Food Preferences and Resources
Penguins eat krill (a shrimp-like crustacean in the family Euphausiidae), squids, and fishes. Various species of penguins have slightly different food preferences, which reduce competition among species. (See Appendix for information on diet for each species.)
The smaller penguin species of the Antarctic and the subantarctic primarily feed on krill and squids. Species found farther north tend to eat fishes.
Adélie penguins feed primarily on small krill, while chinstraps forage for large krill.
Emperor and king penguins mainly eat fishes and squids.
Food Intake
Intake varies with the quantity and variety of food available from different areas at different times of the year.
The entire breeding population of Adélie penguins may consume as much as 1,500,000,000 kg (1,500,000 metric tons) of krill, 115,000,000 (115,000 metric tons) of fishes and 3,500,000 (3,500 metric tons) of squid each year.
Method of Collecting and Eating Food
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.
Penguins primarily rely on their vision while hunting. It is not known how penguins locate prey in the darkness, at night, or at great depths. Some scientists hypothesize that penguins are helped by the bioluminescence (light producing) capabilities of many oceanic squids, crustaceans, and fishes.
Penguins catch prey with their bills and swallow it whole while swimming. A penguin has a spiny tongue and powerful jaws to grip slippery prey.
Galápagos penguins have been observed participating in multispecies feedings with numerous types of seabirds including flightless cormorants (Campsohaelius harrisi, formerly Nannopterum harrisi), brown pelicans (Pelecanus occidentalis), brown noddies (Anous stolidus), blue-footed (Sula nebouxii) and masked boobies (Sula dactylatra), magnificent frigatebirds (Fregata magnificens), and Audubon shearwaters (Puffinus lhenninieri). Field observations indicate that pursuit-divers, such as Galápagos penguins and flightless cormorants, force prey animals to stay near the shore and surface of the water for a longer period of time, thus increasing the duration of these flocks.
Different species travel various distances from the colony in search of food.
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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. Emperor penguins may cover 164 to 1,454 km (102–903 mi.) in a single foraging trip.
- Antarctic penguins swim, walk, and toboggan from feeding grounds to rookeries. When fishing grounds are far away, penguins will feed in seal holes and other openings in the ice.
Conspicuous Band Markings
Fish predators (piscivores) are likely more effective at chasing and catching individuals, thus schooling fish may form dense aggregations as a defensive strategy against predators. In tests, schooling fish such as Cape anchovies are known to depolarize (break apart) when shown models with stripes compared to models without stripes.
Adult penguins in the genus Spheniscus have at least one black stripe around their bodies. It is believed that such a conspicuous marking may force individual prey fish away from the main school, potentially increasing the penguin's hunting efficiency.
The absence of such striping patterns in other penguin genera that do not concentrate on schooling fishes as part of their diet further supports this theory.
Stone Swallowing
One emperor was found to have 4.5 kg (10 lb.) of stones in its stomach contents. Stones have also been found in the stomach contents of Adélie, African, gentoo, Magellanic, and yellow-eyed penguins. Whether these stones were ingested by accident or not is unknown in these cases, however, king, rockhopper, and macaroni penguins have been clearly observed swallowing stones on purpose, sometimes in great numbers.
It's theorized that stones are swallowed to reduce buoyancy while diving or to alleviate the sensation of hunger. It's also believed that rockhopper and macaroni chicks swallow stones to aid in the digestion of tough exoskeletons of the crustaceans that play an important part of their diets.
King penguins in apparent good physical condition, breeding at Marion Island, were seen to purposely look for nearby stones. A single stone, approximately 10-mm to 30-mm in diameter, was selected at a time. The king would then throw its head back and allow the stone to be swallowed. The kings averaged swallowing six to 24 stones per minute, with one ingesting 31 stones in total.
Fasting
Penguins go through annual fasting periods. Prior to fasting, penguins build up a fat layer, which provides energy.
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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.
- 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. Their fat layer provides energy until the molt is over.
- 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.
The length of fasting depends on penguin species, sex, and type of fasting. The king and emperor penguins have the longest fasting periods.
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Breeding male king penguins may fast for up to 54 days during courtship and the first incubation shift.
- Breeding male emperor penguins may fast 90 to 120 days during courtship, breeding, and the entire incubation period.
