Latency in Problem Solving as Evidence for Learning in Varanid and Helodermatid Lizards, with Comments on Foraging Techniques

Cognition and learning have been widely studied in vertebrates, but not across much phylogenetic breadth. Non-avian reptiles, for example, have been poorly studied. Anecdotal observations and a few previous studies suggest that lizards may have strong cognitive skills owing, in part, to behaviors such as optimal foraging and territoriality. We tested four lizard species, including three species of monitor lizard (Varanus spp.) and one species of beaded lizard (Heloderma), in a longitudinal, repeated-trials experimental design using a puzzle-feeder device to evaluate learning, in the form of latency trends over time. We used a Bayesian multilevel modeling statistical method and incorporated unsuccessful trials as censored data. Collectively, all lizards showed a pattern of decreasing latencies over time. We interpret this pattern as learning among our lizards. Notable individual and inter-specific differences were evident, however, suggesting that learning abilities differed among the lizards. In this case, the monitor lizards exhibited steeper declines in latencies and greatly reduced inter-individual variation in comparison to the beaded lizards. Finally, we found differential use of the claws versus the snout among the lizards, which is consistent with a previously posed hypothesis based on different species than we measured.