Soil-eating behavior in Formosan macaques (Macaca cyclopis) at Shoushan Nature Park of southern Taiwan

Abstract

In this first study of soil-eating behavior in Formosan macaques, we attempted to test the mineral supplementation hypothesis, and to document macaques using excavation sites at both the individual and social group levels. We observed macaques’ soil-eating behavior from October 1999 to January 2000 at Shoushan Nature Park in southern Taiwan, and compared the chemical compositions of soils from their excavation sites with those of randomly selected topsoils that were not eaten by macaques in the study area. Our results show that soils from excavation sites contained significantly higher levels of calcium than did topsoils taken from randomly selected sites. This provides evidence to support the mineral supplementation hypothesis. However, alternative hypotheses such as the treatment of diarrhea/endoparasites, detoxification, and behavioral tradition could not be excluded from explaining the occurrence of soil-eating behavior in Formosan macaques. At both the individual and social group levels, a behavioral tradition may play a particularly important role in affecting the choices of excavation sites where soil is eaten. Further research on the exact cues of excavation sites which stimulate soil-eating behavior is needed to clarify this suggestion.