Wallis, J., King, B. J. 1986. The effect of female proximity and social interaction on the menstrual cycle of crab-eating monkeys (Macaca fascicularis). Primates 27(1), 83-94.

We designed a two-cage structure that housed each member of an experimental pair in a separate cage approximately 5.5 cm apart. Thus, each animal could either maintain a safe distance from the other or reach through the cage side to give and/or receive physical contact. All control animals remained singly caged. These results suggest that close physical contact and social interaction between female crab-eating monkeys affects the reproductive cycle: females with a history of irregular and/or unusually long cycles began exhibiting more normal cycling patterns when placed in proximity to a regularly cycling female. Irregular controls continued to show cycles that were abnormally long.