A. Incubation
1. Incubation is the time spent warming the egg before it hatches. With the exception of emperor penguins, partners take turns incubating eggs, allowing each mate to leave to feed for several days at a time (Sparks and Soper, 1987).
2. A female emperor penguin transfers a single egg to the top of her mate's feet. The female goes to sea to feed while the male incubates the egg alone. She returns several weeks later, usually just before the egg is ready to hatch, to relieve her mate so that he may feed. The male fasts throughout the courtship, nesting, and incubation periods. He will live off reserves of body fat which may be 3 to 4 cm (1.2-1.6 in.) thick, losing up to 45% of his body weight (Marchant, 1990; Simpson, 1976).
3. The incubation period varies with species. It may be as short as one month, as in the erect-crested penguins, or as long as 62 to 66 days for the emperors (del Hoyo, et al., 1992).
4. The incubation temperature for penguins is approximately 36°C (96.5°F); it is a bit lower for the larger species. Emperor penguins can maintain an incubation temperature of 31°C (87.8°F) in an environment that is -60°C (-76°F) (Sparks and Soper, 1987; Brooke and Birkhead, 1991)
5. The greatest single cause for reproductive failure in some species is the mistiming between parents of nest relief during incubation. This usually occurs when the female fails to return from a foraging trip before the male deserts the nest (Ainley, et al., 1983). A male will spontaneously leave the nest and eggs when the motivation to feed overcomes that for incubating the eggs (Groscolas, 1990).
B. Hatching
Chicks first "pip" by poking a small hole in the egg. They then chip at the shell until they can push off the top. Chicks may take up to three days to chip their way out (Sparks and Soper, 1987).
C. Chicks at hatching
1. A fine down covers most newly hatched chicks. (King penguin chicks hatch naked and grow down within a few weeks.)
a. Down feathers of different species may be white, gray, black, or brown.
b. Down feathers are not waterproof, and chicks must remain out of the water until they acquire their juvenile plumage (Sparks and Soper, 1987). Adult plumage is acquired at about one year.
2. In all species, the coloration and markings of chicks separate them from adults. Scientists believe that adult penguins do not perceive the young birds as competitors for mates or nesting sites. The chicks'coloration may elicit parental behavior from the adults instead (Sparks and Soper, 1987).
Emperor chicks have striking facial markings.
3. The striking markings of emperor chicks may help to make the chicks more visible against the ice and snow; significant because emperors don't have individual nest sites where the young can be found (Sparks and Soper, 1987).
D. Care of the chicks
1 . Chicks require attentive parents for survival. Both parents feed the chick regurgitated food. Adults recognize and feed only their own chicks. Parents are able to identify their young by their chick's distinctive call (Marchant, 1990; Simpson, 1976).
2. Male emperor penguins exhibit a feature unique among penguins. If the chick hatches before the female returns, the male, despite his fasting, is able to produce and secrete a curdlike substance from his esophagus to feed the chick (Marchant, 1990; del Hoyo, et al., 1992) allowing for survival and growth for up to two weeks (Pr6vost and Vilter, 1963-1 Stonehouse, 1975).
A parent penguin feeds its chick regurgitated food.
3. Parents brood chicks (keep them warm) by covering them with their brood patch.
4. In some species, partially grown chicks gather in groups called creches. (Creche is a French word for crib.) (Simpson, 1976).
a. Creches provide some protection from predators and the elements (del Hoyo, et al., 1992).
b. Creches were once thought to be functional nurseries with adults providing protection and communal care. This has proven not to be the case since there is no feeding other than by parents (Simpson, 1976).
c. Temperate or subtropical crested penguins, like the macaroni or erect-crested, and penguins that nest in burrows, like the fairy or Humboldt, do not form creches (Sparks and Soper, 1987).
E. Chick development
A chick depends on its parents for survival between hatching and the growth of its waterproof feathers. This period may range from seven weeks for Adélie chicks, to 13 months for king chicks. Once a chick has fledged (replaced its juvenile down with waterproof feathers), it is able to enter the water and becomes independent of its parents (Sparks and Soper, 1987).
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