Though native to the southern polar regions of Earth, in particular Antarctica, some species can be found significantly further towards the equator.
Origin of the word penguin
Although still debated, the word penguin first appears in the 16th century as a synonym for great auk. When European explorers discovered what are today known as penguins in the Southern Hemisphere, they noticed their similar appearance to the great auk of the Northern Hemisphere, and named them after this bird, although they are not closely related.
From large to small species
The largest living species is the emperor penguin (Aptenodytes forsteri): on average adults are about 1.1 m (3 ft 7 in) tall and weigh 35 kg (77 lb) or more. The smallest penguin species is the little blue penguin (Eudyptula minor), also known as the fairy penguin, which stands around 40 cm (16 in) tall and weighs 1 kg (2.2 lb).
Among extant penguins, larger penguins inhabit colder regions, while smaller penguins are generally found in temperate or even tropical climates.
Eudyptes Vieillot, 1816
– crested penguins
Prehistoric penguins were much larger
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 around 2,000 km south of the equator 35 mya, in a climate decidedly warmer than today.
Penguins are counter shaded to help avoid underwater predators
All penguins are countershaded for camouflage – that is, they have black backs and wings with white fronts. A predator looking up from below (such as an orca or a leopard seal) has difficulty distinguishing between a white penguin belly and the reflective water surface. The dark plumage on their backs camouflages them from above.
Gentoo penguin swimming underwater at Nagasaki Penguin Aquarium. image: wikipedia/Ken FUNAKOSHI
How do they stay warm?
Penguins have a thick layer of insulating feathers that keeps them warm in water (heat loss in water is much greater than in air). The emperor penguin has the largest body mass of all penguins, which further reduces relative surface area and heat loss.
They also are able to control blood flow to their extremities, reducing the amount of blood that gets cold, but still keeping the extremities from freezing.
In the extreme cold of the Antarctic winter, the females are at sea fishing for food leaving the males to brave the weather by themselves. They often huddle together to keep warm and rotate positions to make sure that each penguin gets a turn in the center of the heat pack.
Physics suggests they would survive
Calculations of the heat loss and retention ability of marine endotherms suggest that most extant penguins would be too small to survive in such cold environments. However, in 2007, Thomas and Fordyce wrote about the "heterothermic loophole" that penguins utilize in order to survive in Antarctica.
Blood vessels with counter currents save them
All penguins living today, even those that live in warmer climates, have a counter-current heat exchanger called the humeral plexus. The flippers of penguins have at least three branches of the axillary artery, which allows cold blood to be heated by blood that has already been warmed and limits heat loss from the flippers. This system allows penguins to efficiently use their body heat and explains why such small animals can survive in the extreme cold.
Can they drink sea water?
Yes, they can drink salt water because their supraorbital gland filters excess salt from the bloodstream. The salt is excreted in a concentrated fluid from the nasal passages.
April 25th is #WorldPenguinDay
Source adapted from: Penguin. (2017, April 9). In Wikipedia, The Free Encyclopedia. Retrieved 09:46, April 26, 2017, from https://en.wikipedia.org/w/index.php?title=Penguin&oldid=774563531