Yamanashi, Y., Bando, H., Matsunaga, M. et al. 2020. Development of bed-building behaviors in captive chimpanzees (Pan troglodytes): Implication for critical period hypothesis and captive management. Primates 61(5), 639-646.

Wild great apes build beds for sleeping by combining tree branches or other vegetation, but the development of this behavior is poorly understood. We investigated the development of bed-building behaviors by conducting complementary cross-sectional and longitudinal studies of captive chimpanzees. In the cross-sectional study, we created an ethogram of behaviors related to bed-building by observing 59 chimpanzees living at the Kumamoto Sanctuary, Kyoto University, and the Kyoto City Zoo. In the longitudinal study, we installed bed-building platforms, provided branches on the platforms on a regular basis, and recorded behaviors of five chimpanzees (including an infant born in 2013) over a 3-year period from February 2015 to February 2018 at the Kyoto City Zoo (total 490.7 h). We found that all the chimpanzees performed some form of bed-building behavior but wild-born chimpanzees possessed more sophisticated techniques than captive-born chimpanzees. We also found that although the offspring of a wild-born female only showed simple techniques at the beginning of the longitudinal study, his repertoire of bed-building behaviors became as complex as that of his mother by the age of five. Our results suggest that improved bed-building behaviors can be supported in captive-born great apes by providing learning opportunities during appropriate stages of development.