We recently completed a study to answer that question. As it turns out, river otters do a lot at latrines. They groom themselves, they groom each other, sniff things, dig and wrestle. Sometimes they visit in groups but more often they visit a latrine on their own. We developed and used a behavioral ethogram to describe behaviors that river otters display at latrines. We used trail cameras to capture river otter behavior and used that information to determine the most common behaviors, group size, time of day that otters prefer to visit latrines and visitation rates over the course of a year.
Check out the full study here! Be sure to look at the supplementary information where you can view actual video footage of each river otter behavior type (for example, look at this video of river otters wrestling!).
A special thanks to our co-author, Katie Monick. Katie completed all of the field work for this project as an undergraduate James Scholar in Animal Sciences.