Spheniscidae – Penguins

The Spheniscidae or Penguins (order Sphenisciformes) are a group of aquatic, flightless birds. They live almost exclusively in the Southern Hemisphere, with only one species, the Galapagos Penguin, found north of the equator. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have evolved into flippers. Most penguins feed on krill, fish, squid and other forms of sea-life caught while swimming underwater. They spend about half of their lives on land and half in the oceans.

Although almost all penguin species are native to the Southern Hemisphere, they are not found only in cold climates, such as Antarctica. In fact, only a few species of penguin live so far south. Several species are found in the temperate zone, and one species, the Galápagos Penguin, lives near the equator.

The largest living species is the Emperor Penguin Aptenodytes forsteri: on average adults are about 1.1m tall and weigh 35kg or more. The smallest penguin species is the Little Blue Penguin Eudyptula minor, also known as the Fairy Penguin, which stands around 40cm tall and weighs 1kg. Among extant penguins, larger penguins inhabit colder regions, while smaller penguins are generally found in temperate or even tropical climates. Some prehistoric species attained enormous sizes, becoming as tall or as heavy as an adult human. These were not restricted to Antarctic regions; on the contrary, subantarctic regions harboured high diversity, and at least one giant penguin occurred in a region not quite 2,000km south of the equator, in a climate decidedly warmer than today.

Yellow-eyed Penguin Megadyptes antipodes – ©Bernard Spragg via Wikimedia Commons

Although almost all penguin species are native to the Southern Hemisphere, they are not found only in cold climates, such as Antarctica. In fact, only a few species of penguin actually live so far south. Several species live in the temperate zone; one, the Galápagos penguin, lives as far north as the Galápagos Islands, but this is only made possible by the cold, rich waters of the Antarctic Humboldt Current that flows around these islands.

Several authors have suggested that penguins are a good example of Bergmann’s Rule where larger bodied populations live at higher latitudes than smaller bodied populations. There is some disagreement about this, and several other authors have noted that there are fossil penguin species that contradict this hypothesis and that ocean currents and upwellings are likely to have had a greater effect on species diversity than latitude alone. Major populations of penguins are found in Antarctica, Argentina, Australia, Chile, New Zealand, and South Africa.

Macaroni Penguin Eudyptes chrysolophus – ©Butterfly voyages Serge Ouachée CC BY-SA 3.0 via Wikimedia Commons

Penguins for the most part breed in large colonies, the exceptions being the yellow-eyed and Fiordland species; these colonies may range in size from as few as 100 pairs for Gentoo penguins, to several hundred thousand in the case of King, Macaroni and Chinstrap penguins. Living in colonies results in a high level of social interaction between birds, which has led to a large repertoire of visual as well as vocal displays in all penguin species. Agonistic displays are those intended to confront or drive off, or alternately appease and avoid conflict with, other individuals.

They form monogamous pairs for a breeding season, though the rate the same pair re-couples vary drastically. Most penguins lay two eggs in a clutch, although the two largest species, the Emperor and the King penguins, lay only one. With the exception of the Emperor penguin, where the male does it all, all penguins share the incubation duties. These incubation shifts can last days and even weeks as one member of the pair feeds at sea.

Emperor Penguin Aptenodytes forsteri – ©lin padgham CC BY 2.0 via Wikimedia Commons

They generally only lay one brood; the exception is the Little Penguin, which can raise two or three broods in a season. Penguin eggs are smaller than any other bird species when compared proportionally to the weight of the parent birds; at 52g, the little penguin egg is 4.7% of its mothers’ weight, and the 450g emperor penguin egg is 2.3%. The relatively thick shell forms between 10% and 16% of the weight of a penguin egg, presumably to minimise the risk of breakage in an adverse nesting environment. The yolk, too, is large, and comprises 22–31% of the egg. Some yolk often remains when a chick is born, and is thought to help sustain the chick if the parents are delayed in returning with food.

When mothers lose a chick, they sometimes attempt to ‘steal’ another mother’s chick, usually unsuccessfully as other females in the vicinity assist the defending mother in keeping her chick. In some species, such as emperor penguins, young penguins assemble in large groups called crèches.