Stable isotope ratios (δ¹⁵N and δ¹³C) in chimpanzee hair do not reliably correlate with the amount of meat consumed, as observed in two wild groups in Taï National Park, despite direct measurements of meat intake ranging from 12g to 26kg per individual over seven months, indicating that dietary protein sources cannot be accurately inferred from bulk hair isotopes in this population.

When chimpanzees eat meat or plants, the carbon and nitrogen in their food get broken down and mixed into the same pool of molecules used to build hair. Because the body uses the same pool for all proteins, no matter where the nutrients came from, the chemical signature in the hair ends up looking similar even if the diet changed a lot. This makes it impossible to tell how much meat was eaten just by looking at the hair's chemical markers.