Fiona Stewart was interested in knowing why great apes sleep in nests at night. There are a couple of hypotheses which have been floated regarding nest function: sleep quality, anti-predation, anti-parasite, and thermoregulation. To test these hypotheses, Stewart went out in Fongoli, Senegal and actually slept in nests that chimps had used the night before, in self-constructed replicas, and on the ground. She recorded data on sleep quality, the number of bug bites per hour of sleep, and recorded mean temperature at ground height and at nest height during the night. Results are published in a brief communication in AJPA.
The results are very preliminary, but her sleep was less disturbed in nests, she suffered fewer insect bites, and the nests appeared to provide some insulation from the cold. Perhaps the most telling result was in terms of sleep quality:
"All experimental nights’ sleep in this study were uncomfortable and characterized by low sleep quality (<0.50), compared with mean sleep quality recorded for captive chimpanzees (0.86) and human societies (Videan, 2006). "