A capybara (Hydrochaeris hydrochaeris) population was monitored weekly at nightfall for 12 months (February 2003 to January 2004). Information about behavior, age class and animal number at pasture activities were collected during the observations. Fifteen animals were captured once and thus, their contention, weighing, identifications, sex definition, as well as, the age class confirmation could be done. The average ecological density was 0,58±0,05ind ha-1 and the mean individual number was 21±5,6. The capybara group changed its behavior by increasing the pasture area and decreasing the number of animals observed (mainly juveniles) from June to September (2003). Juvenile males were probably banished from the group to provide population adjust because of reproduction season and food scarcity. Home-range increase during dry season added to animals' banishment for food and/or reproduction reasons show the capybaras' ability to react against difficult environmental conditions during the year.
behavior; Hydrochaeris hydrochaeris; ecological density; home-range
