Or why penguins in the cold Antarctic are more than twice as big as on the warm Galapagos Islands in South America

A biological information Text for children

---

Do you know emperor penguins? They are the largest and heaviest penguins in the world, measuring just over a meter tall and weighing up to 23 kg. With their majestic feathers, their graceful posture and their courageous character, they certainly deserve the name emperor penguins. In their home on the Antarctic coast in the southern hemisphere, the brave penguins have to endure temperatures of up to -13°F every day. In Germany it is comparatively warm in winter with an average of 35°F. 

Things are completely different for the Galapagos penguin, which lives on the warm, tropical Galapagos Islands, 1,000 km from the coast of Ecuador in South America. While the emperor penguin slides comfortably across the cold ice of Antarctica every day, the Galapagos penguin lets the sun shine on his stomach every day at an average of 84°F. This is also noticeable in the external appearance of the Galapagos penguin. At half a meter tall and weighing two to three kilograms, it is just half the size of the emperor penguin. 

But wait, what does temperature have to do with penguin body size, you ask? 

This is what the biologist Carl Bergmann asked himself in 1874 and derived Bergmann’s rule from his findings. Bergmann found that endothermic animals in colder climates are larger than their relatives in warmer climates. Endothermic animals can regulate their body temperature from the inside out. From a purely biological point of view, we humans also belong to the mammalian genus and, together with birds, are endothermic creatures. But why is that the case? 

To do this, we have to take a short detour into the world of physics and briefly look at the relationship between volume and surfaces. 

The ratio of body surface area to body volume of emperor penguins in cold climates is comparatively much smaller than that of the related Galapagos penguins in warm climates. This has a particular advantage for the penguins, because the emperor penguin loses less heat in the cold Antarctic and therefore does not have to freeze. The Galapagos penguins on their tropically warm island are happy when they can lose as much heat as possible and work up a sweat to cool down. That’s pretty cool, right?