Field Estimation of Demographic Parameters: Influence of Sigmodon hispidus Population Structure

A method of removal trapping was initiated to test the hypothesis that different portions of a population of Sigmodon hispidus responded differently to live-trap sampling. Four plots of 3.7 hectares were live-trapped in 7 two-night trapping periods during one year. Animals captured the first night were temporarily removed until after the second night captures were recorded. Mean body weights and numbers were treated separately for males and females. During certain parts of the year, there were significant differences in body weight and distribution of size class between first and second night samples, but no significant differences in sex ratio. Such differences, unless accounted for by modification of sampling methods, violate assumptions of density estimators and hence markedly influence calculations of demographic parameters.