The paper by Tan et al. (2013), "Into the night: camera traps reveal nocturnal activity

in a presumptive diurnal primate, Rhinopithecus brelichi" (see attached), describing nocturnal activity in R. brelichi would apparently add them to the list of primate species with cathemeral activity patterns. Could cathemerality be characteristic of species in the genus Rhinopithecus that occur at higher altitudes and, thus, are subject to greater seasonal stresses (i.e, thermal stress and reduced food availability in the winter)?