Assessing preferences of two zoo-housed Aldabran giant tortoises (Aldabrachelys gigantea) for three stimuli using a novel preference test.

Recent research has uncovered many complex cognitive traits and affective processes in many reptile species, such as the ability to make choices that are rewarding or pleasurable. The investigation herein was initiated after many years of anecdotal reports, and preliminary observations, that the two male Aldabran giant tortoises (Aldabrachelys gigantea), Wilbur and Little John, at Melbourne Zoo (Melbourne, Australia) would approach the fence-line of their enclosure, sometimes multiple times daily, to "solicit" interactions from zoo visitors and/or zoo staff. Following other research with Galapagos giant tortoises (Geochelone nigra), this experiment was a novel preference test with two male Aldabran giant tortoises to assess their individual preferences for three stimuli: (1) human interaction (shell and neck rubs provided using hands); (2) food (highly palatable carrot pieces); and (3) an "enrichment" ball (a red "boomer ball"). The results found that Wilbur highly preferred human interaction and food over the ball; whereas Little John preferred food, and showed some initial interest in the ball, but did not approach the human on any of his 13 human interaction trials. These results reflect previous published findings, that human interaction is a preferred "enrichment," but is dependent upon a multitude of other contextual factors, and is not preferred at all times by all individuals. Individual variation may be very important to understand to have greater positive effect on the welfare-related needs of each giant tortoise housed in captivity. Further research is clearly required to enhance the welfare and well-being of many types of zoo-housed reptiles.