In my line of work, I deal with feces from a lot of different species. Never once, however, have I thought to model defecation pressure and distances.

Maybe I’m just strange.

A few years ago, German researchers felt the need to model the defecation habits of penguins. The title of the paper, published in Polar Biology, was “Pressures produced when penguins pooh – calculations on avian defaecation" (Meyer-Rochow et al 2003).

The authors considered the fact that penguins don’t leave their nests to defecate (probably preferring not to freeze every time they need to poop). Rather, they observed that penguins move to the edge, “stand up, turn their back nest-outward, bend forward, lift their tail, and shoot. The expelled material hits the ground maximally 40±12 cm away from the bird and then leaves behind a whitish or pinkish streak that can end a few centimetres from the nest’s periphery and may be up to 1 cm wide.

That observation lead (perhaps fostered by some alcohol?) to questions about the exit velocity of the feces.

Given their protected status, you can’t run around poking and prodding penguins, so much of the research is done from a distance. The researchers in this case used pictures to estimate the "aperture" and determined it to have a "maximal diameter of 8 mm at the moment of "firing"."

Using the size of the "exit" and an estimate of average penguin poop viscosity, along with the angle and distance of firing, they used mathematical models to determine the "penguin-generated pressures" associated with defecation.

I won’t get into all the of the calculations. Suffice it to say, the image at right will probably not been seen in too many other scientific papers.

They concluded that "fully grown chinstrap and Adelie penguins generate pressures between 10 kPa (77 mmHg) and 60 kPa (450 mmHg) during the evacuation of their faeces on land. The process of defaecation commences with the highest pressure initially and then rapidly drops to zero, hence the production of faecal streaks (and not ‘‘blobs’’). In water, different parameters would apply, although (as in air) the smaller the cloacal diameter, the higher the pressure."

And to wrap it up…

"All birds, penguins included, spend a considerable time preening and cleaning their feathers. It seems therefore that these birds propel their faeces as far away as possible (with a minimum amount of effort) lest they soil their plumage. Birds could theoretically increase their projectile defaecation range by squirting 45° up-wards. However, their upright posture and position of the vent prohibit this in penguins, but in eagles and other birds-of-prey the squirt is, indeed, directed upward by ca. 15–30° (unpublished observation). The forces involved apparently do not lead to an energetically wasteful turbulent flow. It is interesting to note that the streaks of the faecal material radiate from the edge of the nest into all directions (no preference is noticeable). Whether the bird deliberately chooses the direction into which it decides to expel its faeces or whether this depends on the direction from which the wind blows at the time of evacuation are questions that need to be addressed on another expedition to Antarctica."

Photo: Adelie penguins, Antarctica (credit: JHB Anderson)