Vertebrate Zoology: A Study Guide - T. A. Dauda 2014

Metazoans
Class Aves
Superorder Impennes - Order Sphenisciformes

There are about 15 known species of penguins. They are distributed throughout the Southern Hemisphere, primarily along the coast of Antarctica and adjacent islands. Outside the breeding season, they inhabit the open sea, usually well north of their breeding grounds, and are frequently found near the southern shores of Australia, Africa, and South America.

They are exceptional swimmers, though flightless. Their forelimbs are modified into flippers.

On land, penguins hold their bodies vertically because their legs are set far back. This posture is supported by a short, stiff tail, which serves as a prop when standing (Fig. 39). They walk with a slow gait, but can glide rapidly on their bellies by pushing off with all four limbs. The sternal keel is well developed, reflecting powerful pectoral Muscles that make up about 1/4 of the bird's body weight and enable the active use of the forelimbs in locomotion. Penguin feathers resemble scales due to their poorly developed barbs. They undergo a single annual molt, during which new feathers grow beneath the old ones, effectively pushing them out. Throughout the molting period, the birds remain on land and fast entirely.

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Fig. 39 King penguin with a chick

During the breeding season, penguins form pairs that may persist for life in most species (monogamy). When nesting, nearly all species form colonies numbering in the thousands, and frequently hundreds of thousands, of pairs. They build primitive nests, typically on rocky shores and less commonly on ice. The clutch contains 1-2, rarely 3 eggs. Both parents usually share incubation duties, though in rare cases only the male incubates. The non-incubating parent heads out to sea for 1-3 weeks to feed. After this extended foraging period, the partners switch roles. Many species possess a brood pouch—a fold of Skin on the abdomen—which the incubating bird uses to cover the eggs. Often, the eggs rest not in a nest, but directly on the bird's webbed feet.

Harsh Antarctic conditions are weathered thanks to a thick layer of subcutaneous fat, as well as the penguins' ability to huddle together in coordinated rotating circles moving in both clockwise and counter-clockwise directions. It is warm in the center of these formations and cooler on the periphery, prompting penguins on the outer edges to periodically shift inward while those on the inside move outward.

The largest of all penguins is the emperor penguin, standing 110-120 cm tall with a weight of up to 45 kg. Closely related is the king penguin, which reaches lengths of up to 96 cm. The most abundant and widely distributed species is the Adélie penguin. The macaroni penguin features distinctive tufts of golden feathers above its eyes. One of the smallest species is the Galapagos penguin, with a body length of up to 50 cm; it nests in the tropics, laying two eggs in rock crevices.

Penguins have no commercial value.