancy.
- Although it is more energy efficient for penguins to swim under water than at the water's surface, they must come to the surface to breathe. Many species of penguin porpoise - leap in and out of the water, like dolphins or porpoises.
- When porpoising, penguins can continue breathing without interrupting forward momentum. They maintain a steady speed of 7 to 10 kph (4.3-6.2 mph). Porpoising also may confuse underwater predators.
- Not all species exhibit this behavior. Emperor penguins are not known to porpoise and this behavior is infrequently seen in king penguins.
- Most prey of penguins inhabit the upper water layers, so penguins generally do not dive to great depths or for long periods.
- Most species stay submerged less than a minute.
- Gentoo and Adélie penguins have been recorded staying under water for seven minutes.
- Chinstraps can reach depths of 100 m (328 ft.), but most dives are less than 30 m (98 ft.). (Wilson and Peters 1999) Nearly half are less than 10 m (33 ft.), and last between 20 and 30 seconds.
- Most dives of king penguins last less than four to six minutes, although dives of nearly eight minutes have been documented. (Culik et al, 1996; Kooyman et al, 1992a, Kooyman et al, 1997) The maximum recorded depth for a king penguin dive was 304 m (997 ft.). (Kooyman et al 1992a)
- Studies using radio tracking and automatic depth recorders reveal that emperor penguins sometimes hunt at great depths.
- Emperors hunt fast midwater squids and fishes and therefore tend to dive more deeply and remain submerged longer than other penguins.
- The deepest dive recorded for an emperor penguin was 535 m (1,755 ft.). (Kooyman and Kooyman, 1995) The longest recorded dive for an emperor penguin was 22 minutes. (G. Robertson In Ponganis et al 1997) Both of these measurements are considered extremes; most dives are within 21 m (70 ft.) of the surface and last two to eight minutes.
- During deep dives, the penguin heart rate slows.
- Adélie and gentoo penguins reduce their heart rate from 80 to 100 beats per minute (bpm) to about 20 bpm.
- The heart rate of a diving emperor penguin is about 15% lower than its resting heart rate, which averages about 72 bpm. (Kooyman et al, 1992b)
- Under experimental diving conditions, penguins exhibit reduced peripheral blood flow.
- The temperatures of a penguin's peripheral areas (limbs and skin) drop during a dive while those of the core regions (heart, deep veins, and pectoral muscle) are maintained at the normal temperature. (Ponganis et al, 2001, 2003, 2004)
- When swimming, penguins inhale and exhale rapidly at the surface. Just before a dive, penguins inhale and then dive on a breath of air. (Kooyman et al, 1971)
- Penguins have glands under the eyes that help rid the body of excess salt. The secretion of salt and fluid often collect as droplets on the bill and are shaken off. These glands are so effective that penguins can drink sea water without ill effects.
Penguins excrete excess salt through glands located under their eyes.
- A penguin typically sleeps with its bill tucked behind a flipper, which some scientists believe serves no known purpose in penguins, but is a remnant of ancestral relations to flighted birds. Other researchers believe the behavior may reduce the amount of heat lost through the face, particularly the nostrils.
- To conserve energy while fasting, penguins may increase the time they spend sleeping.
- During the Antarctic winter, when the period of darkness may last more than 20 hours, huddling emperor penguins that are incubating eggs may sleep for most of a 24-hour period.
- The internal temperature range of penguins is 37.8°C to 38.9°C (100°F-102°F).
- Overlapping feathers create a surface nearly impenetrable to wind or water. Feathers provide waterproofing critical to penguins' survival in water that may be as cold as -2.2°C (28°F) in the Antarctic. Tufts of down on feather shafts trap air. This layer of air provides 80% to 84% of the thermal insulation for penguins. The layer of trapped air is compressed during dives and can dissipate after prolonged diving. Penguins rearrange their feathers by preening.
- To conserve heat, penguins may tuck in their flippers close to their bodies. They also may shiver to generate additional heat.
- A well defined fat layer improves insulation in cold water, but probably is not enough to keep body temperature stable at sea for long. Penguins must remain active while in water to generate body heat.
- Species in colder climates tend to have longer feathers and a thicker fat layer than those in warmer climates.
Penguins living in the coldest regions have longer feathers and thicker
body fat than those living in warmer regions.
- The dark plumage of a penguin's dorsal surface absorbs heat from the sun, which increases body temperature.
Penguins warm up by turning their dark colored backs to the sun.
- On land, king and emperor penguins tip up their feet, and rest their entire weight on their heels and tail, reducing contact with the icy surface.
- Emperor penguins huddle together to conserve heat. As many as 6,000 males will cluster while incubating eggs during the middle of the Antarctic winter.
One of the methods penguins use to conserve body heat is huddling.
- Emperor penguins are able to recapture 80% of heat escaping in their breath through a complex heat exchange system in their nasal passages.
- On land, overheating may sometimes be a problem.
- Penguins may prevent overheating by moving into shaded areas and by panting.
- Penguins can ruffle their feathers to break up the insulating layer of air next to the skin and release heat.
- If a penguin is too warm, it holds its flippers away from its body, so both surfaces of the flippers are exposed to air, releasing heat.
- Temperate species, like Humboldt and African penguins, lack feathers on their legs and have bare patches on their faces. Excess heat can dissipate through these unfeathered areas.
Penguins that live in warmer climates - like the Magellanic - have bare
patches of skin around the bill and eyes to help release excess
Penguins that live in cold climates - like the Adélie - have feathers covering most of their bills to help conserve body heat.
- A penguin's circulatory system adjusts to conserve or release body heat to maintain body temperature.
- To conserve heat, blood flowing to the flippers and legs transfers its heat to blood returning to the heart. This countercurrent heat exchange helps ensure that heat remains in the body.
- If the body becomes too warm, blood vessels in the skin dilate, bringing heat from within the body to the surface, where it is dissipated.