Diurnal basking (“sunning”) is common in many ectotherms and is generally thought to be a behavioural mechanism for thermoregulation. Recent studies have reported the occurrence of nocturnal basking in a few distantly-related species of freshwater turtles, but the true extent of this behaviour is unknown, and it may be underreported due to sampling biases (e.g., not surveying for turtles at night). Therefore, we initiated a global, collaborative effort to systematically document and quantify basking activity (diurnal and nocturnal) across a wide range of freshwater turtle species and locations. We conducted camera trap or manual surveys in North America, the Caribbean, Europe, Asia, Africa, the Seychelles, and Australia. We collected 873,111 trail camera photographs (25,273 hrs of search effort) and obtained data on 29 freshwater turtle species from seven families. Nocturnal basking was documented in 13 species, representing six families (Chelidae, Emydidae, Geoemydidae, Kinosternidae, Pelomedusidae, and Trionychidae), including representatives in Central America, Trinidad and Tobago, Africa, the Seychelles, Asia, and Australia. Nocturnal basking was restricted to tropical and sub-tropical locations, suggesting that environmental temperature plays a role in this behaviour. However, the primary factors driving nocturnal basking are yet to be determined and may vary geographically and by species. The frequency and duration of nocturnal basking varied among species and seasons, but nocturnal basking events were often substantially longer than diurnal events. This is the first study to document a widespread occurrence of nocturnal basking, and our results suggest that nocturnal basking may be a common, although overlooked, aspect of many species’ ecology.

The data were collected primarily from trail cameras set to time laps. Each author provided data from at least one (usually three) trail cameras that were deployed for (usually) at least two seasons. The raw data were presented as "counts" for all cameras (with the number of turtles of each species present in each photo reported), and "durations" for at least one camera (with the time of the first and last photo that an individual was in reported, so that durations of "basking events" could be recorded). R scripts were used to summarize those data per species per season per study site per day/night (all cameras combined) and per species per season per study site per hour (all cameras combined). Thus, if at a given site for a given season, three cameras were deployed for seven days each (and duration data were collected from each camera), then for each species detected on those cameras, the total number of basking events during the day and during the night (across all seven days and all three cameras) is reported, in addition to other summary statistics (likewise, those statistics are reported per hour).