Penguins are fascinating creatures, waddling on ice floes until they get into the environment they seem more at home in, the sea. When they are incubating their eggs, they are reluctant to move from the spot for fear of exposing them to predators and to prevent a drop in the temperature necessary for the hatching process. Given this predisposition, you would think that when they get a call of nature, they would foul their nest to such an extent that it would turn in to a terrible mess. But not a bit of it.
Some penguins particularly the Adelie penguin, have developed a technique whereby through the use of gastrointestinal pressures they are able to propel their faeces sufficiently far enough away from the nest to maintain a clean and tidy environment for their brood to hatch in. For the enquiring mind, the obvious question is how much pressure do they deploy. Fortunately, a pair of scientists, Victor Benno Meyer-Rochow and Jozsef Gal, published a paper in the ever popular Polar Biology in 2003 entitled “Pressures produced when penguins poo – calculations on avian defecation” which reveals all.
The starting point in their examination of the problem was empirical observation. They noted that when a brooding penguin felt the urge to go, they would go to the edge of their nest with their rear facing the outside world, lift their tail and fire. So how to measure the pressures involved, particularly as penguins are protected species? The answer was to identify the key parameters required to make a calculation, namely the distance the faecal matter travels before it hits the ground, the density and viscosity of the material discharged and, finally, the shape, aperture and height above the ground of the penguin’s backside.
Travelling to Antarctica – hey, there is no point wrestling with these problems if you can’t get a field trip out of it – the two scientists carried out some field experiments. They noted that the expelled material hit the ground approximately 40 centimetres (with a standard deviation of plus or minus 12) away from the nest, leaving behind a whitish (if they had eaten fish) or pink (if their diet had been krill based) trail which ended a few centimetres from the nest’s periphery and which could be up to a centimetre wide. They also estimated that the penguin’s orifice had a maximum diameter of 8 millimetres at the point of firing and that its rear was 20 centimetres (plus or minus 6) above the ground.
The measurement of the viscosity of the material proved more challenging as results were inconsistent. However, they settled on a viscosity the equivalent of olive oil, a decision which provided them with all the parameters required to use the Hagan-Poiseuille equation for dynamic pressure – I’m sure you are familiar with it. The results revealed a pressure reading of between 10 and 60kPa, the process commencing with the higher pressure.
It is always useful, I find, in matters like this to have a comparative. When pressures on the rectal muscles in an upright human reach 55 mmHg, the external and internal sphincter relax and the contents of the rectum are expelled. During straining, pressures may rise to 100 mmHg. But these are paltry compared with the forces that the penguins muster.
The question of how a penguin chooses which direction to face when defecating wasn’t covered in the paper. That, of course, would require another field trip!