Adaptations

Swimming

Penguins 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.

Earlier estimates of swimming speeds were taken from observations of penguins swimming alongside moving ships, a method that proved to be unreliable.

• Emperors have been observed swimming 14.4 kph (8.9 mph), though they normally do not exceed 10.8 kph (6.7 mph.).
• King penguins have been recorded with a maximum swim speed of 12 kph (7.6 mph), although they typically swim from 6.5 to 7.9 kph (4 to 4.9 mph.).
• Adélie penguins probably reach maximum burst speeds of 30 to 40 kph (18.6 to 24.8 mph), but typically swim at about 7.9 kph (4.9 mph.). When swimming, an Adélie penguin can accelerate enough to leap as high as 3 m (9.8 ft.) out of the water onto an ice floe.
• Little penguins swim slower at about 2.5 kph (1.6 mph.).

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 paddle-like 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.

Having solid, dense bones helps penguins overcome buoyancy.

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.

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 to 6.2 mph.) and breathe about once a minute.
• 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.

Diving

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.

• Macaroni penguin dive depths typically range between 20 to 80 m (66 to 262 ft.) during the day and are usually less than 20 m (66 ft.) at night.
• Gentoo penguins can reach a maximum dive depth of 200 m (656 ft.) although dives are usually from 20 to 100 m (66 to 328 ft.).
• Adélie penguins have been recorded staying under water for nearly six minutes, although most dives are much shorter. They have been recorded diving to as deep as 170 m (558 ft.), although most dives are to less than 50 m (164 ft.).

• Chinstraps can reach depths of 121 m (397 ft.), but most dives are less than 50 m (164 ft.) Dives last from 30 seconds to 3 minutes.
• Most dives of king penguins last less than four to six minutes, although dives of up to eight minutes have been documented. The maximum recorded depth for a king penguin dive was 343 m (1,125 ft.).
• 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 565 m (1,854 ft.) The longest recorded dive for an emperor penguin was 27.6 minutes. Both of these measurements are considered extremes; most dives are between 21 to 40 m (70 to 31 ft.) of the surface and last 2 to 8 minutes.

Penguins mainly hunt prey in pelagic (open ocean) waters, however sparse evidence (such as stomach content analysis) suggests that gentoo, yellow-eyed, and emperor penguins dive and feed at the benthic (ocean floor) level as well. However, a detailed dive study of southern rockhoppers nesting/feeding off the coastal waters of the Kerguelen Archipelago suggest that benthic feeding is an important part of their diets.

• A group of 16 female southern rockhoppers were fitted with time-depth recorders (TDRs). In addition to performing traditional pelagic dives for food, these birds also dove regularly to highly consistent depths, indicating that they were hunting on the ocean's floor as well.
• The higher the amount of benthic dives recorded from a penguin, the greater the stomach content of the returning bird. This indicated that the benthic dives likely targeted high concentrations of crustaceans resting on the sea floor during the day. Pelagic dives averaged 53 seconds verses 66 seconds for benthic dives.
• Likely this behavior is rarely duplicated elsewhere since, unlike most known penguin breeding areas, the Kerguelen Archipelago features the presence of a shallow oceanic shelf where penguins can feed.

Synchronized diving has been seen for northern rockhopper and Adélie penguins. The behavior is poorly understood and observed only at the surface of the water, although individuals were fitted with time/depth recorders so additional underwater data was recorded and analyzed as part of these studies.

• A single pair of female northern rockhoppers observed in one study showed identical surface and depth dives hundreds of times straight during a period of seven hours. Their Euphausiid prey (Thysanoessa gregaria and Nematoscelis megalops) are known to form concentrated, dense swarms, suggesting that the rockhopper's synchronized efforts were likely a cooperative effort to increase foraging efficiency.
• Three pairs and one trio of Adélies were observed surface diving together in another study.
  • At the surface each small group would synchronously dive together, however, duration and diving depths underwater would vary. It is therefore assumed that no cooperative foraging took place underwater compared to the findings suggested previously in the northern rockhopper study.
  • The first Adélie to resurface would wait for their partner(s) to return to surface before repeating the behavior. Each group dove together 34 to 60 times over a period lasting 1.7 to 4.5 hours.
  • The krill prey in this particular area, E. superba and E. crystallorophias, generally form less dense swarms and distribute themselves over a wider depth range than the krill hunted in the northern rockhopper study. This may help explain the diving behavior differences between the two studies.
  • Leopard and Weddell seals are known to feed upon Adélies in this area. It is therefore believed that synchronously diving into the water at the surface is a behavior used to reduce the chances of predation.
  • A unique small-group feeding event of gentoo penguins was witnessed in 2006. A large flock of gentoos feeding on a swarm of krill separated into about 25 groups, each composed of 12 to 100 birds. Each separate group dove together, independent of the other groups. After one to two minutes underwater, individual members of a group would resurface. When all members of a particular group resurfaced, they would reform tightly together and repeat the behavior. The gentoos did not mix or interact with others outside their particular group during this feeding event.

During deep dives, the penguin heart rate slows.

• The heart rate of king penguins drops from 126 beats per minute (bpm) when resting at the surface between dives to about 87 bpm during dives.
• The heart rate of a diving emperor penguin is usually about 15% lower than its resting heart rate, which averages about 72 bpm. During one deep, 18-minute long dive, the emperor penguin's heart rate progressively slowed to 3 bpm, with a heart rate of 6 bpm for 5 minutes. However, the during the surface intervals between very deep and long dives, an emperor penguin's heart rate can increase to a maximum of 256 bpm, which likely aids in eliminating carbon dioxide and replenishing and reloading the penguin's oxygen stores in its tissues.

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.

Respiration

When swimming, penguins inhale and exhale rapidly at the surface. Just before a dive, penguins inhale and then dive on a breath of air.

Unlike diving marine mammals, penguins slightly inhale just before a dive.

• This increases oxygen stores, but makes the penguins more positively buoyant during a shallow dive and increases the risk of decompression sickness for deeper dives.
• A study on Adélie and king penguins showed that penguins can regulate their air intake before a dive, vigorously flap their flippers during the initial descent to overcome positive buoyancy, and then passively ascend from a dive using the expanding air volume in their body to conserve energy.
• Scientists believe that the deeper diving penguins, the king and emperor penguins, take in less air before diving while the other species make shorter, shallow dives and take in more air before a dive.

Salt Secretion

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.

Sleep

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.

Penguins living in the coldest regions have longer feathers and thicker body fat than those living in warmer regions.

Thermoregulation

The internal temperature range of penguins is 37.8°C to 38.9°C (100°F to 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. An emperor penguin can build up a 3 cm (1.2 in.) thick fat layer before the breeding season.

Penguins warm up by turning their dark colored backs to the sun.

One of the methods penguins use to conserve body heat is huddling.

The dark plumage of a penguin's dorsal surface absorbs heat from the Sun, which increases body temperature.

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.

During storms, emperor penguins huddle together to conserve. As many as 6,000 males will cluster while incubating eggs during the middle of the Antarctic winter. The penguins on the boundaries of the huddle continually move into the more sheltered interior, giving each penguin in the huddle equal access to warmth and benefit from 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 body heat.

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.