Long-term Memory of a Complex Foraging Task in Monitor Lizards (Reptilia: Squamata: Varanidae)

Procedural memory allows animals to solve previously encountered tasks over weeks, months, or years efficiently. Although thoroughly documented in vertebrate clades such as mammals and birds, studies of procedural memory in squamate reptiles are lacking. Filling the gap in knowledge regarding procedural memory in squamates is important to understanding the degree to which procedural memory is unique to birds and mammals, as it is related to their unique cognitive abilities. We tested for memory of a problem-solving task in two species of monitor lizard (Varanus spp.) and a beaded lizard (Heloderma sp.) after a 20-mo hiatus in exposure, representing approximately 25% of their ages at the time of testing. All the monitor lizards had lower initial latencies to solve the task upon re-exposure posthiatus than they had as naive individuals during the prehiatus trials and reached minimum latencies in fewer trials than when previously tested. Our results indicate procedural memory of puzzle-solving behaviors on the time scales of years. Our results add to an emerging literature suggesting that squamate and other nonavian reptiles share a number of cognitive traits with birds and mammals, suggesting that such traits are far more widespread across taxa than previously recognized. We also discuss a framework for studying cognition in squamates that would allow tests of cognition across a great diversity of body forms and ecologies.