Penguins

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Adaptations for an Aquatic Environment

A. Swimming

1 .Some penguin species spend as much as 75% of their lives in the sea. Some species spend several months at a time at sea, only coming ashore for breeding and molting (del Hoyo, et al., 1992). The Fiordland crested penguins sometimes grow barnacles on their tails, an indication that they are at sea for long periods (Muller-Schwarze, 1984).

2. Swimming speeds generally are not well known (Kooyman, 1975). Earlier estimates of swimming speeds were taken from observations of penguins swimming alongside moving ships, a method that proved to be unreliable (Croxall and Davis, 1990). 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), Adélies at 7.9 kph (4.9 mph), and fairy penguins at 2.5 kph (1.6 mph) (del Hoyo, et al., 19921- Marchant, 1990).

3. To maintain streamlining with least resistance while swimming under water, a penguin keeps its head hunched into its shoulders. The feet are pressed close to the body against the tail to aid in steering (Marchant, 1990).

4. 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 the water (del Hoyo, et al., 1992). The wing and breast muscles are well developed, to propel the penguins through water, a medium much denser than air (del Hoyo, et al., 1992).

5. Having solid, dense bones helps penguins overcome buoyancy (Simpson, 1976).

6. Although it is more energy efficient for penguins to swim under water than at the water surface, they must come to the surface to breathe. They compromise by "porpoising" - leaping in and out of the water, like dolphins or porpoises (Sparks and Soper, 1987).

a. They are able to continue breathing without interrupting forward momentum. They can maintain a steady speed of 7 to 10 kph (4.3-6.2 mph). Porpoising also may confuse predators (Sparks and Soper, 1987; del Hoyo, et al., 1992).

b. Not all species exhibit porpoising. Emperors are not known to porpoise, and this behavior is infrequent in kings and members of the genus Spheniscus, but common in other penguins (del Hoyo, et al., 1992).

B. Diving

1. Most prey of penguins inhabit the upper water layers, so most penguins generally do not have to dive to great depths or for long periods (Moller-Schwarze, 1984).

a. Most species stay submerged less than a minute, but gentoo and Adélie penguins have been recorded staying under water for seven minutes (del Hoyo, et al., 1992).

b. Chinstraps can reach depths of 70 m (230 ft.), but most dives are less than 45 m (148 ft.). Nearly half are less than 10 m (33 ft.), and last between 20 and 30 seconds (Sparks and Soper, 1987).

2. Studies using radio tracking and automatic depth recorders reveal that emperor penguins sometimes hunt at great depths (Sparks and Soper, 1987).

a. Emperors hunt fast midwater squids and fishes and therefore tend to dive more deeply and remain submerged longer than other penguins (Sparks and Soper, 1987).

b. The deepest dive recorded for an emperor penguin was 535 m (1,755 ft.). The longest recorded dive for an emperor was 21 minutes. Both of these measurements are considered extremes; most dives are within 21 m (70 ft.) of the surface and last two to eight minutes. (Kooyman, pers. comm., Sparks and Soper, 1987; Simpson, 1976; del Hoyo, et al., 1992).

3. During deep dives, the penguin heart rate slows.

a. Adélie and gentoo penguins reduce their heart rate from 80 to 100 beats per minute (bpm) to about 20 bpm (Muller-Schwarze, 1984).

b. The heart rate of a diving emperor penguin is about 15% lower than its resting heart rate (Kooyman, 1992).

4. Under experimental diving conditions, penguins exhibit reduced peripheral blood flow (Scholander, 1940). The extent of blood redistribution during deep dives in penguins is still unknown (Ponganis and Kooyman, 1990).

C. Respiration

When swimming, penguins inhale and exhale rapidly at the surface (Simpson, 1976).

D. Salt secretion

Like other seabirds, penguins have glands in the bill 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 (Simpson, 1976).

E. Sleep

1 . A penguin sleeps with its bill tucked behind a flipper, which some sources believe serves no known purpose in penguins, but is a remnant of ancestral relations to flighted birds (Sparks and Soper, 1987). Other researchers believe the behavior may reduce the amount of heat lost through the face, particularly the nostrils (Campbell and Lack, 1985).

2. To conserve energy while fasting, penguins may increase the time they spend sleeping (Davis and Darby, 1990).

3. During the antarctic winter, when the period of darkness may last more than 20 hours, huddling emperor penguins incubating eggs may spend most of a 24-hour period sleeping (Groscolas, 1990).

To release excess heat, penguins may hold their flippers away from their bodies, so both surfaces of the flippers are exposed to air.

F. Thermoregulation

1 . The internal temperature range of penguins is 37.8°C to 38.9°C (100°F-102°F) (Simpson, 1976).

2. Overlapping feathers create a surface practically 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 shafts below the feathers trap air. This layer of air provides 80% to 84% of the thermal insulation for penguins (Muller-Schwarze, 1984; Sparks and Soper, 1987). The layer of trapped air is compressed during dives and can dissipate after prolonged diving. Penguins rearrange their feathers by preening (Moller-Schwarze, 1984).

3. To conserve heat, penguins may tuck in their flippers close to their bodies. They also may shiver to generate additional heat (Marchant, 1990).

4. 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 (Sparks and Soper, 1987).

5. Species in colder climates tend to have longer feathers and thicker fat than those in warmer climates (Simpson, 1976).

6. The dark plumage of a penguin's dorsal surface absorbs heat from the sun, which increases body temperature (del Hoyo, et al., 1992).

7. On land, king and emperor penguins tip up their feet, and rest their entire weight on the heels and tail, reducing contact with the icy surface (del Hoyo, et al., 1992).

8. Emperor penguins huddle together to conserve heat (Simpson, 1976). As many as 6,000 males will cluster while incubating eggs during the middle of the antarctic winter (Sparks and Soper, 1987).

9. Emperor penguins are able to recapture 80% of heat escaping in their breath through a complex heat exchange system in their nasal passages (Sparks and Soper, 1987).

10. On land, overheating may sometimes be a problem.

a. Penguins may prevent overheating by moving into shaded areas and by panting (Marchant, 1990).

b. Penguins can ruffle their feathers, breaking up the insulating air layer next to the skin and releasing heat (Sparks and Soper, 1987).

c. 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 (Sparks and Soper, 1987).

d. Temperate species, like the Humboldt and African penguins, lack feathers on their legs and have bare patches on their faces. Excess heat can dissipate through these areas (Sparks and Soper, 1987).

11. A penguin's circulatory system adjusts to conserve or release body heat to maintain body temperature.

a. 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 (Brooke and Birkhead, 1991).

b. 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 (Sparks and Soper, 1987).

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