Lords of the Ice – How the Emperor Penguin Conquered the Antarctic
Survival in the Antarctic is testing compared to most of the planet. Life in this polar environment is sparse, and where it is found, it is highly adapted. The Emperor Penguin, Aptenodytes forsteri, is one of the few birds found in Antarctica, and is a species that pushes extreme adaptation to the limits. Antarctic conditions as far south as those colonised by Emperors (between 66oS and 77oS) can reach temperatures as low as -45oC and wind speeds of up to 5m/s are not unusual. Colonies, which can range in size from several hundred to several hundred thousand, are formed a considerable distance from the open ocean on sea ice, which provides a stable platform for the rookery – the breeding colony. This reproductive strategy has resulted in the development of a number of novel and often unique survival strategies that showcase the resilience and endurance of life on earth.
Fat, Feathers, Feet and Beaks –
The Emperor Penguin is the largest of all penguins, with adults reaching over a metre in height and weights of up to 40kg. This is nearly 30 times the weight of more tropical penguin species like the blue penguin found in South Australia. Polar fauna is often larger than more temperate counterparts. By increasing the size of the body, the surface area to volume ratio of an animal is increased. This results in less energy being needed to compensate for the heat lost to the environment, in turn allowing for a reduced metabolic rate. Keeping a low metabolic rate is essential for Emperor Penguins as they fast intermittently throughout the breeding season which can last for up to 1/3rd of the year, during which they rely on fat reserves built up by feeding on fish, crustaceans and cephalopods between January and March.
Emperor Penguins have optimised a number of more traditional avian features to increase survivability in a polar climate. Penguin feathers are far stiffer than normal feathers, are layered on top of each other like roof tiles, and are pressed very closely together over a layer of insulating down. It is estimated that the plumage of the Emperor Penguin accounts for 85% of its thermal resistance – an invaluable adaptation to have in the Antarctic climate. The feet of Emperor Penguins have a highly specialised vascular system that prevent too much heat being lost to the ice. The arteries that supply blood to the extremities are surrounded by the veins returning blood to the heart, forming a ‘Counter-Current Heat Exchange’. The warm blood flowing from the heart moves past the cooler returning blood, warming it. This prevents core temperatures from dropping as much as they otherwise might, and is highly effective – the returning blood is almost at body temperature by the time it reaches the heart again. The beak also employs a heat exchange system which has been shown to recover up to 83% of the heat that would otherwise be lost through breathing. At the same time water vapour is condensed on the walls of the nasal passageway and recycled. By reclaiming this water the penguins do not have to find fresh snow to eat as often, which requires leaving the relative warmth and safety of the colony.
Huddling and Incubation –
Emperor Penguins live in an unusual environment. This has resulted in the expression of a number of unusual behavioural choices which have been shown to be particular effective in assisting their survival.
The first, and most visually obvious of these, is mass huddling which can include as many as 6000 birds and has been observed from space. Many penguin species huddle, but the Emperor is unique in that it huddles even whilst incubating and rearing a chick – a time where other penguin species prefer to establish a defended territory. Huddling further reduces the surface area of the body that is exposed to the elements mentioned earlier. Whilst huddling the penguins move extremely slowly, taking small steps every 30 to 60 seconds. This slow movement allows penguins on the outside of the group to move inwards to more sheltered areas once they have had their turn in the colder, more exposed areas. Huddling has been shown to reduce energy expenditure of Emperors by up to 50% a day. Whilst in the rookery, Emperors reduce energy expenditure as much as possible. Along with slow movement, they rock back on their heels and prop themselves on their tail. This reduces their contact with the bare ice, helping to keep their metabolic rate low.
This rocking behaviour is also a key component of their incubation technique. Once the female lays an egg it is passed to the male. The female then leaves for the ocean to recover the energy used to produce the egg. She will later be able to identify her partner through vocalisations. The male places the egg on top of its feet, and a fold of skin on the stomach called a ‘brood pouch’ covers the egg. By incubating the egg without a nest the Emperor is able to continue moving while keeping the egg balanced in its feet. Parental investment in these chicks is extremely high, with rearing taking up to 13 months. During this period the male and female alternate duties, with one going to feed while the other cares for the chick at the rookery.
Emperor Penguins are true experts when it comes to survival in the Antarctic. By adapting typical bird features such as feathers and beaks to serve additional purposes they have been able to take advantage of a huge area of the planet with little to no competition. These phylogenetic changes have then been complimented by a number of behavioural techniques which increase not only the survivability of the individual, but also of the colony as a whole, and of generations to come. This level of adaptability is not seen often in nature, and together all of these factors have allowed the Emperor Penguin to become a true master of Antarctic survival.