A Long-Term Perspective of Delayed Emergence (aka Overwintering) in Hatchling Turtles: Some They Do and Some They Don't, and Some You Just Can't Tell

I re-examine the phenomenon of delayed timing of emergence from the nest by hatchling turtles (known as overwintering in temperate climates) within the context of the original summary of the topic in an article by Gibbons and Nelson in 1978. I base the overview on cumulative data from research at the Savannah River Ecology Laboratory since 1968 and reports from other locations during the past 34 yr. Investigators have reported known or suspected delayed emergence of hatchling turtles for 43 species, 22 genera, and 8 families from 11 countries and 36 U.S. states and Canadian provinces. The following perspective suggests questions to address and provides recommendations for how herpetologists should proceed in further investigating the phenomenon of hatchling emergence in turtles. The topic is one on which answers must be forthcoming to address turtle conservation on a global scale. For freshwater turtles, which include the majority of the world's turtles, natural selection has favored hatchlings that enter the aquatic habitat at the most propitious season for survival and subsequent growth. Nesting in most species spans several weeks; therefore, at the end of incubation hatchlings must use proximal environmental cues to adjust their timing of departure from the nest and entry into the aquatic habitat. Because of its widespread prevalence, delayed hatchling emergence in a turtle species should be considered the default behavior until evidence to the contrary is provided. Specifically, many turtles emerge several months after hatching, and in temperate climates emergence delayed by up to a year (overwintering) is likely the norm even though conventional wisdom predicts late summer or fall emergence.