Disappearance rate of chimpanzee scats: Implications for census work on Pan troglodytes

Scat (faeces) decay rate estimates are used to calculate animal species abundance and density. For African great apes, this has been measured only for Gorilla; chimpanzee scats are assumed to decay at a faster rate due to lower fibre content. We provide the first systematic measure of scat decay rate duration for Pan troglodytes schweinfurthii, in Kanyawara, Kibale National Park, Uganda. We used two methods: (1) multiple visits to obtain prospective decay rates (PDR) (N = 96 scats) and (2) a novel approach of time-lapse photography (TLP) (N = 17 scats). Most of the visited scats (67%) decayed in ≤24 hr, and median decay rate duration from photographic documentation was 18 hr. Using regression analyses, we tested 11 covariables to determine predictors for decay rate duration. Greater volume of scat and reduced levels of diurnal dung beetle activity were positively associated with longer decay rate duration. Given a high prevalence of dung beetle activity (88% of scats), particularly within 3 hr post-defaecation, we suggest the use of the alternative term, disappearance rate of scats. With a rapid disappearance rate, scat count surveys of unhabituated chimpanzees are challenging; further work is then needed for Pan spp. to determine spatial and temporal differences at intra- and inter-species level.