|Sphenisciformes comprises one family (Spheniscidae), six genera, and 17 species.
Penguins are restricted to the Southern Hemisphere where they are oceanic or coastal denizens.
Penguins of the Antarctic and Sub Antarctic are oceanic and breed on coasts and pack ice. Species nearer the equator may be oceanic or inhabit inshore waters and breed in coastal or forest habitats.
Penguins are notable for their upright posture and stiff wings that cannot be folded against the body. Penguins are medium to large birds (1-40 kg; 40-115 cm) with a thick layer of fat beneath the skin. Adult plumage is blue-black or gray dorsally and white ventrally, sometimes with distinctive coloring or plumes on the head. Chicks are either entirely brown-gray, or white ventrally. Juveniles have adult-like plumage. Sexes are similar. Feathers are small and continuous (no feather tracts). Bills are long and often laterally compressed, holorhinal (nostril entire), impervious nares, and schizognathous palate. Penguins are flightless divers with poorly pneumatized skeleton, carinate sternum with two lateral notches, 15 cervical vertebrae and basipterygoid processes absent. Wings are modified as flippers (wing skeleton flattened and partially fused), base of wing has vascular rete (blood vessel configuration in which cooler blood returning to the body absorbs heat from blood flowing out to the wing), pectoral muscles are large, but biceps bracii absent (unique to penguins). Legs are short; placed far posterior on body; flat tarsometatarsus is incompletely fused; palmate feet with four forward pointing toes. Bilobed oil gland is tufted.
Galapagos Penguins (Spheniscus mendiculus) have been observed foraging with boobies, terns, and shearwaters.
Penguins dive well and use their flippers to swim underwater in pursuit of prey items. Prey items include anchovies, pilchards, cuttlefish, squid, and krill.
Predators of penguins include: humans, Leopard seals (Hydrurga leptonyx), Killer whales, sharks, stoats, rats (Rattus norvegicus), Weka (Gallirallus australis).
Hatching may be synchronous or asynchronous (one or two days apart). Often the younger of two chicks will not survive. Chicks are altricial and take 10-52 weeks to fledge. In some species chicks remain with and are regularly fed by adults until fledged. In other species the chicks may be fed till nearly adult size, then fast for several months while huddling with other chicks for warmth in a nursery. Average age of first reproduction differs between species, ranging from two to five years old. Life expectancy from fledging may be 20 years. Chicks have two nestling downs.
Penguins are considered monogamous and individuals often nest at the same nest site, with the same partner from the previous year. In some species, 13 year pairings have been observed. Courtship displays are varied and complex, and may include loud raucous vocalizations, 'mutual ecstatic displays'(mate recognition behaviors), and beak slapping (or bill-fencing displays).
Most penguins breed in large colonies, one of the largest being the Macaroni penguin colony in South Georgia, which is estimated to be five million pairs. Antarctic, sub-Arctic and cold temperate penguins breed in either spring or summer, whereas species in warmer climes have more continuous breeding seasons. Penguin nests range from shallow dishes of pebbles and vegetation, to holes dug in soft soil, to rocky depressions, to the space between the top of the feet and the pouch-like fold of abdominal skin. Nesting areas are diverse and include small caves, burrows, coastal forests, and pack ice. Females lay one to two whitish eggs per clutch, with two to four days between egg laying.
Overall, penguin males and females share the parental care duties, but incubation, brooding, and feeding-fasting cycles are diverse and complex. Some species begin fasting at the onset of the breeding season. In some species males and females share incubation, whereas in others incubation is primarily uniparental. Incubation duration ranges from 30-64 days, whereas parental incubation shifts may range from 5-64 days. Usually the male takes the first incubation shift after the female has laid the clutch. One of the longest incubation and fasting shifts occurs in the Emperor penguin. During the Antarctic winter, the female Emperor penguin lays one egg then departs to feed at sea. The male fasts while incubating for 60 days till the female returns at hatching time. At that point the female begins brood care while the male goes to feed at sea. Contrastingly, during the Antarctic summer the female Chinstrap penguin lays two eggs. The female then fasts while incubating for 30 days until the male returns from feeding at sea.
Some penguins waddle along shorelines and ice, whereas others hop from rock to rock. When on ice or snow, penguins can move swiftly by tobogganing (sliding along propelled by wings and feet). Penguins also use their modified wings as flippers to swim underwater. The Emperor penguin is an exceptional diver and can stay submerged for 18 minutes and dive as deep as 500 meters. Swimming speeds average two to three knots, but may reach 15-20 knots for short distances. Swimming often includes porpoising (repeatedly breaking the water's surface with enough momentum to lift the bird into the air for about one meter.)
Penguins are highly social, oftentimes breeding in large colonies. Some species forage cooperatively and may dive synchronously while foraging in small or large groups. Species that breed in large colonies often have elaborate visual and vocal displays.
Vocalizations are characterized as loud, short braying. In colonial species in which chicks group together in a nursery (or cr??che) recognition of mates and offspring seems based on individually distinguishable calls.
Historically penguins were hunted and boiled to extract oil from the heavy layer of fat beneath the skin. At the turn of the century, approximately 150,000 Royal penguins (Edypes schlegeli) were harvested each year for 20 years from Macquarie Island (located south of New Zealand). On islands off of the coasts of Peru and Chile, penguin eggs and guano (dry bird droppings) are collected for local use.
Twelve penguin species are included in the IUCN Red List of Threatened Species, three of those (Eudyptes sclateri, Megadytpes antipodes, Spheniscus mendiculus) are listed as Endangered. Major threats to wild populations include: hybridization, destruction of breeding habitat, human disturbance, egg and guano collection, predation by introduced mammals, commercial fishing, and oil spills.
Despite evidence derived from osteology, anatomy, behavior, histology, and protein comparisons, the evolutionary relationships of penguins remain elusive. Penguins have been considered related to loons (gaviids), grebes (podicepids), pelicans (pelicanids), and/ or tube-noses (procellariids). DNA hybridization places penguins within Cinconiiformes and estimates a close relationship between sphenicids, gaviids, frigatids, and tubenoses (procellariids).
At least eighteen penguin species are represented in the fossil record of the Southern Hemisphere and date back to the middle or late Eocene. A common ancestry for penguins and procellariids is suggested by the presence of tubular nostrils in fossil penguins and in the extant Little Penguin (Eudyptula minor).