Nocturnal basking behavior in a freshwater turtle

The sight of aquatic turtles sunning themselves on exposed logs and rocks is common in many places throughout the world. This "aerial" or "atmospheric" basking behavior has been reported in numerous species and is an important component of turtle ecology, but observations of turtles "basking" out of the water are restricted almost entirely to daylight hours. To the best of our knowledge, there are only few anecdotal reports of "nocturnal basking" in freshwater turtles (Neil and Allen 1954, Boyer 1965), most recently from a single observation of several Lavarack's snapping turtles (Elseya lavarackorum) sitting out of the water at ~01:00 (Cann and Sadlier 2017). We have, however, repeatedly observed Krefft's river turtles (Emydura maquarii krefftii [sometimes considered its own species, E. krefftii]) in the Ross River (Queensland, Australia) exhibiting nocturnal basking behavior. Herein, we will describe our observations of this behavior and discuss hypotheses to explain it.