What does an 800-pound gorilla eat? If you said: “anything it wants,” you’re not thinking like a scientist.

A scientist would say, “Let me analyze the isotopic composition of its excreta and I’ll get back to you.” Because a new study shows that the ratio of carbon isotopes found in mountain gorilla feces reveals how much fruit the apes have consumed. The scoop’s in the latest issue of the Proceedings of the National Academy of Sciences. [Scott A. Blumenthal et al., Detecting intraannual dietary variability in wild mountain gorillas by stable isotope analysis of feces]

Knowing what animals nosh on in the wild and how that diet fluctuates can offer a key to their health and the overall health of the species. But not all beasties like to dine al fresco, at least not where scientists can watch. So researchers decided to reach for the scat.

As a test case they focused on four mountain gorillas in a park in Uganda, because they could actually see what these apes ingested. Different plants have different ratios of carbon’s common isotopes. So for 10 months the researchers measured the carbon in the plants that went into the gorillas and then what came back out.

And they found that the dung don’t lie, at least when it comes to what’s been on Koko’s menu.

—Karen Hopkin

[The above text is a transcript of this podcast.]