Behavioral Interactions in Sigmodon fulviventer and S. hispidus

A laboratory study of intra- and interspecific behavioral interactions between the cotton rats, Sigmodon fulviventer and S. hispidus from Durango, México, suggests that S. fulviventer is behaviorally dominant over S. hispidus. When interspecific agonistic behavior occurred, S. fulviventer was generally the more aggressive of the two. In contrast, S. hispidus more often avoided encounters. Over half the interspecific encounters resulted in neutral or amicable relationships, suggesting that avoidance or peaceful coexistence is more important than aggression during interactions in the field. Intraspecific interactions in both species were generally positive (non-aggressive, no avoidance or amicable). Results of the tests were in agreement with measurements of interspecific association using field data. These behavioral mechanisms may play important roles in natural spatial segregation and ultimately in population regulation of S. hispidus.