A. Food preferences and resources
1 . Penguins eat krill (a shrimplike crustacean in the family Euphausiidae), squids, and fishes. Various species of penguins have slightly different food preferences, which reduces competition among species.
2. The smaller penguin species of the Antarctic and the subantarctic primarily feed on krill and squids. Species found farther north tend to eat fishes (del Hoyo, et al., 1992).
3. Adélies feed primarily on small krill, while chinstraps forage for large krill (del Hoyo, et al., 1992).
4. Emperors and kings primarily eat fishes and squids (Kooyman, 1971).
Krill comprises a substantial portion of the diets of Antarctic and
subantarctic penguin species.
B. Food intake
1 . Intake varies with the quantity and variety of food available from different areas at different times of the year (del Hoyo, et al., 1992).
2. A colony of 5 million Adélies may eat nearly 8 million kg (17.6 million lb.) of krill and small fishes daily (Sparks and Soper, 1987).
C. Method of collecting and eating food
1 . Penguins feed at sea. Most feeding occurs within 15.3 to 18.3 m (50-60 ft.) of the surface. The location of prey can vary seasonally and even daily (del Hoyo, et al., 1992).
2. Penguins primarily rely on their vision while hunting (Marchant, 1990). It is not known how penguins locate prey in the darkness, at night, or at great depths, but some scientists hypothesize that penguins are helped by the fact that many oceanic squids, crustaceans, and fishes are bioluminescent (they produce light) (del Hoyo, et al., 1992).
3. Penguins catch prey with their bills and swallow it whole while swimming (del Hoyo, et al., 1992). Penguins have a spiny tongue and powerful jaws to grip slippery prey (Sparks and Soper, 1987; Brooke and Birkhead, 1991).
4. Different species travel various distances from the colony in search of food.
a. Hunting areas may range from 15 km (9 mi.) from the colony for Adélies to nearly 900 km (559 mi.) from the colony for king penguins (del Hoyo, et al., 1992). Emperor penguins may cover 164 to 1,454 km (102-903 mi.) in a single foraging trip (Ancel, et al., 1992).
b. Penguins walk and toboggan from feeding grounds to rookeries. When fishing grounds are far, penguins will feed in seal holes and other openings in the ice (Sparks and Soper, 1987; Marchant, 1990).
D. Fasting
1. Penguins go through annual fasting periods. Prior to fasting, penguins build a fat layer, which provides energy (Groscolas, 1990).
a. Penguins fast for prolonged periods during breeding seasons; they do not leave nesting areas to feed. Some penguins fast throughout the entire courtship, nesting, and incubation periods (Groscolas, 1990).
b. Penguins also fast during annual molting periods. The temporary reduction in insulation and waterproofing caused by the loss of feathers during a molt prohibits penguins from entering the water to feed (Sparks and Soper, 1987). Their fat layer provides energy until the molt is over (del Hoyo, et al., 1992).
c. Chicks fast near the time they are ready to shed juvenile feathers for adult plumage. Usually by this time, the parents no longer are feeding the chick. Growth stops during this fasting period, but resumes once the molt is complete.
2. The length of fasting depends on penguin species, sex, and type of fasting. The king and emperor penguins have the longest fasting periods.
a. Breeding male king penguins may fast for up to 54 days during courtship and the first incubation shift (Davis and Darby, 1990).
b. Breeding male emperor penguins may fast 90 to 120 days during courtship, breeding, and the entire incubation period (Davis and Darby, 1990).
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