Ecological studies of coypus Myocastor coypus in their native range

GUICHÓN ML

Pavia

Jornada; Convegno Internazionale “Los straniero dei corsi d’aqua: il caso nutria (Myocastor coypus), esperienze di gestione a confronto”,; 2011

The coypu or nutria Myocastor coypus is a semiaquatic rodent found in a variety of aquatic habitats including different types of wetlands, ponds, lakes, and also lineal habitats like rivers and streams of Argentina. Habitat use at small spatial scales differs according to habitat characteristics, food availability, predation risk and hunting pressure. In lineal habitats, coypus build burrow systems on the bank and forage in the water or close to it (<10 m from water) when vegetation is available. In marshlands, coypus build nests in tall sedges and grasses growing in shallow water and forage mainly in the interface between areas with tall and short vegetation. Coypus feed mainly on aquatic and hygrophilic plants, and, to a lesser extent, on terrestrial plants available near the water’s edge. When food availability near the water becomes scarce, coypus are forced to forage further into land. Selection of foraging areas in or close to the water as a way of reducing predation risk and aid in thermo-regulation explains diet composition better than food preferences based on its quality. This behaviour has important consequences when evaluating potential impact on crops, as coypus would only damage crops cultivated next to the water or if natural vegetation is scarce. Coypus have a polygynous mating system and live in social groups that are typically composed by about 11 individuals including several adult and subadult males and females, one dominant male, and a variable number of juveniles. Spatial segregation among groups may depend on habitat characteristics, being more evident in a lineal habitat than in a pond. Behavioural observations were supported by genetic studies resulting in large genetic variability among groups of coypus in linear habitats though genetic differences were not important among groups living in a pond, where one dominant male could monopolize most paternities. Different behaviour according to habitat characteristics suggest that in linear habitats social behaviour determines coypu distribution along watercourses (parallel to water edge) while foraging behaviour determines habitat use in relation to distance to water (perpendicular to water edge). In the Pampas coypus inhabit a relatively stable environment across seasons, in contrast to the severe winters in Europe where individuals put on weight more quickly, reach sexual maturity at a younger age and frequently live at higher population densities than in this region. Densities of 6-8 ind/ha were reported in native range for non-hunted sites, though differences in food abundance, predation, climatic conditions and hunting pressure may result in large variability in coypu abundance. Along rivers and streams of the rural-urban matrix of the Pampas, coypus heterogeneous distribution at a large spatial scale was better explained by a negative association with urban areas and human density than by resource availability or the width of the alluvial plain. Coypus living close to human settlements are expected to suffer strong hunting pressure, which can also be assessed by accessibility of hunting sites, effective control of hunting and human population density of the area. Coypus are tolerant to human presence and they can form stable populations, even in urban and recreational areas, when they are not hunted. Therefore, hunting pressure would be the main determinant of coypu distribution at macro-habitat and landscape scales in the Pampas. Harvest or control plans would benefit by explicitly incorporating the spatial array of hunting areas in relation to large scale distribution of coypus and environmental features.