Assessment of capybara (Hydrochoerus hydrochaeris) populations in the wetlands of Corrientes, Argentina

Abstract

Ten sampling sites were selected to represent six distinct habitat types used by capybaras (‘clean’ lagoons, ‘dirty’ lagoons, cutwaters, fens and marshes, gallery forests, and erosion ditches). The sites were sampled during winter (July and August); densities were expressed as number of capybaras per linear km of shoreline (C/LKS). The sites were classified as protected from poachers (P), under light hunting pressure (LHP), and under heavy hunting pressure (HHP). ‘Clean’ protected (P) lagoons had three times as many capybaras as LHP ones (30.7 and 10.9 C/LKS, respectively), and thirty times those under HHP (1.0 C/LKS). Protected marshes and ‘dirty’ lagoons had even higher capybara densities (52.5 and 50.0 C/LKS, respectively). Gallery forests under LHP had low densities (6.3 C/LKS), and protected cutwaters intermediate densities (27.5 C/LKS). Erosion ditches had exceptionally high densities (900 C/LKS), probably because cattle were fenced out, reducing forage competition. These densities, when converted to the standard unit area measurement (individuals/ha), were similar to those obtained by other researchers in the Brazilian Pantanal, and somewhat smaller than those in the Venezuelan Llanos. Mean number of capybaras per group remained relatively constant in all habitats (averages ranged between 9.2 and 11.8 individuals/group) but its coefficient of variation was much higher in LHP sites, probably because social structure was altered severely by hunting. The overall ratio of young to adults and juveniles was 1:7.4. In one of the sites, 13 of 34 groups (38.2%) were with young (average of 17 capybaras per group, 4.7 of which were young), confirming that this species can reproduce all year long.