Chimpanzees primarily eat plant source foods, but like vertebrate prey due to high fat content; 91pct of observed consumption of sub-adult prey was head-first due to soft skull. With adults, with robust skulls, chimps wanted viscera first, probably to harvest the liver.

Meat Eating by Wild Chimpanzees (Pan troglodytes schweinfurthii): Effects of Prey Age on Carcass Consumption Sequence. Ian C. Gilby, Daniel Wawrzyniak. International Journal of Primatology, February 2018, Volume 39, Issue 1, pp 127–140. https://link.springer.com/article/10.1007/s10764-018-0019-9

Abstract: Despite the fact that many primates consume vertebrate prey, surprisingly little is known about the nutritional benefits of eating meat for members of this diverse order. Although chimpanzees (Pan troglodytes) primarily eat plant source foods, especially fruit, they consume vertebrate prey with excitement, attesting to its nutritional value. Meat is a concentrated source of macro- and micronutrients; however, a carcass is not a uniform package. For example, the mammalian brain has considerably higher fat content than lean muscle tissue. The brain both has great caloric value and contains high concentrations of long-chain polyunsaturated fatty acids, which are critical for normal brain function. It thus represents a large, nutrient-dense source of energy and essential nutrients that should be highly valued. We filmed consumption of 29 arboreal monkeys by chimpanzees at Gombe National Park, Tanzania, and recorded the order in which general regions of the body were consumed. Overall, the head was significantly more likely to be targeted first than either the torso (including viscera) or appendages. This result was driven by subadult prey, 91% of which were eaten head-first, probably because their skulls were relatively easy for chimpanzees to break with a single bite. Possessors of adult prey (with robust skulls) often first selected the viscera, probably to harvest the fat-rich liver, thus maximizing immediate return in the face of the threat of harassment or theft. This has important implications for our understanding of the nutritional benefits of meat eating among primates, and highlights the need for future studies that measure the nutritional content of specific tissues and examine which are preferentially consumed or shared.