Long-Term Retention of Visual Tasks by Two Species of Emydid Turtles, Pseudemys nelsoni and Trachemys scripta Karen M. Davis and Gordon M. Burghardt University of Tennessee, Knoxville Long-lived species are expected to have long-term memory capabilities. In this study we tested nine Florida Red-bellied Cooters (Pseudemys nelsoni) on their retention for both a procedural food acquisition task and visual discrimination task learned in a previous experiment. The turtles were tested and retrained after two months, after another 7.5 months, and finally after 36 months of no interaction with the test apparatus during the intervening periods. Turtles retained memory for the choice task and needed little retraining throughout. Furthermore, in a different visual discrimination task, both P. nelsoni and Trachemys scripta turtles showed 100% retention after 3.5 months of no testing. Odor-controlled tests confirmed that turtles were using visual cues to solve the task. Thus, in a laboratory context turtles demonstrate long-term memory of visual discrimination tasks, which relates to apparent abilities in natural environments. Keywords: long-term retention, turtles, reptiles, learning, behavior As exemplified by many articles in this journal, the field of comparative cognition has reemphasized the need to study the behavioral plasticity and cognitive processes of a variety of ani- mals (e.g., Shettleworth, 2010). Although an increasingly diverse group of mammals, birds, and even fish are being studied (Laland, Brown, & Krause, 2003; Shettleworth, 2010), nonavian reptiles continue to be underrepresented in comparative cognition research (Davis & Burghardt, 2007; Lo ´pez et al., 2000, 2001; Wilkinson, Chan & Hall, 2007). In addition to being a phylogenetically important group (Riep- pel, 2008) that needs to be included in comparative cognitive studies, turtles are particularly advantageous subjects for investi- gations of long-term retention. First, turtles have sophisticated visual abilities and can be trained in many respondent and instru- mental tasks, especially those involving visual discrimination (Burghardt, 1977; Davis & Burghardt, 2007; Morlock, 1989). Second, most species of turtles are known for their longevity (Gibbons, 1987; Litzgus, 2006), and both freshwater (Freedberg, Ewert, Ridenhour, Neiman, & Nelson, 2005; Mitrus, 2006; Rowe, Coval, & Dugan, 2005) and sea turtles (Bowen et al., 1992; review in Lohmann, Luschi, & Hays, 2008) return to the same nest sites annually and some have shown nest site fidelity for up to 10 years. Furthermore, sea turtles show site fidelity to specific foraging areas (Broderick, Coyne, Fuller, Glen, & Godley, 2007; review in Lohmann et al., 2008). Thus, given these characteristics, turtle long-term memory needs to be studied experimentally. Animal memory studies have focused mainly on shorter reten- tion periods (30 seconds to 24 hours); these have demonstrated retention in rats, primates, birds, fish, and honeybees (review in Pearce, 2008). Turtle retention ability for a spatial task for up to 5 minute intertrial intervals has been recently noted by Wilkinson et al. (2007). Long-term retention measured in weeks, months, and years in nonhuman animals has been studied considerably less often than short-term memory (STM). The type of memory, length of reten- tion interval, and number of studies varies considerably among species. Experimental studies of learning and memory have dem- onstrated that rats remember conditioned shock stimuli for 90 days (Gleitman, 1971) and spatial stimuli for 21 days (Broadbent, Squire & Clark, 2007). Longer lived birds such as jay species can remember cache sites for up to 9 months which is related to their behavioral ecology since jays species differ in their retention capabilities with ecological factors (Balda & Kamil, 1992; Olson, Kamil & Balda, 1995). Territorial songbirds are capable of learn- ing to discriminate between individual neighbors’ songs and retain a memory of a neighbors’ song for at least 8 months (Godard, 1991). In a comparative study on long-term memory capacity for picture-response associations in pigeons and baboons, Fagot and Cook (2006), found that pigeons and baboons could memorize thousands of pictures when tested daily over 3–5 years. The Editor’s Note. Josep Call served as the action editor for this article.—JC This article was published Online First May 14, 2012. Karen M. Davis, Department of Ecology & Evolutionary Biology, University of Tennessee, Knoxville; Gordon M. Burghardt, Departments of Ecology & Evolutionary Biology and Psychology, University of Tennes- see, Knoxville. We thank Todd Freeberg, Julia Bartmess-LeVasseur, Carrie Branch, Sheri Browning, Jessica Owens, Ami Padget, Ellen Mahurin, and Ellen Harvey Williams, for constructive comments on earlier presentations and drafts of this article. Thanks also to undergraduates; Rachel Edwards, Julie Haskew, Erick Jenkins, Ruben Luna, Sara Myer, Jeff Orgain, Sara Young, and Lab Manager Catherine Smith in the Burghardt lab for help with testing and care of the turtles. This research was conducted under approved protocol numbers 222 & 1597 of the University of Tennessee Animal Care and Use Committee. Correspondence concerning this article should be addressed to Karen M. Davis, 569 Dabney Hall, Department of Ecology & Evolutionary Biology, University of Tennessee, Knoxville, TN 37996. E-mail: kdavis23@utk.edu Journal of Comparative Psychology © 2012 American Psychological Association 2012, Vol. 126, No. 3, 213–223 0735-7036/12/$12.00 DOI: 10.1037/a0027827 213