Burghardt, G. M., Ward, B., Rosscoe, R. 1996. Problem of reptile play: Environmental enrichment and play behavior in a captive Nile soft‐shelled turtle, Trionyx triunguis. Zoo Biology 15(3), 223-238.

Giving captive animals the opportunity to interact with objects in a “playful” manner is often considered a method of environmental enrichment. However, the occurrence of play in nonavian reptiles is controversial and poorly documented. Similarly, the role of environmental enrichment in fostering psychological well‐being in reptiles has been little studied. For several years, an adult, long‐term captive, Nile soft‐shelled turtle, Trionyx triunguis, at the National Zoo (Washington, D.C.), was provided objects such as balls, sticks, and hoses in an attempt to reduce self‐mutilation behavior. The turtle spent considerable time with the objects, and the level of self‐mutilation behavior decreased greatly over many months. Video recordings made in various contexts were analyzed in detail, and an ethogram of this turtle's behavior was developed. The turtle interacted with the objects (e.g., basketball, hose, stick) for 20.7% of the time it was observed and was active for 67.7% of the time. Both figures are unusually high for any animal, especially a turtle. The relative lack of play in ectothermic reptiles is supported by the surplus resource theory of play, which considers the joint effects of parental care, metabolism, endothermy, and arousal in providing the context in which playfulness could be manifested and promoted in vertebrate evolution. The existence of vigorous playlike behavior in a member of an ancient reptilian lineage indicates that, in the right circumstances, object play can be performed by reptiles and that having the opportunity to do so may be beneficial in captivity.