Reaction to Novel Objects and Fecal Glucocorticoid Metabolite Levels in Two Species of Nocturnal Geckos

SIMPLE SUMMARY: Reptiles are commonly housed in zoos, wildlife parks or as pets, although there are many species for which welfare measures are not well established. Compared to mammals or birds, they have been under-researched, and, in this study, we focused on two of these species: crested geckos (Correlophus ciliatus) and leopard geckos (Eublepharis macularius). These geckos are nocturnal, and many questions remain unknown about their behavior or physiology indicators to properly implement welfare protocols. Here, we measured the reaction to novel objects and fecal glucocorticoid metabolite levels, trying to identify any relationship between them. Additionally, we assessed if some characteristic of the objects (e.g., color, shape, or smell) resulted in being more attractive to some species and/or individuals having the potential of being used as enrichment. No preference for any object was found and individuals which manipulated earlier and interacted longer with novel objects showed lower basal fecal glucocorticoid metabolite levels. Crested geckos had significantly greater and more variable fecal glucocorticoid metabolite levels than leopard geckos. These results can help to understand the reaction of geckos to novelty and have the potential to serve in their welfare assessment. ABSTRACT: Many reptiles are maintained in captivity and heavily traded, although welfare measures for many species are not well established and are under-researched compared to other animals. In this study, we focused on two of these species: crested geckos (Correlophus ciliatus) and leopard geckos (Eublepharis macularius). To better interpret their behavior in captivity, the individual reaction to novel objects and the fecal glucocorticoid metabolite levels were measured in an attempt to identify the potential correlation between them. Also, we explored if some characteristic of the objects (e.g., color, shape, or smell) resulted in being more attractive to some species and/or individuals. Equivalent responses to different objects were not obtained for all the geckos, the behavioral response being highly individual and context-dependent, although modulated by the species. Individuals which manipulated earlier and interacted longer with novel objects showed lower basal fecal corticosterone metabolite (FCM) levels. Differences according to the species suggested that crested geckos have significantly greater and more variable FCM levels than leopard geckos. Our results can help to understand the reaction of geckos to novelty and have the potential to serve in their welfare assessment, although more studies are needed to proper establish welfare protocols.