J. A. Jamielniak A.G. Garcia Methodist University of Piracicaba, Piracicaba, Brazil University of Sao Paulo, Piracicaba, Brazil Computational Ecology and Software ISSN 2220-721X http://www.iaees.org/publications/journals/ces/online-version.asp 2016 6 3 83 94 International Academy of Ecology and Environmental Sciences Hong Kong 1 June 2016 18 June 2016 1 September 2016 biomathematics behavioral ecology fuzzy sets captive primates Exhibition of stress-related behaviors can be used as a criterion to evaluate the welfare of captive animals. Monitoring animal welfare is important because of ethical and conservation issues. Ethical issues are involved in maintaining animals in an environment similar to nature and conservation issues are related to scientific research and environmental education in zoos. One of the most common captive primates found in Brazilian zoos is the golden-bellied capuchin (Sapajus xanthosternos), recognized by its characteristic head coloration with a black or dark brown cap with dark sideburns and golden chest, belly and upper arms. In this paper, we developed a mathematical model that incorporated Fuzzy Theory to study stress-related behaviors in captive golden-bellied capuchin. We defined ''number of visitors'', ''number of sudden loud sounds inside the zoo'' and ''feeding period'' as input variables and the number of stress-related behaviors observed during a pre-defined time as output variable. We chose Fuzzy Theory because behavioral studies involve imprecision and a fuzzy approach provides the development of algorithms that are able to represent uncertainty inherent in data and can be an advantage in cases where an explicit analytical-process model is not available. We tested the mathematical model by comparing model results to field observations in three zoos from Brazil. This paper has revealed that the fuzzy process is a tool to help studies based on behavioral ecology since the model successfully predicted the number of stress-related behaviors presented by the animals. DOI 10.0000/issn-2220-721x-compuecol-2016-v6-0008 http://www.iaees.org/publications/journals/ces/articles/2016-6(3)/mathematical-approach-stress-related-behaviors-in-golden-bellied-capuchins.pdf