Background/Question/Methods Altered phenology of reproductive events has been noted as a particularly key indicator of biotic response to contemporary climate change. However, most research has focused on a single population of a given taxon (oftentimes at the edge of its geographic range), yet meta-analyses use such data as a proxy for the entire species. Moreover, few sufficiently long-term studies of phenology in reptilian taxa have been published. We address the possibility of climate-altered reproductive phenology with long-term (>10 years) data on nesting behavior in multiple populations of each of four genera of North American turtles (Kinosternon, Chelydra, Chrysemys, and Trachemys). Results/Conclusions We find that initiation of the nesting season has advanced significantly only in populations at the northern edge of the geographic range of a species. Populations located farther south within the geographic range of a species exhibited less marked temporal changes in nesting behavior. Our results appear to provide one explanation for the outcomes of meta-analyses that purport to exemplify the biotic impacts of climate change. We are now exploring what climatological variables explain the nesting patterns we observe in these turtles as well as testing whether the significant temporal shifts in phenology in populations at the northern edge of the range reflect phenotypic plasticity or adaptive evolutionary changes.