Penguin Poo Illustration: investigation of biophysics or fecal humor?

An interesting scientific illustration has been gaining some notoriety on the internet lately (nine years after it’s publication, I might add!). As I’m always singing the praises of what good scientific illustration can bring to science communication and public education, I thought I’d give this one some attention, too.

Now, don’t scoff at the subject of the investigation. What may very well sound like a silly study to you – investigating the pressure, viscosity and trajectory required to achieve the spectacular poop-shoot of penguins – may in fact be very important to the penguins themselves. (Never seen a penguin poop? Google it.) While even I may be more interested in the behavioral ecology of why penguins have evolved to shoot their poo quite so far (to avoid leaving the next exposed to predators, per chance? Or, to avoid soiling their feathers and thus spending energy cleaning them?), researchers Victor Meyer-Rochow and Jozsef Gal took a more experimental physics approach to the subject in their 2003 paper Pressures produced when penguins pooh – calculations on avian defaecation. published in the journal Polar Biology (click here for access to the full paper). Figure 1, as you can see below, really isn’t a great work of illustration necessarily, but it’s just gawktastic enough to be generating quasi-science stories on the internet for nearly a decade after it’s publication (it’s open access, by the way).

Fig. 1 Position of model penguin during defaecation and physical parameters used to calculate rectal pressure necessary to expel faecal material over a distance of 40 cm. From: Meyer-Rochow, V., & Gal, J. (2003). Pressures produced when penguins pooh – calculations on avian defaecation. Polar Biology, 27 (1), 56-58 DOI: 10.1007/s00300-003-0563-3

There was actually quite a fair bit of painstaking mathematical projections in the paper, estimating values for the viscosity fo the “semi-liquid” fluid, and consideration of, “non-Newtonian mechanisms of mucus participation, non-homogenous media inside the intestine, a certain amount of gut-wall elasticity, specific reflux zones, etc.” Indeed, many biomechanical and physiological cogitation was involved. What I think I find even more fascinating, however, is Figure 2, in which the authors present data to support their finding that, “the viscosity of penguin faeces lies between glycol and olive oil.” There’s even a handy comparison on the x-axes with auto tyre pressure:

Fig. 2 Rectal pressure (in Pa along left and mmHg along right ordinate) in relation to viscosity (abscissa) and three cloacal apertures (4.2 mm=rockhopper, 8.0 mm=Ade´lie, and 13.8 mm=gentoo penguin). The viscosity of penguin faeces lies between glycol and olive oil. For comparison, known viscosities of other substances are given along the abscissa. From: Meyer-Rochow, V., & Gal, J. (2003). Pressures produced when penguins pooh – calculations on avian defaecation. Polar Biology, 27 (1), 56-58 DOI: 10.1007/s00300-003-0563-3

Whether you can see it for the pure biophysics, or just needed something to lighten up your Wednesday, Meyer-Rochow and Gal have certainly illustrated the power of scientific illustration to capture our attention and posit on the oft neglected things in the study of life on Earth.