Home Range and Movement of Nutria (Myocastor coypus) along a Selected Stretch of the Rio Grande River, Big Bend National Park, Texas

Abstract

I investigated the home range and movement patterns of nutria (Myocastor coypus) along a section of the Rio Grande River in Big Bend National Park (BBNP). Nutria, an exotic semi-aquatic South American rodent, currently are found mainly in the south-central, southeastern and Atlantic coastal areas of the United States where they are known to damage wetland ecosystems. This introduced species continues to expand its range in the United States. Nutria first appeared in BBNP in the mid 1990s. Since that time, they have continued to move upriver and into adjacent wetland habitats. The study site was centered at the beaver pond near the Rio Grande Village campground and includes the areas between the pond and the river as well as a ~4.5 km corridor along the river from Daniel’s Ranch to the Boquillas Crossing area. The beaver pond and surrounding spring ponds are home to populations of the federally endangered Big Bend Mosquitofish (Gambusia gaigei). Seven adult nutria were captured, sedated, measured, marked, collared, and released during seven data collecting trips during the summers from May 2004 to June 2005. Collared nutria were tracked by radio telemetry techniques, and GPS coordinates were taken of their locations. An average of 27 locations per animal was used to calculate minimum convex polygon (MCP) home ranges and daily movement distances for five nutria (3 male and 2 female) using ArcMap software. The average home-range sizes were 10.05 ha (14.81 ha for males, 2.91 for females), and the mean maximum daily distance moved was 637.4 m (738.3 m for males, 486 m for females). Poor trap success and low sample size resulted in limited data. Data resulted in larger home ranges for males than females. This was comparable to other studies. Home range sizes for males were larger than other documented estimates. Mean daily movement distances of nutria in BBNP were similar to nutria in other locations.