Assessing colour preference in Aldabra giant tortoises (Geochelone gigantea)

Tortoises perceive different colours and rely on the visual system to find food. However, few studies have considered colour preference in tortoises, especially in land species. The aim of this study is to investigate whether Aldabra giant tortoises (Geochelone gigantea) housed in Parco Natura Viva (VR), an Italian zoological garden, show a specific colour preference in their social context. The study was divided into two different periods in which red and yellow balls of the same size were scattered around in the outdoor enclosure. In the first period, pieces of carrots were placed behind each ball whereas in the second period, carrots were replaced with apples. Data on the frequencies of interaction with red and yellow balls were collected. First, tortoises interacted more with the balls when pieces of apples rather than carrots were hidden behind them. No significant group-level colour preference was found; however, individual-level variation in colour preference was reported. In addition, tortoises interacted significantly more with the yellow balls in the second than in the first period. Food typology seems therefore to play an important role in determining colour preference in chelonians. Research aimed at identifying individual differences in animal preferences might be valuable to improve captive animal husbandry (e.g.: development of enrichment programmes, diets and rewards).