Enlarge /. Bombs gone! When you approach a breeding penguin in its nest, it's best to watch out for flying droppings. According to a new study, Penguin Poo can travel up to 1.34 meters.
Nature is a brutal place, so chinstraps and Adélie penguins are reluctant to leave their eggs unguarded in the nest when hatching – even to relieve themselves. But you don't want to stain the nest with feces. Instead, a brooding penguin crouches, points its rear end away from the nest, lifts its tail and lets a fecal projectile fly – ensuring both the safety of the eggs and the cleanliness of the nest.
As early as 2003, two intrepid physicists were fascinated by this behavior and were inspired to calculate the answer to a burning question: How much pressure can these penguins generate to drive their feces off the edge of their nests? Answer: About three times more pressure than a human could generate. This paper earned them an Ig Nobel Prize in 2005 and lasting fame among those obsessed with pooping penguins. Now a couple of Japanese scientists have weighed the matter, calculated the projectile web of fecal matter expelled and recalculated the rectal pressure. These scientists reported their results in a draft that they had published in physics arXiv.
According to Victor Benno Meyer-Rochow from the Research Institute for Luminous Organisms in Japan, a co-author of the original paper from 2003, these faeces all started on an expedition that he led to the Antarctic. Although he collected samples of local seaworms and tiny land insects called springworms for further investigation, he also took numerous photos of the many penguins in the region that he used in his lectures. During a seminar at Kitasato University in Japan, a young woman asked about a slide on which a penguin was breeding in its nest and was amazed at the white and pink lines that shone outwards. She interpreted it as "decoration" and asked how the penguins had made it.
"I explained that a penguin gets up, moves to the edge of its nest, turns, lifts its tail, and then shoots from behind, leaving a 30-40 cm long strip of semi-liquid whitish substance," said Meyer-Rochow wrote in one Blog post from 2019. "Everyone laughed – except for the questioner. She blushed and sat quietly." (The color of the feces depends on the penguin's diet: if it is mainly fish, the poop is white. If the penguin has eaten krill, the poop takes on a pink hue.)
Meyer-Rochow claims that it was not a stupid question, especially since it prompted him to take a closer look at his slides, among which he found several photos depicting penguins in the middle of their droppings. Measuring the length of the strips that spread out from the nest was an easy thing. It was just as easy to estimate the height above the floor and the opening of the sewer – the opening through which penguins empty themselves. He also determined the "stickiness" of the surface of penguin manure. With this information, Meyer-Rochow and his co-author Jozsef Gal from the University of Loránd Eötvös in Hungary were able to calculate the force that would be required to drive the poop 30-40 centimeters. They then used this number to estimate how much pressure penguins would have to do to shoot their feces off the nest.
The answer: The internal penguin pressure can reach 10 to 60 kilopascals (0.1 to 0.6 atmospheres or 600 grams per square centimeter) and is therefore significantly higher than the pressure that the average person can exert when defecating. Meyer-Rochow said the pressure was comparable to "at least half the tire pressure of our cars" and added: "Not bad for a little guy who is a third the size of a person." However, the study did not investigate why the stripes radiate from the nest in all directions without any apparent preference. Does this depend on the wind direction or does a penguin somehow "choose" where to throw its droppings? That remains an unresolved question.
New things have come to light
In this latest article, Hiroyuki Tajima from Kochi University and Fumiya Fujisawa from Katsurahama Aquarium in Kochi, Japan state that the original paper from 2003 did not take into account the penguin droppings projectile. Instead, it focused on a horizontal distance. Tajima and Fujisawa argue that the ejection angle is not always horizontal, especially if the breeding environment is in a higher location – or if the penguin is standing on a rock, for example, when defecating.
Using Newton's equations, they calculated that Penguin Poo's maximum flight distance was 1.34 meters or 4.39 feet. Tajima and Fujisawa also re-examined the question of the rectal pressure required to achieve such a trajectory and found that it would be slightly higher than the original estimate. However, they found that their simplified equations did not take into account the hydrodynamics of feces in the air and in the stomach "which are left over for future work".
"Why these bombings sometimes embarrass zookeepers in breeding environments such as an aquarium," the authors wrote, why they decided to rethink the physics of penguin pooping. "It is practically important to know how far away their faeces are from the source. Such information would save animal keepers from the crisis. It would also be helpful if animal keepers were given instructions for new arrivals to avoid such an incident."
DOI: Polar Biology, 2003. 10.1007 / s00300-003-0563-3 (About DOIs).