A comparative study of environmental factors that affect nesting in Australian and North American freshwater turtles

The timing of reproductive events is critical for fitness, and these events are often linked to weather and climate. Weather components are thought to influence the nesting behaviour of freshwater turtles, but to date there have been few quantitative studies and no comparative studies. We compared the environmental cues used by nesting Australian (Emydura macquarii and Chelodina expansa) and North American (Chrysemys picta) freshwater turtles, and quantified the differences in weather between days with and without nesting activity within the nesting season. We also characterized the diel time of nesting for each species. The results suggest that nesting behaviour is related to warm air and water temperatures in C. picta and to rainfall in E. macquarii and C. expansa. Chrysemys picta primarily nests in the afternoon and evening, E. macquarii is a crepuscular nester, and C. expansa nests diurnally. While changes in life history resulting from climate change are difficult to predict, we suggest that an increase in the number of El Niño events may have adverse effects on the two Australian species, whereas increases in environmental temperature may expand the number of nesting opportunities for C. picta.