Tokay geckos adjust their behaviour based on handler familiarity but according to context.

Animals need to recognize different individuals, both con- and heterospecifics, to make appropriate decisions. In the wild, responses to familiar individuals may vary depending on the context, which can be beneficial. However, differing responses towards human experimenters can influence experimental outcomes. Such effects might be particularly overlooked in reptiles which are frequently viewed as cognitively less advanced. We tested Tokay geckos' (Gekko gecko) ability to distinguish between familiar and unfamiliar handlers in two situations: in a novel situation (exerting physical constraint) and a routine situation (feeding from forceps as during regular husbandry). Geckos showed sex-specific differences towards familiar and unfamiliar handlers in a routine situation, but not in a novel situation, in which they showed individual repeatability. Our results further advance our understanding of reptile cognition revealing important insights into context specific responses in relation to handler identity with implications for experimental animal studies that are rarely considered.