King penguins (Aptenodytes patagonicus) live in the extreme environments of Antarctica. On land, they experience temperatures below -20˚C but are able to maintain surprisingly high core temperatures (~37˚C). At sea, staying warm is even more challenging, because penguins lose heat much faster in water than in air. This is because water has a much higher thermal conductivity than does air (meaning heat flows from the penguin's surface to water faster than to air because water is more dense and can store more heat).
From these insights, we know that king penguins will be the coldest, or most thermally stressed, when they are fishing in the water. How can they survive these harsh temperatures? Many sea mammals stay warm with insulating layers of thick fur or fat on their bodies. King penguins have both layers of fat and a dense coat of feathers. However, their fins and feet are more exposed. Their feet are naked, and their flippers have only short feathers. King penguins are adapted to let their flippers and feet -- their appendages -- remain colder than their main body -- their core. When swimming, they massively reduce the amount of blood going in and out of their appendages, a process called vasoconstriction, which makes their veins smaller so less blood goes through them. This reduces heat loss to the water and reduces heat exchange between the appendages and the penguin's core. This way, a penguin's cold feet and flippers don't send much cold blood back to their core body, which would cool down their core temperature.
King penguin veins are also structured so the warm blood from their heart passes close to the cold blood returning from their appendages. This warms the returning blood, reducing even further the cold blood coming into their core body. This is called counter-current heat exchange. Both adaptations can reduce heat loss to 2-6% of total heat loss compared to 19-48%.
Counter current heat exchange, using a dog paw as an example. We can see that without counter-current heat exchange (top), the blood coming from the paw to the core body (blue) is 16˚ by the time it gets back from the paw. However, with counter-current heat exchange, the blood coming from the paw to the core body (blue) is 36˚ by the time it gets back from the paw. A big improvement! This is possible by having the veins closer together, so the blood being sent from the warm core body warms up the returning blood.This is the same process penguin feet (and many cold-weather birds' feet) use to keep warm!
Q1: What is more important: appendage temperature or core body temperature? Why?
Q2: Summarize the adaptations and why they are important for king penguins in their habitat.
Hypothermia occurs when your internal temperature is too cold. King penguins, depending on how long they stay in cold waters, can become partially or fully hypothermic. A penguin is partially hypothermic if only its appendages are at a low temperature, but its core body is at a normal temperature. A penguin is fully hypothermic if its core body temperature is also low.
Penguins need to stay warm, but they sometimes are at risk of overheating — even in the Antarctic! When king penguins are active on land, they are generating extra metabolic heat and can risk overheating because their superb insulation (feathers, fat) reduces heat loss. However, a penguin's feet are naked, and its flippers have small feathers. Because their feet and flippers have limited insulation, they act as thermal windows, which are spots of a body where heat can be lost quickly. (You can think of thermal "windows" working like normal windows: open a window or close a window to let heat in or out). By controlling exposures of flippers and feet to the cold Antarctic air, king penguins can finely control heat loss and thus their internal body temperature.
Q3: How are king penguins able to control their core body temperature using their feet?
Q4: Why are penguin feet and flippers not more insulated to keep them warmer?
Q5: Note the differences in position between the thermal windows (flippers and feet) of these two penguins. Which penguin is warming up and which penguin is cooling down? What informs your decision?
An infrared camera can calculate the surface temperature of everything in the frame. The camera does this by using the radiation emitted by objects. It's important to note that it can only observe surface temperatures, and not the core temperatures of large mammals. You can learn more about how thermal cameras work on our Science page.
Researchers wanted to study how penguins warmed back up after long hunting trips in the sea. They decided to use thermal imaging cameras to study these processes. Due to a penguin's thick coat, the thermal camera cannot identify a penguin's core temperature, only its surface temperature. However, researchers could study how penguins thermoregulate using their flippers as thermal windows.
Researchers were particularly interested in these questions: Do penguins which are partially hypothermic warm up differently than penguins that are fully hypothermic? Do partially and fully hypothermic penguins stop vasoconstriction at different times when warming up?
Q6: What is your hypothesis?
Thermal images of a fully hypothermic king penguin flipper and chest (representing its core) as it rewarms after its return from the sea. At the upper left, you can see the time since it left the sea, the average flipper temperature, and the average chest temperature.
Q7: How do the temperatures of the flipper and chest differ at the beginning?
Q8: What is the last part of the penguin's body to warm? Why do you think this is?\
Mean (with standard error bars) temperature of king penguin flippers, as a function of time on land. Fully hypothermic birds are represented by filled squares and solid lines; partially hypothermic birds are represented by light squares and dashed lines.
(Note: Edited from original by removal of wild-colony and year-one lines.)
Q9: What differences do you notice between the fully and partially hypothermic populations?
The researchers found a 5-minute delay to flipper warming in fully hypothermic penguins. There is no delay to flipper warming in partially hypothermic penguins. Why might that be? One possibility is that core temperature warming took precedence over flipper warming. Researchers think that the hypothermic penguins continued to vasoconstrict their flippers to focus on raising their core (chest) temperature during the first 5 minutes represented in the graph. Then, once their core temperature was back to normal, they ended vasoconstriction to allow their flippers to begin warming.
Q10: Consider why king penguins would have adapted to warm up this way. What are the benefits of regaining a normal core temperature before regaining flipper temperature?
Researchers found that most of a penguin's body that is covered by thick feathers was, on average, 4 to 6 degrees Celsius colder than the air temperature. This is due to radiative cooling, which is when a warm object releases heat to the cold surrounding air.
One interesting example of radiative cooling, or night sky cooling, is the centuries-old practice of making ice in the desert. Peoples of North Africa, India, and Iran would pour shallow pools of water to leave out overnight. Even though the air temperature never went below freezing, the water still froze overnight due to night sky cooling!
Overnight, the penguins' feathers release heat to the cold sky through radiative cooling, leaving the outside of their feathers colder than the air temperature.
Q1: If the outside of their feathers are so cold, how do penguins stay warm enough? Why might losing more heat from cold feather coats ultimately allow penguins to retain more heat overall?
Luckily for the emperor penguins, their thick coats of feathers help them retain a higher internal temperature than the surface of their feather coats. You can see this with a thermal image: the penguin's eyes, feet, and flippers are closer to their internal temperature than their body. The amount of heat penguins lose to the air (via thermal convection) is determined by the temperature difference between the penguins' surface and the air. Heat flows from high to low temperatures, so the penguins' cold feather coats can allow them to gain a small amount of heat from the cold air.
Thermal image of two emperor penguins. The warmest spot in the image is the eyes, which are the most exposed part of their bodies.
Penguins are also facing the cold, strong polar winds.
Q2: Imagine you're on a windy beach with a group of friends. What might you do to stay warmer?
Along with their thick feathers, emperor penguins use huddling to warm themselves up!
Q3: How would huddling help penguins stay warm?
By pressing together, they reduce how exposed they are to cold air, which reduces the amount of heat carried away via thermal convection. They also block themselves from wind, which can accelerate heat being carried away during convection. Some penguins are on the outside of the huddle, which means they take the brunt of the wind.
Are you a teacher, student, or independent learner who went through this educational resource on penguins? Let us know how we did using the "Get in touch" button at your top right. We would love to hear how to improve our resources!