Penguin Species, Habitat, and Evolution
There are 17 species of penguin, some of which are found as far north as the equator, but only eight penguin species can be seen in Antarctica and the sub-Antarctic islands: chinstraps, emperors, Adélies, gentoos, kings, Magellanics, rockhoppers, and macaronis.
Scientists believe that around 40 – 50 million years ago, when Antarctica was breaking away from Gondwanaland, penguins formed their own species. They were originally native to warmer climates but had to adapt to the frozen region of Antarctica as they made their way south. Here are seven characteristics these polar penguins share across species.
1. Penguins Are Flightless Birds
Penguins are unique flightless seabirds that are at home on both land and sea. Unlike flying birds, which moult and replace their feathers slowly so they can remain airborne, penguins moult all at once over a period of 2 – 5 weeks during the summer.
This sudden moulting lets the birds head back out to sea without any “leaks” in their insulation. Moulting is an important process for the penguins, as their feathers wear out through the course of a year due to rubbing against other penguins, contact with the ground and water, and constant preening.
Once the moulting is done and new feathers appear, penguins are ready to head out to sea with a brand new coat.
2. Swimming Is a Penguin Talent
Over time, penguins have evolved their wings into flippers that enable them to zip through the water with ease. They have well-developed breast and wing muscles that help them push through dense water.
To make swimming easier, the penguin’s blood – the haemoglobin within it – has been adapted to transport large volumes of oxygen throughout the body while swimming.
Also, a large amount of myoglobin is in their muscle tissues, so they can store oxygen when underwater. While swimming, penguins like to tuck their heads near to their shoulders to keep their body compact.
They also keep their feet close to the tail, enabling them to navigate. Penguins have good eyesight underwater, and in fact the species’ vision is better suited to the water than the air.
Penguins can tell the difference between shades of blues, purples, and greens, and they have a secondary “see-through eyelid” to see clearly underwater.
3. Penguins Have an Open Diet
Penguins eat krill, which is a shrimp-like creature, as well as squids and fishes. For example, Adélie penguins, which can be seen in the Ross Sea, eat a variety of readily available high-energy food that is easy to gulp down.
During the summer months, penguins like to eat Antarctic silverfish, which are the most abundant small fish in the shallow coastal waters off Antarctica. Their shape is easy for penguins to swallow head first.
Meanwhile king and emperor penguins, a major wildlife attraction of Antarctica cruises, like to feed on lantern fish in addition to krill. Emperor penguins are particularly determined to catch food at great distances, known to forage anywhere from 164 – 1,454 km (102 – 903 miles) from their colony in a single hunting trip.
4. Large Colonies Are Preferred Penguin Breeding Grounds
On land, penguins form colonies that can contain up to a million nesting pairs. Adélie penguins in the Ross Sea migrate each spring from the outer pack ice towards land where they breed.
Most of the time spent travelling to their colonies is spent either walking, tobogganing, or swimming. The migration to the colonies is only done when the penguins have obtained a huge supply of body fat to sustain them while the southern ice pack is too thick to allow constant feeding.
They arrive at their breeding colonies in early October. The males are first to arrive, followed by the females. The colonies reach peak population around early November. It only takes them between one and 12 days to find a mate, and between one and three eggs are laid per breeding pair.
5. Penguins Drink Salty Water
Most penguins live in environments where there is little or no fresh water. They have either ice or saltwater to choose from when thirsty. With saltwater being more convenient and easier to obtain, penguins have a special adaptation that helps keep their salt levels balanced.
Penguins have a distinct supraorbital gland located near their eyes that filters salt out of their systems. As blood passes through the gland, it traps the salt before it can travel through the rest of their body. When the gland filters salt from the blood, the excess salt has to be expelled from the body.
Salt in the gland mixes with a small amount of moisture inside the gland before travelling down the nasal passage. Salty drops then drip out of the penguin’s nose.
Nonetheless, just because every penguin has this gland does not stop them from drinking freshwater when they can find it: Rockhopper penguins, which can be found on cruises to the Falkland Islands, prefer to live around freshwater sources rather than drink from the sea.
6. Research into Penguin Dives Reveals a Complex Biology
Emperor penguins can dive below the sea ice for up to 20 minutes at a time. To stay underwater that long, they have developed the ability to control how and when their muscles use oxygen. They can switch between two types of oxygen utility, either starving their muscles for oxygen or giving them a boost to keep them working during long dives.
To figure out how emperor penguins can dive for such lengths of time, scientists in McMurdo Sound designed special probes to monitor several penguins’ muscles during dives. In 50 recorded dives ranging between 7 – 64 metres deep (23 – 210 feet), the penguins stayed underwater anywhere from 2.3 – 11.4 minutes.
During the deeper dives, researchers found the penguins selectively sent extra oxygen from their blood into their muscles. They can only do this for short periods of time, however, until blood oxygen levels become too low for the rest of their body. When this occurs, penguins have to come back to the surface.
The downside of their oxygen-boosting adaptation is that it builds up lactic acid, so penguins will only do it if the prize (a good dinner) is worth it.
7. Penguin Feet Don’t Freeze on the Ice
Because most of the penguin’s body is warm and waterproof due to all their fat and feathers, they can easily overheat on a sunny day. To stay cool, heat escapes from their beak and feet, helping the body maintain a constant temperature.
However, this leaves their feet exposed to the cold. To stop their feet from freezing, penguins have special arteries in their legs that can adjust blood flow in response to foot temperature, enabling them to send just enough blood to their feet to keep them above freezing.
To make sure the heat isn’t lost, the warm blood on the way to their feet passes the blood that is coming back up, resulting in the warmer blood heating the colder blood before it continues down toward their feet.