Bulk stable isotope analysis of hair fails to reliably differentiate between wild chimpanzees with high and low meat consumption, as evidenced by inverse patterns in δ¹⁵N values where individuals with the highest meat intake exhibit average values and those with low intake exhibit the highest values.

When chimpanzees eat meat, their bodies don’t always store the nitrogen from it directly in hair. Instead, they recycle nitrogen from their own tissues, especially when food is scarce or during periods of stress, and this recycled nitrogen has a different chemical signature than the nitrogen from meat. So even if a chimp eats a lot of meat, its hair might show an average signal because most of the nitrogen in the hair came from its own body, not its diet. Meanwhile, a chimp that eats little meat but is breaking down its own muscle or organs for energy ends up with more of that recycled nitrogen in its hair, making the signal look like it came from a lot of meat.